Evolution of the vertebrate brain. The brain of vertebrates and its evolution The development of parts of the vertebrate brain is associated with

The formation of the brain in all vertebrates begins with the formation of three swellings or brain vesicles at the anterior end of the neural tube: anterior, middle and posterior. Subsequently, the anterior medullary vesicle is divided by a transverse constriction into two sections. The first of them (anterior) forms the anterior part of the brain, which in most vertebrates forms the so-called cerebral hemispheres. The diencephalon develops at the back of the forebrain. The midbrain does not divide and is completely transformed into the midbrain. The posterior brain vesicle is also divided into two sections: in its anterior part the hindbrain or cerebellum is formed, and from the posterior section the medulla oblongata is formed, which passes into the spinal cord without a sharp boundary.

During the formation of the five cerebral vesicles, the cavity of the neural tube forms a series of extensions, which are called cerebral ventricles. The cavity of the forebrain is called the lateral ventricles, the intermediate - the third ventricle, the medulla oblongata - the fourth ventricle, the midbrain - the Sylvian canal, which connects the 3rd and 4th ventricles. The hindbrain does not have a cavity. In each part of the brain there is a roof, or mantle, and a bottom, or base. The roof is made up of the parts of the brain that lie above the ventricles, and the bottom is made up of the parts below the ventricles.

The substance of the brain is heterogeneous. Dark areas are gray matter, light areas are white matter. White matter is a collection of nerve cells with a myelin sheath (many lipids that give a whitish color). Gray matter is a collection of nerve cells between neuroglial elements. The layer of gray matter on the surface of the roof of any part of the brain is called the cortex. Thus, in all vertebrates the brain consists of five sections located in the same sequence. However, the degree of their development is not the same among representatives of different classes. These differences are due to phylogeny. There are three types of brain: ichthyopsid, sauropsid and mammalian.

Ichthyopsid type

The ichthypsid type of brain includes the brain of fish and amphibians. The fish brain has a primitive structure, which is reflected in the small size of the brain as a whole and the weak development of the anterior section. The forebrain is small and not divided into hemispheres. The roof of the forebrain is thin. In bony fishes it does not contain nervous tissue. Its bulk is formed by the bottom, where nerve cells form two clusters - the striatum. Two olfactory lobes extend forward from the forebrain. Essentially, the forebrain of fish is only an olfactory center. The diencephalon of fish is covered from above by the forebrain and middle brain. A growth extends from its roof - the pineal gland; from the bottom - a funnel with the adjacent pituitary gland and optic nerves.

The midbrain is the most developed part of the fish brain. This is the visual center of fish and consists of two optic lobes. On the surface of the roof is a layer of gray matter (bark). This is the highest part of the fish brain, since signals from all stimuli come here and response impulses are produced here. The cerebellum of fish is well developed, since the movements of fish are varied. The medulla oblongata in fish has highly developed visceral lobes and is associated with the strong development of taste organs.

The amphibian brain has a number of progressive changes, which are associated with the transition to life on land, which are expressed in an increase in the total volume of the brain and the development of its anterior section. At the same time, the forebrain is divided into two hemispheres. The roof of the forebrain consists of nervous tissue. At the base of the forebrain lie the striatum. The olfactory lobes are sharply limited from the hemispheres. The forebrain still has the significance of only the olfactory center.

The diencephalon is clearly visible from above. Its roof is formed by an appendage - the pineal gland, and the bottom - the pituitary gland. The midbrain is smaller in size than that of fish. The midbrain hemispheres are well defined and covered with cortex. This is the leading department of the central nervous system, because This is where the received information is analyzed and response impulses are generated. It retains the importance of the visual center. The cerebellum is poorly developed and has the appearance of a small transverse ridge at the anterior edge of the rhomboid fossa of the medulla oblongata. Poor development of the cerebellum corresponds to simple movements of amphibians.

Sauropsid type

The sauropsid brain type includes the brains of reptiles and birds. In reptiles, there is a further increase in brain volume. The forebrain becomes the largest section due to the development of the striatum, i.e. grounds. The roof (mantle) remains thin. For the first time in the process of evolution, nerve cells or a cortex appear on the surface of the roof, which has a primitive structure (three layers) and is called the ancient cortex - archeocortex. The forebrain ceases to be only an olfactory center. It becomes the leading department of the central nervous system.

The diencephalon is interesting due to the structure of the dorsal appendage (parietal organ or parietal eye), which reaches its highest development in lizards, acquiring the structure and function of the organ of vision. The midbrain decreases in size, loses its importance as a leading section, and its role as a visual center decreases. The cerebellum is relatively better developed than in amphibians.

The bird brain is characterized by a further increase in its total volume and the enormous size of the forebrain, which covers all other parts except the cerebellum. The increase in the forebrain, which, like in reptiles, is the leading part of the brain, occurs at the expense of the bottom, where the striatum develops strongly. The roof of the forebrain is poorly developed and has a small thickness. The cortex does not receive further development, and even undergoes reverse development - the lateral section of the cortex disappears.

The diencephalon is small, the pineal gland is poorly developed, the pituitary gland is well expressed. The optic lobes are developed in the midbrain, because vision plays a leading role in the life of birds. The cerebellum reaches enormous sizes and has a complex structure. It has a middle part and side protrusions. The development of the cerebellum is associated with flight.

Mammal type

The mammalian brain type includes the brain of mammals, in which the evolution of the brain went in the direction of the development of the forebrain roof and hemispheres. The increase in the size of the forebrain occurs due to the roof, and not the bottom, as in birds. A layer of gray matter appears on the entire surface of the roof - bark. The mammalian cortex is not homologous to the ancient reptile cortex, which serves as an olfactory center. This is a completely new structure that arises during the evolution of the nervous system. In lower mammals the surface of the cortex is smooth, in higher mammals it forms numerous convolutions that sharply increase its surface. The cortex takes on the role of the leading part of the brain, which is characteristic of the mammary type of brain. The olfactory lobes are highly developed, because in many mammals they are a sensory organ.

The diencephalon has characteristic appendages - the pineal gland and the pituitary gland. The midbrain is reduced in size. Its roof, in addition to the longitudinal furrow, also has a transverse one. Therefore, instead of two hemispheres (optic lobes), four tubercles are formed. The anterior ones are associated with visual receptors, and the posterior ones are associated with auditory receptors. The cerebellum develops progressively, which is expressed in a sharp increase in the size of the organ and its complex external and internal structure. In the medulla oblongata, on the sides there is a path of nerve fibers leading to the cerebellum, and on the lower surface there are longitudinal ridges (pyramids).

Evolution of the brain in vertebrates: main stages

Stage 1. The formation of the central nervous system in the form of a neural tube first appears in animals of the chordate type. In lower chordates, for example, the lancelet, the neural tube is preserved throughout life; in higher chordates - vertebrates - in the embryonic stage, a neural plate is laid on the dorsal side of the embryo, which sinks under the skin and folds into a tube.

Stage 2. In vertebrates, the neural tube is divided into the brain and spinal cord. In the embryonic stage of development, the neural tube forms three swellings in the anterior part - three brain vesicles, from which parts of the brain develop: the anterior vesicle gives rise to the forebrain and diencephalon, the middle vesicle turns into the midbrain, the posterior vesicle forms the cerebellum and medulla oblongata. These five brain regions are characteristic of all vertebrates.

Stage 3. Lower vertebrates - fish and amphibians - are characterized by a predominance of the midbrain over other parts. Only in cartilaginous shark fishes, due to rapid movement, the cerebellum is developed, and a highly developed sense of smell led to an increase in the forebrain, which becomes the center for processing olfactory signals.

Stage 4. In amphibians, the forebrain increases slightly and a thin layer of nerve cells is formed in the roof of the hemispheres - the primary medullary vault (archipallium), the ancient cortex. In addition to the archipallium, connections between the forebrain and midbrain are strengthened in amphibians.

Stage 5. In reptiles, the forebrain increases significantly due to accumulations of nerve cells - striatum - at the bottom of the forebrain. Most of the roof of the hemispheres is occupied by the ancient cortex. For the first time in reptiles, the rudiment of a new cortex appears - neopallium. The hemispheres of the forebrain creep onto other parts, as a result of which a bend is formed in the region of the diencephalon. Beginning with ancient reptiles, the cerebral hemispheres became the largest part of the brain.

The brain structure of birds and reptiles has much in common. On the roof of the brain is the primary cortex, the midbrain is well developed. However, in birds, compared to reptiles, the total brain mass and the relative size of the forebrain increase. Large optic lobes of the midbrain indicate an increased role of vision in bird behavior. The cerebellum is large and has a folded structure. A significant part of the forebrain hemispheres in birds, as in reptiles, is formed by the striatum - growths of the bottom of the forebrain.

Stage 6. In mammals, the forebrain reaches its greatest size and complexity. Most of the brain matter is made up of the new cortex - the secondary medullary vault, or neopallium. It consists of nerve cells and fibers arranged in several layers. The neocortex of the cerebral hemispheres serves as the center of higher nervous activity.

The intermediate and middle parts of the brain in mammals are small. The expanding hemispheres of the forebrain cover them and crush them under themselves. In primates, the forebrain hemispheres also cover the cerebellum, and in humans, the medulla oblongata. Some mammals have a smooth brain without grooves or convolutions, but most mammals have grooves and convolutions in the cerebral cortex that form as the cortex grows. The largest groove formations are in cetaceans, the smallest in insectivores and bats.

Stage 7. The appearance of grooves and convolutions occurs due to the growth of the brain with limited dimensions of the skull. The brain seems to be imprinted into the bone walls of the skull, and the membranes of the brain are squeezed. Further growth of the cortex leads to the appearance of folding in the form of grooves and convolutions. In the cerebral cortex of all mammals there are nuclear zones of analyzers, i.e. fields of primary cortical analysis.

Subsequently, the anterior medullary vesicle is divided by a transverse constriction into two sections. The first of them (anterior) forms the anterior part of the brain, which in most vertebrates forms the so-called cerebral hemispheres. The diencephalon develops at the back of the forebrain. The midbrain does not divide and is completely transformed into the midbrain. The posterior brain vesicle is also divided into two sections: in its anterior part the hindbrain or cerebellum is formed, and from the posterior section the medulla oblongata is formed, which passes into the spinal cord without a sharp boundary.

Divisions of the brain of vertebrates

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Brain development. If the spinal cord in all vertebrates is developed more or less equally, then the brain differs significantly in size and complexity of structure in different animals. The forebrain undergoes particularly dramatic changes during evolution. In lower vertebrates, the forebrain is poorly developed. In fish, it is represented by the olfactory lobes and nuclei of gray matter in the thickness of the brain. The intensive development of the forebrain is associated with the exit of animals to land. It differentiates into the diencephalon and two symmetrical hemispheres, which are also called telencephalon. Gray matter on the surface of the forebrain (bark) first appears in reptiles, developing further in birds and especially in mammals. The forebrain hemispheres become truly large only in birds and mammals. In the latter, they cover almost all other parts of the brain.

Structure of the brain. The brain is divided into the following sections: medulla oblongata, hindbrain, midbrain, diencephalon and telencephalon (Fig. 48). The medulla oblongata is a direct continuation of the spinal cord and, expanding, passes into the hindbrain. On its dorsal surface there is a diamond-shaped depression - the IV ventricle. In the thickness of the medulla oblongata there are accumulations of gray matter - nuclei cranial nerves(see below). The hindbrain includes cerebellum And pons. The cerebellum is located above the medulla oblongata and has a very complex structure. On the surface of the cerebellar hemispheres, gray matter forms the cortex, and inside the cerebellum - its nuclei. The midbrain consists of cerebral peduncle And quadrigeminal. The diencephalon has two main sections - thalamus And hypothalamus, each of which consists of a large number of cores. The laterally flattened third ventricle passes through the diencephalon, which connects with the two lateral ventricles of the cerebral hemispheres.

In humans, the cerebral hemispheres form the bulk of the brain and are covered over their entire surface bark Each hemisphere is divided by grooves into lobes: frontal, parietal, occipital and temporal. The white matter of the cerebral hemispheres is formed by long processes of a huge number of neurons, the bodies of which are located in the cerebral cortex. These fibers connect the brain with the spinal cord, as well as the cortex of different lobes of the hemispheres with each other. The white matter of the cerebral hemispheres contains several accumulations of gray matter. These are the subcortical nuclei that form striped bodies.

The medulla oblongata, pons, and midbrain together form the brainstem, which contains bundles of nerve fibers connecting the forebrain with the spinal cord.

Functions of parts of the brain. There is a clear division of functions between different parts of the brain. As we move to higher and younger parts of the brain, functions become more complex.

The medulla oblongata performs relatively simple but vital functions. It contains the respiratory, cardiovascular and digestive centers, as well as centers for reflexes such as swallowing, coughing, and sucking. If the medulla oblongata is damaged, breathing stops, blood pressure drops and death occurs. In the medulla oblongata there is network formation, whose neurons send impulses to the spinal cord and maintain it in an active state. The cessation of the flow of these impulses to the spinal cord, for example, after a transection at the border between the medulla oblongata and the spinal cord or below, leads to the development of shock.

Cerebellum. The function of the cerebellum is to regulate body movements. After the destruction of the cerebellum in animals, movements do not disappear, but become poorly coordinated, inaccurate, rough, and balance is disturbed. People with impaired cerebellar function lose the ability to make precise movements (threading a needle, playing musical instruments). Over time, manifestations of cerebellar damage may disappear due to the ability of other parts of the brain to take over the functions of the destroyed parts (compensation phenomenon).

Midbrain. In lower vertebrates, the quadrigeminal midbrain is well developed and is the most important and phylogenetically young part of the brain. In mammals, its functions are transferred to the cerebral hemispheres, and the regulation of eye and ear movements remains behind the quadrigeminalis. Located in the midbrain red core, which in mammals and humans plays a major role in the regulation of skeletal muscle tone. It acts through the medulla oblongata in such a way that it enhances or weakens the activating influence of the network formation on the neurons of the spinal cord. The midbrain has a stronger effect on the tone of those muscles that counteract the force of gravity (leg extensors, back muscles).

Diencephalon. It has already been noted that the hypothalamus contains centers for regulating metabolism and body temperature. It plays a large role in coordinating (harmonizing) the activities of different systems of internal organs, in the change of sleep and wakefulness, and in the manifestation of emotions. The diencephalon, together with the midbrain, carries out complex reflex or instinctive reactions (food, defensive, etc.). Some centers of the thalamus take part in maintaining the state of attention, not allowing currently unnecessary centripetal signals to pass into the cerebral cortex. The thalamus is the pain center.

Hemispheres of the brain. The functions of this part of the central nervous system are studied based on the consequences of complete or partial removal of the forebrain in experimental animals. In lower vertebrates (fish, amphibians), removal of the forebrain is not accompanied by noticeable changes in the behavior of the animal; only the olfactory function is impaired. However, in birds and mammals, the consequences of removing the cerebral hemispheres are much more serious. A pigeon with its hemispheres removed is not able to feed itself, hardly moves and reacts weakly to irritations. Throwed up, it flies for some time, and then sits down and freezes again for a long time. In dogs, the consequences of removal of the cerebral hemispheres are even deeper. The animal reacts only to very strong irritations, does not recognize previously familiar objects, sleeps most of the time and wakes up only from a feeling of hunger or thirst, but cannot eat or drink on its own. An animal without cerebral hemispheres loses all the individual adaptations it has acquired to the conditions of existence (conditioned reflexes).

Consequently, the function of the cerebral hemispheres of the forebrain is that they ensure the complex behavior of the animal, its subtle adaptation to continuously changing conditions of existence. Located in the depths of the hemispheres, the striatum, together with the diencephalon and midbrain, regulate the instinctive behavior and motor activity of animals and humans.

The surface of the cerebral hemispheres in higher vertebrates is covered with a layer of gray matter - the cortex. The cerebral cortex plays such an important role in the life of mammals and especially humans that its structure and functions should be considered separately.

Cerebral cortex. The surface of the human cerebral cortex is about 1500 cm 2, which is many times greater than the inner surface of the skull. Such a large surface of the cortex was formed due to the development of a large number of grooves and convolutions, as a result of which most of the cortex (about 70%) is concentrated in the grooves. The largest grooves of the cerebral hemispheres are the central one, which runs across both hemispheres, and the temporal one, which separates the temporal lobe of the brain from the rest.

The cerebral cortex, despite its small thickness (1.5-3 mm), has a very complex structure. It has six main layers, which differ in the structure, shape and size of neurons and connections. The microscopic structure of the cortex was studied for the first time at the end of the last century by V. A. Betz. He discovered pyramidal neurons, which were later given his name (Betz cells). In total, according to the latest data, there are up to 50 billion neurons in the cerebral cortex, and they are arranged there in columns or columns.

Based on experiments with partial removal of different sections of the cortex in animals and observations of people with damaged cortex, it was possible to establish the functions of different parts of the cortex. Thus, in the cortex of the occipital lobe of the hemispheres there is the visual center of the upper part of the temporal lobe - the auditory one. The musculocutaneous zone, which perceives irritations from the skin of all parts of the body and controls voluntary movements of skeletal muscles, occupies a section of the cortex on both sides of the central sulcus. Each part of the body has its own section of the cortex, and the representation of the palms and fingers, lips and tongue, as the most mobile and sensitive parts of the body, occupies almost the same area of the cortex in humans as the representation of all other parts of the body combined.

The cortex contains the centers of all sensory (receptor) systems, representatives of all organs and parts of the body. In this regard, centripetal nerve impulses from all internal organs or parts of the body approach the cortex, and it can control their work. Through the cerebral cortex, conditioned reflexes are closed, through which the body constantly, throughout life, very precisely adapts to the changing conditions of existence, to the environment.

Biology lesson on the topic: "Regulation of vital processes of vertebrate animals"

Lesson equipment:

Program and textbook by N.I. Sonin “Biology. Living organism". 6th grade.
Handout – grid table “Divisions of the brain of vertebrates”.
Vertebrate brain models.
Inscriptions (names of animal classes).
Drawings depicting representatives of these classes.

During the classes.

I. Organizational moment.

II. Homework repetition (frontal survey):

What systems provide regulation of the activity of the animal’s body?
What is irritability or sensitivity?
What is a reflex?
What are the types of reflexes?
What are these reflexes?

a) does a person produce saliva in response to the smell of food?

b) does the person turn on the light despite the absence of a light bulb?

c) does the cat run to the sound of the refrigerator door opening?

d) does the dog yawn?

What kind of nervous system does hydra have?

How does the nervous system of an earthworm work?

III. New material:

(? – questions asked to the class during the explanation)

We are studying section 17 now, what is it called?

Coordination and regulation of what?

What animals have we already talked about in class?

Are they invertebrates or vertebrates?

What groups of animals do you see on the board?

Today in the lesson we will study the regulation of the vital processes of vertebrate animals.

Topic: “Regulation in vertebrates” (write in notebooks).

Our goal will be to consider the structure of the nervous system of various vertebrates. At the end of the lesson we will be able to answer the following questions:

How is animal behavior related to the structure of the nervous system?
Why is it easier to train a dog than a bird or a lizard?
Why can pigeons turn over while flying?

During the lesson we will fill out the table, so everyone has a piece of paper with the table on their desk.

In vertebrates, the nervous system is located on the dorsal side of the body. It consists of the brain, spinal cord and nerves.

1) where is the spinal cord located?

2) where is the brain located?

It distinguishes between the forebrain, midbrain, hindbrain and some other sections. In different animals these sections are developed differently. This is due to their lifestyle and the level of their organization.

Now we will listen to reports on the structure of the nervous system of different classes of vertebrates. And you make notes in the table: is this part of the brain present or not in this group of animals, how is it developed in comparison with other animals? Once completed, the table remains with you.

(The table must be printed in advance according to the number of students in the class)

Before the lesson, inscriptions and drawings are attached to the board. While answering, students hold models of the vertebrate brain in their hands and show the parts they are talking about. After each answer, the model is placed on the demonstration table near the board under the inscription and drawing of the corresponding group of animals. It turns out something like this...

A – inscriptions (names of animal classes)

B – drawings depicting representatives of these classes

C – vertebrate brain models).

1. Pisces.

Spinal cord. The central nervous system of fish, like that of the lancelet, has the shape of a tube. Its posterior section, the spinal cord, is located in the spinal canal formed by the upper bodies and arches of the vertebrae. From the spinal cord between each pair of vertebrae, nerves extend to the right and left that control the functioning of the muscles of the body and fins and organs located in the body cavity.

Signals of irritation are sent via nerves from sensory cells on the fish’s body to the spinal cord.

Brain. The anterior part of the neural tube of fish and other vertebrates is modified into the brain, protected by the bones of the skull. The vertebrate brain is divided into sections: forebrain, diencephalon, midbrain, cerebellum and medulla oblongata. . All these parts of the brain are of great importance in the life of fish. For example, the cerebellum controls the coordination of movement and balance of the animal. The medulla oblongata gradually passes into the spinal cord. It plays a large role in controlling breathing, blood circulation, digestion and other essential functions of the body.

Let's see what you wrote down?

2.Amphibians and reptiles.

The central nervous system and sensory organs of amphibians consist of the same sections as those of fish. The forebrain is more developed than in fish, and two swellings can be distinguished in it - large hemispheres. Amphibians' bodies are close to the ground and they do not have to maintain balance. In connection with this, the cerebellum, which controls the coordination of movements, is less developed in them than in fish. The nervous system of a lizard is similar in structure to the corresponding systems of amphibians. In the brain, the cerebellum, which controls balance and coordination of movements, is more developed than in amphibians, which is associated with the greater mobility of the lizard and the significant variety of its movements.

3.Birds.

Nervous system. The visual thalamus of the midbrain is well developed in the brain. The cerebellum is much larger than in other vertebrates, since it is the center of coordination and coordination of movements, and birds make very complex movements in flight.

Compared to fish, amphibians and reptiles, birds have enlarged forebrain hemispheres.

4. Mammals.

The mammalian brain consists of the same parts as those of other vertebrates. However, the cerebral hemispheres of the forebrain have a more complex structure. The outer layer of the cerebral hemispheres consists of nerve cells that form the cerebral cortex. In many mammals, including dogs, the cerebral cortex is so enlarged that it does not lie in an even layer, but forms folds - convolutions. The more nerve cells in the cerebral cortex, the more developed it is, the more convolutions it has. If the cerebral cortex of an experimental dog is removed, then the animal retains its innate instincts, but conditioned reflexes are never formed.

The cerebellum is well developed and, like the cerebral hemispheres, has many convolutions. The development of the cerebellum is associated with the coordination of complex movements in mammals.

What parts of the brain do all classes of animals have?
Which animals will have the most developed cerebellum?
Forebrain?
Which ones have a cortex on their hemispheres?
Why is the frog's cerebellum less developed than that of fish?

Now let's look at the structure of the sense organs of these animals, their behavior, in connection with this structure of the nervous system ( told by the same students who talked about the structure of the brain ):

1. Pisces.

Sense organs allow fish to navigate their environment well. The eyes play an important role in this. Perch sees only at a relatively close distance, but distinguishes the shape and color of objects.

In front of each eye of the perch there are two nostril openings, leading into a blind sac with sensitive cells. This is the organ of smell.

The hearing organs are not visible from the outside; they are located on the right and left of the skull, in the bones of the back part. Due to the density of water, sound waves are well transmitted through the bones of the skull and are perceived by the hearing organs of the fish. Experiments have shown that fish can hear the footsteps of a person walking along the shore, the ringing of a bell, or a gunshot.

The taste organs are sensitive cells. They are located in perch, like other fish, not only in the oral cavity, but also scattered over the entire surface of the body. There are also tactile cells there. Some fish (for example, catfish, carp, cod) have tactile antennae on their heads.

Fish are characterized by a special sensory organ - the lateral line. . A series of holes are visible on the outside of the body. These holes are connected to a channel located in the skin. The canal contains sensory cells connected to a nerve running under the skin.

The lateral line perceives the direction and strength of water flow. Thanks to the lateral line, even blinded fish do not bump into obstacles and are able to catch moving prey.

Why can't you talk loudly while fishing?

2.Amphibians.

The structure of the sense organs corresponds to the terrestrial environment. For example, by blinking its eyelids, a frog removes dust particles adhering to the eye and moistens the surface of the eye. Like fish, the frog has an inner ear. However, sound waves travel much worse in air than in water. Therefore, for better hearing, the frog also has a middle ear. . It begins with the sound-receiving eardrum, a thin round membrane behind the eye. From it, sound vibrations are transmitted through the auditory bone to the inner ear.

When hunting, vision plays a major role. Having noticed any insect or other small animal, the frog throws out a wide sticky tongue from its mouth, to which the victim sticks. Frogs only grab moving prey.

The hind legs are much longer and stronger than the front legs; they play a major role in movement. A sitting frog rests on slightly bent forelimbs, while the hind limbs are folded and located on the sides of the body. Quickly straightening them, the frog makes a jump. The front legs protect the animal from hitting the ground. The frog swims, pulling and straightening its hind limbs, while pressing its front limbs to its body.

How do frogs move in water and on land?

3.Birds.

Sense organs. Vision is best developed - when moving quickly in the air, only with the help of the eyes can one assess the situation from a long distance. The sensitivity of the eyes is very high. In some birds it is 100 times greater than in humans. In addition, birds can clearly see objects that are in the distance and distinguish details that are just a few centimeters from the eye. Birds have color vision that is better developed than other animals. They distinguish not only primary colors, but also their shades and combinations.

Birds hear well, but their sense of smell is weak.

Bird behavior is very complex. True, many of their actions are innate and instinctive. These are, for example, behavioral features associated with reproduction: pair formation, nest building, incubation. However, throughout their lives, birds develop more and more conditioned reflexes. For example, young chicks are often not at all afraid of humans, but with age they begin to treat people with caution. Moreover, many learn to determine the degree of danger: they have little fear of unarmed people, but fly away from a person with a gun. Domestic and tame birds quickly get used to recognizing the person feeding them. Trained birds are capable of performing various tricks at the direction of the trainer, and some (for example, parrots, mynahs, crows) learn to quite clearly repeat various words of human speech.

4. Mammals.

Sense organs. Mammals have developed senses of smell, hearing, vision, touch and taste, but the degree of development of each of these senses varies from species to species and depends on their lifestyle and environment. Thus, a mole living in the complete darkness of underground passages has underdeveloped eyes. Dolphins and whales hardly distinguish between smells. Most land mammals have a very sensitive sense of smell. It helps predators, including dogs, to track prey; herbivores at a great distance can sense a creeping enemy; animals detect each other by smell. Hearing in most mammals is also well developed. This is facilitated by the sound-catching ears, which in many animals are mobile. Those animals that are active at night have especially sensitive hearing. Vision is less important for mammals than for birds. Not all animals distinguish colors. Only monkeys see the same range of colors as humans.

The organs of touch are special long and coarse hair (the so-called “whiskers”). Most of them are located near the nose and eyes. Bringing their heads closer to the object being examined, mammals simultaneously sniff, examine and touch it. In monkeys, like in humans, the main organs of touch are the tips of the fingers. Taste is especially developed in herbivores, who, thanks to this, easily distinguish edible plants from poisonous ones.

The behavior of mammals is no less complex than the behavior of birds. Along with complex instincts, it is largely determined by higher nervous activity, based on the formation of conditioned reflexes during life. Conditioned reflexes are developed especially easily and quickly in species with a well-developed cerebral cortex.

From the first days of life, mammalian cubs recognize their mother. As they grow, their personal experience with the environment is continuously enriched. The games of young animals (wrestling, mutual pursuit, jumping, running) serve as good training for them and contribute to the development of individual attack and defense techniques. Such games are typical only for mammals.

Due to the fact that the environmental situation is extremely changeable, mammals constantly develop new conditioned reflexes, and those that are not reinforced by conditioned stimuli are lost. This feature allows mammals to quickly and very well adapt to environmental conditions.

Which animals are the easiest to train? Why?

Biology and medicine

Evolution of the brain in vertebrates: main stages

A significant part of the forebrain hemispheres in birds, as in reptiles, is formed by the striatum - growths of the bottom of the forebrain.

Evolution of the brain in vertebrates

The formation of the brain in the embryos of all vertebrates begins with the appearance of swellings at the anterior end of the neural tube - brain vesicles. At first there are three of them, and then five. From the forebrain, the forebrain and diencephalon are subsequently formed, from the middle - the mesencephalon, and from the posterior - the cerebellum and medulla oblongata. The latter passes into the spinal cord without a sharp boundary

In the neural tube there is a cavity - the neurocoel, which, during the formation of five brain vesicles, forms extensions - the cerebral ventricles (in humans there are 4). In these areas of the brain, a bottom (base) and a roof (mantle) are distinguished. The roof is located above and the bottom is located below the ventricles.

The brain matter is heterogeneous - it is represented by gray and white matter. The gray is a collection of neurons, and the white is formed by the processes of neurons, covered with a fat-like substance (myelin sheath), which gives the brain substance its white color. The layer of gray matter on the roof of any part of the brain is called the cortex.

The sense organs play a major role in the evolution of the nervous system. It was the concentration of the sensory organs at the anterior end of the body that determined the progressive development of the head section of the neural tube. It is believed that the anterior brain vesicle was formed under the influence of the olfactory, the middle - visual, and the posterior - auditory receptors.

The forebrain is small, not divided into hemispheres, and has only one ventricle. Its roof does not contain nerve elements, but is formed by epithelium. Neurons are concentrated at the bottom of the ventricle in the striatum and in the olfactory lobes extending in front of the forebrain. Essentially, the forebrain functions as an olfactory center.

The midbrain is the highest regulatory and integrative center. It consists of two optic lobes and is the largest part of the brain. This type of brain, where the highest regulatory center is the midbrain, is called ichthyopsid. .

The diencephalon consists of a roof (thalamus) and a bottom (hypothalamus). The pituitary gland is connected to the hypothalamus, and the pineal gland is connected to the thalamus.

The cerebellum in fish is well developed, since their movements are very diverse.

The medulla oblongata, without a sharp boundary, passes into the spinal cord and the food, vasomotor and respiratory centers are concentrated in it.

10 pairs of cranial nerves depart from the brain, which is typical for lower vertebrates

Amphibians have a number of progressive changes in the brain, which is associated with the transition to a terrestrial lifestyle, where conditions, compared to the aquatic environment, are more diverse and are characterized by the variability of operating factors. This led to the progressive development of the senses and, accordingly, the progressive development of the brain.

Forebrain the amphibian is much larger in comparison with fish; it has two hemispheres and two ventricles. Nerve fibers appeared in the roof of the forebrain, forming the primary medullary vault - archipallium . The cell bodies of neurons are located in depth, surrounding the ventricles, mainly in the striatum. The olfactory lobes are still well developed.

The highest integrative center remains the midbrain (ichthyopsid type). The structure is the same as that of fish.

The cerebellum, associated with the primitiveness of amphibian movements, has the appearance of a small plate.

The diencephalon and medulla oblongata are the same as in fish. There are 10 pairs of cranial nerves leaving the brain.

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Brain

The brain (lat. Encephalon (borrowed from Greek), ancient Greek ἐγκέφαλος) is the main section of the central nervous system (neuraxis) of all vertebrates, in which it is contained in a “box” - the skull. The brain is also found in many invertebrate animals with different types of nervous systems. The process of evolutionary formation of the brain is called “cephalization”.

The brain is made up of different types of neurons that form the gray matter of the brain (cortex and nuclei). Their processes (axons and dendrites) form white matter. White and gray matter, as well as neuroglia, form nervous tissue, from which, among other things, the brain is formed. Brain neurons communicate with each other and with neurons in other parts of the nervous system thanks to universal nerve connections - synapses.

Brain structures are responsible for performing a wide variety of tasks: from controlling vital functions to higher mental activity.

Embryogenesis

Brain development in invertebrates

The development of the central nervous system and ganglia in invertebrates shares some similarities with vertebrates. First of all, their nervous system is a derivative of the ectoderm. Secondly, the CNS is formed as a result of the migration of neurons. The difference is that in vertebrates the ectoderm from which the central nervous system will arise is located dorsally. Experiments on Drosophila and Caenorhabditis elegans showed that the “nervous” ectoderm is either located ventrally (Drosophila) or migrates from the lateral side to the anterior side (C. elegans), and then plunges into the thickness of the embryo. The next stage is the formation of the “brain,” that is, the conglomeration of neurons in the anterior ganglion.

Brain development in vertebrates

Formation of anatomical structures

The vertebrate nervous system is a derivative of the neural plate, which is also a derivative of the ectoderm. Subsequently, the neural plate turns into the neural tube. In the middle of the tube a cavity of the same shape is formed - the neurocoel. It is in the cranial region of the neural tube that the brain develops. However, it should be noted that the medullary thickening is still present in the neural plate. The neural tube consists of layers: ventral, dorsal and lateral. The lateral plate along its length is divided by the interstitial groove (the groove of His) into the ventral lateral (basal) and dorsolateral (alarna (Krylov)) plates. With further development, these plates are located in the spinal cord, medulla oblongata and medial cord. Motor components are formed from the basal plate, and sensory components are formed from the alar plate.

The first stage of brain development is the appearance of the anterior fold of the brain (lat. Plica ventralis encephali). It divides the existing thickening into two “regions”: the archencephalon, which is located in front of the notochord, and the deuteroencephalon, which is located behind it. The next stage of development is the stage of three primary vesicles: the forebrain (lat. Prosencephalon), the midbrain (lat. Mesencephalon) and the rhombencephalon (lat. Rhombencephalon). The first bladder is a derivative of archencephalon, the other two are deuteroencephalon. The stage of three bubbles passes into the stage of five tertiary ones: the forebrain is divided into the telencephalon (lat. Telencephalon) and the diencephalon (lat. Diencephalon); the rhombencephalon is divided into the hindbrain (lat. metencephalon) and the medulla oblongata (lat. myelencephalon seu medulla oblongata). The midbrain does not divide. Subsequently, the hindbrain gives rise to the cerebellum and pons (the latter develops only in mammals). During development, some parts of the brain grow faster than others, which leads to the appearance (in reptiles, birds and mammals) of brain curves: the cerebral, pontine (only in mammals and cervical). The neurocoelum of the rhomboid brain turns into the fourth ventricle, the middle one into the aqueduct (lat. Aqueductus), the intermediate into the third ventricle and the terminal into the first and second ventricles.

Histogenesis and neuronal migration

The brain consists of neurons and glia and has similar histogenesis features to the spinal cord. All brain cells originate from neuroblasts; all cytoarchitecture must first have the same three-layer structure for the entire central nervous system - marginal, mantle and matrix layers.

Also in the brain, processes of neuronal migration occur, which are of two types - radial, when neurons are directed perpendicular to the ventricular surface, and tangential, when this movement is parallel. A clear example of this is the formation of the neocortex. It consists of multi-stage migration of neurons. At first, the structure of the cortex is similar to other parts of the nervous system and consists of three layers. Subsequently, a population of specific neurons, Cajal-Retzius cells, appears in the marginal layer. These neurons secrete several control factors that influence neuronal migration. The most important of them is relin. Under its influence, future cortical neurons migrate from the ventricular region to the marginal layer, where they form the cortical plate. This plate will in the future become layer VI of the neocortex. Subsequently, the layers are formed in order from V to II, that is, the faster the layer is formed, the deeper it is located. All parts of the brain where there is a layer-by-layer structure are formed in a similar way.

The nuclei in the brain are formed in the opposite way: first, more superficial layers are formed, then deeper ones.

Neurodimensional theory and genetic aspects

At the beginning of the 20th century, a neurodimensional theory was formed. Its essence lies in the fact that the primary vesicles, in turn, consist of smaller structures - neuromeres. The formation of each neuromere is an individual interaction of several genes. The neurodimensional theory is valid for all vertebrates. Topographically, rhombomeres are distinguished, that is, neuromeres of the rhombencephalon, mesomeres (middle) and prosomeres (anterior). Genes that are involved in the formation of various sections and neuromeres are called homeobox genes. Homeobox is a gene that regulates embryonic development. There are many types and classes of homeoboxes, including HOX genes, POX genes, engrailed genes, Wnt genes, Nkx genes.

Genes and the proteins they encode influence more than just the brain vesicle stages. Thus, the formation of the neural plate is impossible without the synthesis of the chordin by the prechordal mesoderm. It inhibits osteomorphic proteins (BMPs), which prevent plate formation. The role of osteomorphic proteins is not only inhibitory. They are synthesized by the dorsal plate of the neural tube and contribute to the formation of the alar plate. The ventral plate synthesizes Shh, which is responsible for the formation of the basal plate and eyes.

It should be noted that the homeobox sequence is found not only in vertebrates, but also in invertebrates (for example, Drosophila).

Cellular organization of the brain

Cellular composition

In invertebrates, the anterior ganglion contains only neurons. The vertebrate brain consists of two main types of cells: nerve cells (neurons, or neurocytes) and neuroglial cells.

Neurons in different parts of the brain have different shapes, so the neural composition of the brain is very rich: pyramidal and non-pyramidal (granular, candelabra, basket, spindle-shaped) cells of the cerebral cortex in the cerebellum contain Purkinje and Lugar cells; Golgi cells types I and II, which can be found in the nuclei. Their function is to perceive, process and transmit signals from and to various parts of the body.

Neuroglia are divided into macroglia, ependymal glia and microglia. The first two glia have a common origin with neurons. The origin of microglia is monocytic. Ependymal glia consist of ependymocytes. These cells line the ventricles of the brain and are involved in the formation of the blood-brain barrier (BBB) and the production of cerebrospinal fluid. Macroglia consists of astrocytes and oligodendrocytes. These cells provide physical support for neurons involved in the regulation of metabolism and ensure recovery processes after damage. Astrocytes are part of Hebu. Microglial cells perform a phagocytic function.

Brain cells and their processes form gray and white matter. They are named so because of the characteristic color they exhibit when opened. Gray matter consists of neuron cell bodies and is represented by the cortex and nuclei. White matter is formed from myelinated cell processes. It is the myelin that gives them their white color.

Cyto- and myeloarchitecture

Cytoarchitectonics understands the topography and relative position of the cells that form the layers and the structure of these layers. The myeloarchitecture area is the processes of nerve cells that form stripes. In the brain, areas with a layered structure are the cortex (especially the neocortex), the plate of the midbrain roof and the cerebellum. In addition to them, the nuclei located in the thickness of the white matter of the brain also have a layered structure. An example of a layer-by-layer structure is the cytoarchitecture of the neocortex, which is as follows:

the first layer is the molecular layer, which is rather poor in neurons (stellate cells and Cajal-Retzius cells) and is dominated by processes of cells of other layers
the second layer is called the outer granular layer due to the large number of granular cells in it
the third layer is the outer pyramidal layer; It also got its name from the peculiar appearance of the cells that it contains.
the fourth layer is the inner granular layer and contains granular and stellate cells
the fifth layer is the ganglion layer containing Betz cells
sixth layer - polymorphic (through a large number of different neurons)

The functional unit of the cerebral cortex is the medullary column. It is a segment in which the corticocortical fiber passes.

Also associated with cytoarchitectonics in humans and other studied animals are fields - functional zones of the cortex, associated with the performance of a certain function and have a certain cell structural structure.

Anatomy

Basic structures

Medulla

The medulla oblongata is that part of the brain that is largely similar in structure to the spinal cord. Thus, the gray matter of the medulla oblongata is formed in the form of nuclei located between the bundles of white matter. The white matter of the medulla oblongata is a variety of ascending and descending pathways that form such formations as oils, pyramids, bulbs-thalamic tract, and spinal lemniscus. The nuclei are divided into cranial nerve nuclei and vital function centers. Along the entire medulla oblongata, and up to the intermediate brain, there is a reticular formation. The fourth ventricle is located inside the medulla oblongata.

The bridge (lat. Pons) is found only in mammals (although bridge-like connections are also present in birds). Consists of a tire and a base. The tegmentum contains fibers from the cortex to the cerebellum and the spinal cord, housing the pontine nuclei. It also contains the nuclei of the cranial nerves, its own nuclei and the pneumotaxic center (part of the respiratory center). It is to the pontine nuclei that fibers from the cortex are directed and fibers extend to the contralateral half of the cerebellum. Heading towards the cerebellum, they cross the midline and unite the two opposite halves of one formation, acting as a kind of “bridge”.

Cerebellum and cerebellar structures

The cerebellum is a derivative of the alar plate, which is located above the fourth ventricle. Its development is associated with gravity receptors, the vestibular apparatus and the need to maintain balance. Although the development of the cerebellum differs among vertebrates, a standard module of its construction can still be distinguished: most often it consists of the body, or vermis, (Latin: Vermis) and the ears of the cerebellum (Latin: Auriculi cerebelli), which in tetrapods are called the flocculus (Latin: vermis). flocculus). In mammals and birds, a third section appears - the hemispheres. In most agnathans (the exception is lampreys), the cerebellum is absent. The brain reaches its best development in birds and mammals. The cerebellum consists of gray matter (cortex) and white matter (fibers); the cortex forms three layers: the superficial molecular layer, the internal granular layer and the layer of Purkinje cells, which is located between them. Three phylogenetic parts can be distinguished in it (although this division remains controversial): ancient, old and new cerebellar; the latter is present in mammals (the presence in birds remains under debate). Anatomically, the ancient cerebellum corresponds to the body (in mammals - the vermis), the old cerebellum corresponds to the ears (the flocculus and the nodules associated with the flocculus (lat. Nodulus)), the new cerebellum is called its hemispheres. There is a third section of the cerebellum - physiological. So, fibers of proprioceptive sensitivity from the spinal cord are sent to the ancient cerebellum, which is why it is called the spinocerebellum; it reacts to the force of gravity. The old cerebellum is connected to acoustic fibers and is called the cerebellum. The new cerebellum is called the pons, it receives fibers from the cerebral cortex and ensures muscle synchrony during complex movements. Also, the cerebellum takes on different shapes in different classes: for example, the body of amphibians and turtles is presented in the form of a plate, while other vertebrates are characterized by a folded shape.

The cerebellum has a special structure in bony fish, in which there are formations special to them (a cerebellar-like structure called the longitudinal ridge, cerebellar valve, lateral valve nucleus).

In some vertebrates, in addition to the canonical cerebellum, one can also find so-called cerebellar structures, which have a structure similar to the cerebellum and perform similar functions. These include the longitudinal splenium, the cerebellar crest and the lateral line lobe. The posterior vestibule of the nucleus, associated with the VIII pair of cranial nerves, has a similar cerebellar structure.

Midbrain

The midbrain, together with the medulla oblongata and the pons, forms the brain stem. It consists of a roof plate (Latin Lamina tecti) (roof (Latin Tectum)), a cover (Latin Tegmentum), cerebral legs (Latin Crura cerebri) and an isthmus (Latin Isthmus) (the question of the topographical affiliation of the isthmus is open: its belong to both the pons and the midbrain, and are recognized as a separate structure). The cerebral peduncles with the covering form the cerebral peduncles (lat. Pedunculi cerebri). Each of these regions contains specific groups of nuclei and anatomical structures. Thus, the isthmus contains the pigeon spot (an important center of vigor and tension, which is involved in the regulation of sleep and activity, a component of the reticular formation), the nucleus of the isthmus, and the nucleus of the trochlear nerve. The cover is located on the ventral side of the brain stem. It is divided by the substantia nigra (lat. Substantia nigra) into its own integument and cerebral peduncles. It also contains a large number of nuclei: the mesocerebral nucleus of the trigeminal nerve, the nuclei of the third pair of cranial nerves, the red nucleus (lat. Nucleus ruber), important for the extrapyramidal system, the longitudinal medial fasciculus (lat. Fasciculus longitudinalis medialis), the lateral ridge (lat. Torus lateralis) . The roof consists of the optic lobes (lat. Lobi optici) (in mammals - the superior tubercles) and semilunar ridges (lat. Tori semicirculari) (in mammals - the inferior tubercles). In ray-finned fish, the roof plate also has a longitudinal ridge (lat. Torus longitudinalis). Due to the presence of these tubercles, the roof is also called the chotiryhump body. This structure of the midbrain is characteristic of most vertebrates. However, the midbrain of ray-finned fish, as already mentioned, has unique formations for them, namely longitudinal and lateral ridges.

Mesh formation

The reticular formation (lat. Formatio reticularis) extends along the entire brain stem (as well as along the spinal cord). In vertebrates, it performs important functions: regulation of sleep and attention, muscle tone, coordination of movements of the head and torso, collaboration in the execution of actions, regulation of impulses (blocking them or vice versa) traveling to and from the cortex. In most vertebrates, its pathways are closely related to the terminal analyzers and are the main pathways for controlling the body; Only in mammals are the reticular tracts inferior in importance to the cortical ones. The development of various structures of the reticular formation varies within even families, but there are several common to all vertebrates. Thus, in the reticular formation, three cell columns can be distinguished: the lateral parvocellular (maloclitinny), the intermediate magnocellular (large cell) and the medial raphe column. The first column is afferent, the other two are efferent. Secondly, the reticular formation includes various groups of neurons - nuclei. In agnathans there are four of them: the lower, middle and upper reticular nuclei and the mesocerebral reticular nucleus. In other vertebrates, this division is more complicated (every year new areas are described that may belong to the formation):

the inferior reticular nucleus corresponds to the ventral, dorsal, lateral, giant cell, parvoclitine nuclei and raphe nucleus
The middle and superior reticular nuclei correspond to the inferior pontine nucleus, raphe nucleus, caudal and oral pontine nuclei, pigeon spot, cuneate nucleus
The mesocerebral reticular nucleus corresponds to the pidcuneiform nucleus

In addition to these nuclei, a region studied in mammals was called the promycinal reticular nucleus, which is a thin strip of neurons in the diencephalon. Before this, it was believed that there was no reticulate formation in the intermediate cannula. The pathways of the reticular formation are divided into two types: ascending afferents and descending efferents.

Diencephalon

The structure of the diencephalon in all vertebrates is similar and consists of four parts: the ventral and dorsal thalamus, the Epithalamus and the hypothalamus. Each of these sections contains a large number of nuclei, fibers and other anatomical formations that allow the thalamus to perform its functions: to be an important subcortical center of almost all sensitivities (except smell), to be an important “nodal station” for nerve pathways leading to the cerebral cortex, be an important autonomic and neurohumoral center. In turn, these parts have their own components:

The epithalamus (lat. Epithalamus) is the center of regulation of circadian rhythms and in most vertebrates consists of two parts - the pineal gland and the leash (lat. Habenula). Some vertebrates (jawless, some snakes) contain a third part - the parietal organ (“third eye”).

The hypothalamus (lat. Hypothalamus) is an important neurohumoral center and is associated with the pituitary gland. Also in the hypothalamus there are nipple-like bodies (lat. Corpora mammilaria), which are part of the limbic system. The preoptic zone with its nuclei and the optic chiasm (lat. Chiasma opticum) of the optic nerves are also connected to the hypothalamus.

The dorsal thalamus is the main collector of all sensory pathways leading to the telencephalon. It contains a large number (true for amniotes, anamnias have three groups of nuclei) of nuclei and nuclear groups. In all vertebrates, the dorsal thalamus can be divided into two main parts: that which is associated with the lemniscus (trigeminal, medial, spinal) and that which is associated with the pathways coming from the midbrain.

The ventral thalamus is also connected to sensory pathways (visual) as well as motor ones. In mammals, it is divided into the subthalamus (lat. Subthalamus), which includes the indefinite zone (lat. Zona icerta) and subthalamic nuclei, and the metathalamus (lat. Metathalamus), which consists of the lateral geniculate bodies and their nuclei. In non-savage amniotes it contains four to five nuclei (among them the anterior and anterior medial nuclei). There are three nuclei in the anamnium - anterior, anterioserial and intermediate nuclei.

The nomenclature of the diencephalon in humans is somewhat different. Thus, according to the latest anatomical nomenclature, five parts are distinguished: the hypothalamus, subthalamus, metathalamus, epithalamus and the thalamus itself.

Basal ganglia

The basal ganglia (for humans they also use the name “the main part of the telencephalon” (lat. Pars basalis telencephali)) are contained in the thickness of the white matter of the telencephalon. Phylogenetically and functionally, two systems are distinguished - striatal and palidar (together they form the striopallidar system). They make up the bulk of the basal ganglia. There are ventral and dorsal striopallidal complexes. The anterior complex includes the nucleus accumbens and the olfactory tubercle (anterior striatum) and the anterior palidum. The posterior complex includes the caudate nucleus with enclosure (posterior striatum) and the globus pallidus (posterior palidum). The basal nuclei also often include the amygdala nucleus (applies to mammals), the substantia nigra, and sometimes the subthalamic nucleus.

Cerebral cortex (cloak)

The cerebral cortex (lat. Cortex) is the highest center of the nervous system, which subordinates the rest of the central nervous system. Since it covers the hemispheres of the telencephalon, it is called the cloak (lat. Pallium). Topographically and genetically, there are three sections (or their homologues) that are present in all vertebrates (but with varying degrees of development, especially the neocortex): the lateral, medial and dorsal mantle. The lateral mantle is the olfactory cortex, the medial mantle is the seahorse cortex, and the dorsal mantle is the cerebral cortex. Genetic experiments on animals have shown the existence of a fourth section - the anterior one. At the moment, Insua and the phylogenetic classification of the cortex (as questioned), according to which there is an ancient cortex, or mantle, old cortex and new cortex (they are responsible for the medial, lateral and dorsal mantle). The new cloak has a six-layer neural structure (isocortex), while the old and ancient one has a three-layer neural structure (alocortex). It is worth noting that the dorsal mantle is found in all vertebrates, but not all animals cover the neocortex. In most mammals, especially primates, and, of course, in humans, the new cloak has expanded so much that the brain has developed convolutions to accommodate it. They increase the area of the cortex, while the volume of the brain fits in the skull. On the surface of the hemispheres, one can distinguish the main convolutions and those that are changing or individual. A brain with convolutions is called gyrencephalic, while a brain without convolutions is called lysencephalic. The neocortex also has a functional topic: there are motor, sensory, prefrontal and others. In humans and primates, as already mentioned, certain functional cytoarchitectonic fields have been studied.

Limbic system

The medial cloak (in this context refers to the hypocampus, which it covers) is present in all vertebrates and is associated primarily with the sense of smell. In lower vertebrates, it also receives fibers from the dorsal thalamus. However, if we talk about mammals, then the hippocampus, together with some other structures, is associated not only with reception, but also with a number of important functions: memory, motivation, memorization, emotions, sexual behavior. The system that is responsible for these functions is called limbic (from the Latin Limbus - edge). It includes the following structures: hippocampus, amygdala, mamillary bodies, parahippocampal, cingulate and dentate gyrus, nucleus accumbens, anterior group of thalamic nuclei.

Olfactory brain and olfactory bulb

The olfactory brain (lat. Rhinencephalon) is considered a phylogenetically old part of the telencephalon. In addition to directly perceiving and analyzing information related to the sense of smell, it is also associated with some important functions, especially emotional and sexual behavior (most animals rely on smell when looking for a partner for procreation). The olfactory brain includes the following structures: the olfactory nerve and the olfactory bulb, which are essentially a peripheral continuation of the brain, the olfactory gyri, the olfactory triangle, and the anterior permeated substance. The lateral mantle (paleocortex) is connected to the olfactory brain.

Other brain structures

This section lists the brain structures that are associated with the brain, necessary for its normal functioning, however, or have a different embryonic origin from the brain, or a different cellular composition:

The ventricular system is similar in all vertebrates and consists of the lateral ventricles of the telencephalon, the third ventricle in the diencephalon, the aqueduct of Silvia in the midbrain and the fourth ventricle of the hindbrain, which connects to the spinal cord canal and the subarachnoid space.
The circumventricular system is a system that controls the amount and composition of cerebrospinal fluid. The system is represented by specialized organs, the number of which varies in different classes (four to five in anamniotives, reptiles and mammals have six of these, birds have nine).
Brain tissue is the connective tissue covering of the brain in vertebrates. Fish have only one Obolon - primitive. Amphibians and reptiles already have two of them - the outer hard shell (lat. Dura mater) and the inner secondary Obolon. Birds and mammals already have three full-fledged sapwood - the outer hard one, the inner soft one (lat. Pia mater) and the intermediate pavement-like one (lat. Arachnoidea mater). Obolons also form the cisterns and sinuses of the brain.
The blood-brain barrier is a barrier between the cerebrospinal fluid and the blood, which is formed by capillary wall cells, astrocytes, macrophages, and is necessary to prevent infection from entering the brain.

Comparative anatomy

Animals without a brain

The formation of the brain was directly dependent on the complex development of the nervous system as a regulator of behavior and homeostasis. The nervous system itself is diffuse. It is a collection of neurons that are evenly distributed throughout the body and contact only neighboring neurons. Its main purpose is to perceive a stimulus (sensitive neuron) and transmit a signal to muscle cells (motoneuron). The brain is absent; its role is locally performed by the ganglia. Such a nervous system is characteristic of coelenterata.

Invertebrate brain

Flatworms (Platyhelminthes) already have a nerve thickening in the main part - a ganglion, which acts as a primitive brain, and from which nerve trunks (orthogons) extend. The development of this “brain” varies within the type itself, and even within individual classes. Thus, in various ciliated worms (Turbellaria) one can observe a low level of development of the nervous system. In some representatives of this class, the paired cerebral ganglia are small, and the nervous system is similar to that of the coelenterates. In other flatworms, the ganglia are developed and the trunks are powerful. In acoelomorphs, which are a separate, but very similar in structure to the type with flatworms, neurons do not form a ganglion. In general, three patterns can be distinguished that lead to the complication of the nervous system and subsequent cephalization:

conglomeration of neurons into ganglia and trunks, that is, a certain centralization
transformation of the anterior (cerebral) ganglion into a higher coordination center
gradual immersion of the nervous system deep into the body to protect it from damage.

In Nemertina, the nervous system is built similarly, but with some complications: two pairs of cerebral ganglia (the brain essentially consists of four parts) and the nerve trunks that extend from them. One of the pairs of ganglia is located above the other. Within the phylum, there are species with primitive development of the nervous system (in them it is located rather superficially). In more developed species, the nervous system meets the three points listed above.

In roundworms (Nemathelminthes) there are also two pairs of cerebral ganglia - the suprapharynx and the pidpharyngeal. They are interconnected by powerful commissures (nerve trunks that combine symmetrical ganglia). The nervous system, however, is not very different from the similar formation in the previous types, and is organized according to the orthogonal type. There are no changes in the structure of the brain in annelids (Annelida). But in addition to the paired cerebral ganglia, which are united by commissures, and nerve trunks, each segment has its own nerve ganglion.

In arthropods (Arthropoda), the brain reaches a high level of development, but development also varies within the phylum. In crustaceans (Crustacea) and insects (Insecta), especially social ones, it reaches very high development. In a typical arthropod brain, three parts can be distinguished: the protocerebrum, which is connected to the eyes, the deuterocerebrum, which is the olfactory center, and the tritocerebrum, which innervates the oral limbs, gives off the stomatogastric nerves and is combined with the subpharyngeal ganglion. This brain enables the complex behavior of insects. Arachnids (Arachnida) lack a deuterocerebrum. The protocerebrum contains the “mushroom bodies,” which is the highest association center.

In Onychophora, the brain is also divided into three sections.

In mollusks (Mollusca) there is an accumulation of nerve ganglia. These accumulations are especially powerful in cephalopods (Cephalopoda), where they form the peripharyngeal nerve mass. The brain of this class is the largest in size among all invertebrates. It contains white and gray matter. Cephalopods are also capable of quite complex behavior, namely the formation of conditioned reflexes.

Chordates: tunicates and tunicates

Chordates include skullless or lancelets (Cephalochordata), tunicates (Urochordata) and vertebrates (Vertebrata). The nervous system of the lancelet is a neural tube with a canal inside. In front is an extension - the brain bladder; in this region the canal is wide and round, similar to the ventricles of the vertebrate brain. The node consists of two parts: the anterior bubble and the intermediate region (English: Intercalated region). There is a thickening in the middle of the bubble. The anterior vesicle is connected to the fossa of Kjolliker (olfactory organ); two nerves extend from it, which provide sensitive innervation to the rostral part of the lancelet’s body. The organ of Hesse, a photosensitive organ, is associated with the intermediate area. In tunicates there is no brain. Only its rudiment remains - the ganglion.

Chordates: vertebrates (Vertebrata)

The brain of vertebrates contains billions more neurons than the similar brain of invertebrates. Brain development is closely related to the improvement of sensory systems and organs, which are better developed in vertebrates. Also, brain development is associated with increasingly complex behavior of living beings. In general, all vertebrates are characterized by just such a “three-component structure.”

Vertebrate brain types

There are four main branches of vertebrates (in the context of evolution): jawless fishes, cartilaginous fishes, ray-finned fishes and spadefin fishes (tetrapods belong to this branch). In each of these branches, two types of brain can occur. The first type of brain is characterized by weak migration of neurons during embryonic development, so most neurons are located in the plate at the ventricles. This type of brain is called “laminar”, or type I brain (so the neurons are placed like a plate at the ventricles). The second type is characterized by the fact that neurons actively migrate. As a result, this type of brain is large in size. This type of brain is called a “complex” brain, or Type II brain. The presence or absence of migration affects the size of the brain, the topography of the anatomical structures, but in general the module of the brain structure, anatomical structures and brain function are the same for all vertebrates.

There is also a division into two types based on morphological characteristics. Most vertebrates have a telencephalon of the so-called “concave” type; This type of brain is characterized by the growth of the hemispheres above the ventricles, that is, the nervous tissue surrounds the cavity of the ventricles. In ray-finned fish, the placement of nervous tissue and cavities is something different. The roof of their ventricles is formed by the choroid. This type of telencephalon is called “everted.” Another feature is associated with it: the homolog of the medial cape in these animals will be located laterally.

Jawless (Agnatha)

Jawless animals have a typical brain structure, with three main sections. The medulla oblongata contains important vital centers. The existing reticular formation and its nuclei, of which cyclostomes have three. The ventricular system is developed in lampreys, but is very poorly developed in hagfish. The cerebellum of all cyclostomes is present only in lampreys, but it appears only histologically and has the appearance of a ridge of gray matter. The midbrain is underdeveloped, lacking the locus coeruleus, the mesocerebral nucleus of the trigeminal nerve, the red nucleus, and the substantia nigra (but the posterior tubercle is present). All agnathans, except hagfishes, have semilunar ridges. The optic lobes were also present. In the diencephalon, it is worth noting the presence of a photosensitive parapineal organ in the Epithalamus. Hagfish lack an epiphysis. In lampreys, a dorsal thalamus is present, but its nuclei have not yet been identified; In hagfish, the fibers of the thalmus, which are directed to the midbrain, are not described. The most part of the diencephalon in lampreys is the pituitary gland, which consists of the preoptic area (characteristic of all vertebrates), the anterior and posterior hypothalamus. In hagfishes, the preoptic region contains four nuclei. Lampreys have a structure-palidary complex, but hagfishes have not yet been described. The dorsal mantle is associated with the perception of olfactory information. The hagfish does not receive fibers from the diencephalon (the last two statements have been questioned by a number of researchers who have identified fibers from the diencephalon to the telencephalon, as well as areas in the telencephalon that are associated with other types of information).

Pisces

The medulla oblongata in fish will not undergo significant changes in structure. Regarding the cerebellum, in cartilaginous fish it consists of ears and a body. A feature of their brain is a granular layer, which rather resembles a cushion, which is why it is called granular enhancement (lat. Eminentia granularis). There are two such rollers above and below and they face the cavity of the fourth ventricle. In ray-finned fish, the histological structure of the cerebellum itself varies between two options: the classic three-layer and somewhat modified in some species, when Purkinje cells are located in the cerebellar valve in the molecular layer, and the granular layer forms an increase. Anatomically, such fish have unique structures associated with the cerebellum: the cerebellar valve (lat. Valvula cerebelli), which consists of external and internal leaves, a cerebellar-like structure - a longitudinal ridge, an additional nucleus - the lateral nucleus of the valve, the caudate lobe, located ventrally along the cerebellum. One of the features worth noting in the midbrain is the presence of the semilunar carina, associated with the lateral line. A red core appears. In ray-finned fish there is no black substance. It is present in cartilaginous fish. The presence of a blue spot varies among species. Also, all fish have another catecholoid region - the posterior tubercle, which is closely connected with the substantia nigra, but belongs to the diencephalon. In addition to the epiphysis, the Epithalamus contains a parietal organ. In ray-finned fish, the hypothalamus is divided into anterior and posterior hypothalamus and contains specific nuclei characteristic of them. Specific formations in the hypothalamus are also found in cartilaginous fish (for example, the nucleus of the lateral lobe, the median nucleus). The telencephalon contains three sections of the mantle, but their topography depends on what type of brain the fish belongs to - lamellar or “inverted”. The dorsal cloak (not covered by the neocortex) is approached by fibers from the intermediate (dorsal thalamus) brain. There are 10 pairs of cranial nerves leaving the brain. From the brain arise ten pairs of “classical” cranial nerves, a photosensitive nerve in the pineal gland, a terminal nerve, and lateral line nerves.

Amphibians

The medulla oblongata is unchanged. The cerebellum, small in size, consists of a body and ears. It is characterized by a classic three-layer histological structure. In the midbrain, in addition to the standard set of nuclei (blue spot, red nucleus, serocerebral nucleus of the trigeminal nerve), there is a posterior tubercle and a semilunar ridge. Substantia nigra is absent. The epithalamus consists of the pineal gland and the photosensitive frontal organ. The dorsal thalamus has three nuclei - anterior, middle and posterior. The hypothalamus is connected to the pituitary gland and the preoptic area. The telencephalon consists of medial, lateral and dorsal sections. Fibers from the thalamus approach the dorsal cloak. The existence of a front cloak has also been experimentally proven in frogs. Existing components of the construction-palidar system.

Reptiles (Reptilia)

The structure of the medulla oblongata does not differ from the same structure in amphibians. The development of the cerebellum in reptiles is the best, in addition, the body shape is excellent: in turtles the body is flat, in alligators it is curved, and in lizards it is curved and with the opposite arrangement of layers, when the granular layer is the outer layer. The midbrain contains the locus coeruleus, the red nucleus, the mesocerebral nucleus of the trigeminal nerve, the substantia nigra appears, but its homologue, the posterior tubercle, disappears. Like all vertebrates, there is a semilunar carina, but now it is associated only with auditory stimulation. In the diencephalon of lizards and gatoras there is a parietal (parietal) eye. The dorsal thalamus contains a large number of nuclei (practically in reptiles, birds and mammals the same groups or their homologues can be found; the only thing that is different about them is different nomenclature relative to these classes of animals), to which ascending pathways come. The most prominent area that receives signals from the midbrain is the nucleus teres. The telencephalon consists of the striato-palidar complex (anterior and posterior striato-palidar complexes) and the superior (lateral, medial and posterior), which in each section has a three-layer structure. A feature of the dorsal cloak in reptiles (and birds) is the presence of a specific region with a large number of nuclei and a laminar structure - the posterior ventricular ridge. It is divided in reptiles into the anterior one, to which fibers from the thalamus are directed, and the posterior one, to which fibers from the anterior part of the splenium and, associated with Jacobson’s organ, the spherical nucleus approach. Therefore, the posterior cloak in reptiles is two-component: it consists of this roller and the bark of the posterior cloak.

Birds (Aves)

The cerebellum, the body of which contains ten folds, reaches very good development. In addition, many researchers believe that in the avian cerebellum it is acceptable to use the term “new cerebellum” (that is, the part of the cerebellum associated with the coordination of complex movements). The reticular formation contains the same nuclei as those of all other vertebrates (except jawless ones). The midbrain is also characterized by the presence of all structures typical of the amniote: the substantia nigra, the red nucleus, the blue spot, and the semilunar ridge. The thalamus contains a large number of nuclei characteristic of the amniote. The telencephalon is complex in structure, similar to the telencephalon of reptiles. The building-palidary complex is divided into front and rear. In turn, the posterior striatum is divided into lateral and medial. The cloak consists of a lateral cape, a medial cape, and two components that form the dorsal cape. These two components are the posterior ventricular carina, also found in reptiles, and the hyperpalium. The ridge in birds is divided into nidopalium, mesopalium and arcopalium. Hyperpalium (another name for Wulst) is associated with the perception of sensitive information, and also descending pathways to the underlying parts of the central nervous system begin from it.

Mammals (Mammalia)

The cerebellum receives powerful development, in which, in addition to the ears (clump) and body, the cerebellar hemispheres appear. Both the body and the hemispheres are covered with folds. In the midbrain, the optic particles and semilunar ridges are called the superior and inferior colliculi, respectively. They are closely connected with the lateral (concerns the superior colliculi) and medial (concerns the inferior colliculi) geniculate bodies; The geniculate bodies themselves are a component of the diencephalon - the metathalamus (considered by different researchers to be either a separate component of the diencephalon, or part of the forebrain). The dorsal thalamus also contains a large number of nuclei: the geniculate, anterior, posterior, lateral and medial (together they constitute the anterior group), reticularis and others. The anterior thalamus (specifically the subthalamus) also contains nuclear groups: zona indeterminate, subthalamic nucleus, Trout area. The basal ganglia include the stratopalidary complex, the amygdalabin nucleus, and the nucleus of Meynert. The cloak consists of a medial and lateral cloak (three-layer cytoarchitecture) and a new cloak covered by the neocortex (six-layer cytoarchitecture). One of the important features of the mammalian brain is the appearance of convolutions. Some gyri are specific to certain animals, but most are common to all gyrencephalic mammals (eg, postcentral gyrus, precentral gyrus, superior temporal). Also in the mammalian brain one can distinguish particles - frontal, parietal, temporal, occipital, insula, as well as the limbic lobe. Animals have a corpus callosum, which contains fibers from one half of the brain to the other.

Functions

Somatosensory system

Basic concepts and departmental cooperation

Because of feelings, every living being receives information about the environment and inner worlds. The brain is the center that analyzes this information and turns it into action.

Initially, information about the stimulus comes from the periphery - from receptors, then along nerves, ganglia and then to the central nervous system. In the central nervous system, through ascending pathways, information arrives in turn to higher and higher located departments. The main such “centers” are the diencephalon and the telencephalon. It is to the thalamus, as a “relay”, that most types of sensitivity (except smell) are directed; From the nuclei of the thalamus, the fibers of the pathways are directed to the dorsal cloak and, to a certain extent, to the basal nuclei. The cortex of the dorsal mantle (and to a lesser extent of the other mantles) is the highest center for the analysis of sensory information. In addition to the telencephalon and diencephalon, the midbrain plays an important role for the sensory system, through which important visual (for example, the retino-tectonically thalamofugal pathway in the ray-finned tract passes through the midbrain and is essentially the main visual nerve pathway), auditory fibers and fibers from side line.

Thus, the entire sensory system, through the mediation of pathways, is interconnected. For example, in the medulla oblongata (and spinal cord) there are sensory nuclei that are the first in the central nervous system to perceive information; further it goes to the thalamus; Parallel to the thalamus, the pathways of the midbrain enter, and then the fibers go to the telencephalon.

The thalamus and telencephalon can be divided into two parts, it depends on where they receive information from: lemnothalamus and lemnopalium, connected with ascending fibers from the spinal cord and trigeminal nuclei (from the Latin Lemniscus - loop, since such pathways are formed by different types loops - in the middle, trigeminal, lateral and spinal) and colothalamus with copalium, associated with fibers coming from the midbrain (from the Latin colliculus - tubercle (tubercles of the midbrain)). This type of construction is typical for all, with the exception of a slight modification in ray-finned fish and vertebrates.

Somatosensory system in various vertebrates

The sensory system in mammals has been better studied. In the telencephalon they have the somatosensory cortex (S1), which is the highest center for the analysis of tactile and pain sensitivity. Regarding the boundaries and shape of this area, it is located and structured differently in different mammals: in humans it is limited to the post-central gyrus, in the platypus it occupies a huge area of the cortex. Also, this area is characterized by somatotopic specialization, that is, a certain area analyzes information from a certain part of the body. In birds and reptiles, the cortex of their dorsal mantle is to a certain extent a homologue of the same cortex in mammals, but clear sensitive areas have not yet been found in them (except for some data on the regions responsible for the analysis of facial sensitivity in birds). The same applies to amphibians and fish: in amphibians, the fibers reach the telencephalon, but do not form clear sections. In ray-finned, spade-finned and jawless animals, fibers were also found that go to the telencephalon and which, as in the case of amphibians, do not form clear somatosensory areas in the cortex.

In addition to the cortex, somatotopic organization is also observed in the lower parts of the central nervous system. Thus, the spinal nucleus of the trigeminal nerve in humans consists of three parts, which are responsible for different parts of the face. In Condylura cristata, the main nucleus of the trigeminal nerve is divided into eleven regions, corresponding to the eleven receptor fields of the snout.

Motor system

The motor system is designed to respond to stimulation. It provides the reaction and behavior of a living being. If we talk about mammals, then according to the somatosensory system, the somatomotor system has a certain area in the cerebral cortex. There are several such areas. For primates and humans, the primary motor area is the precentral gyrus. In addition, depending on the species, additional areas may be present - an additional motor area, an anterior premotor area. It is worth saying that the precentral gyrus is also characterized by somatotopy similar to the postcentral gyrus. The corticospinal and corticobulbar tracts are directed from the cortex (in ungulates, a unique pathway for them is the Begley’s bundle, which follows ipsilaterally, and not contralaterally, like the corticobulbar tract).

According to birds, the temporo-parietal-occipital region and certain dilinks of the hyperpalium can act as an analogue of the motor area in them. The pathways from them perform similar functions to the corticospinal and corticobulbar tracts of mammals. Birds have another important tract - the occipito-mid-brain tract, which is essentially a homologue of Bagley's bundle.

According to anamnios, their motor system still requires close study. Fibers in the roof plate, fibers from the reticular formation, vestibular nuclei, which are directed to the spinal cord, were identified. Regarding the motor areas in the telencephalon, this issue requires more detailed study.

Homeostasis and endocrinology

Every living creature has a certain set of physiological and biochemical indicators that ensure its normal functioning. Under the influence of the environment and changes within the body itself, these indicators change their meaning. If they change too much, the creature may die. Homeostasis (the appropriate term is homeokinesis) is understood as the body’s ability to maintain the constancy of these indicators.

In the context of the brain, the most important area that controls many visceral functions, and therefore maintains homeostasis, is the hypothalamus. In the hypothalamus itself there are groups of nuclei that secrete active hormones; it is also anatomically combined with the pituitary gland, which secretes even more hormones. The connection between the pituitary gland and the hypothalamus is not only anatomical, but also functional and biochemical: the hypothalamus secretes releasing factors, which through the venous network (and in bony fishes and lampreys, through diffusion) enter the pituitary gland and stimulate or suppress the release of tropic hormone. A tropic hormone acts on the target tissue in which the hormone is released and directly performs a biological function (for example, adrenaline, which accelerates the heartbeat and constricts blood vessels). In addition to this direct connection, there are feedback connections that control the adequate release of hormones: with an increase in the amount of hormone, the amount of tropic hormone decreases and the amount of statin increases; when the hormone decreases, the amount of tropic hormone and liberins increases.

In the hypothalamus there are nuclei that are not associated with the production of hormones, but with welcoming functions and the support of certain indicators of homeostasis. Thus, in warm-blooded animals, the hypothalamus contains the anterior and posterior nuclei, which regulate body temperature (the anterior one is responsible for heat transfer, the posterior one is responsible for heat production). The postero- and anteromedial nuclei are responsible for feeding behavior and aggression.

The medulla oblongata contains important centers - respiratory, swallowing, salivation, vomiting, and the cardiovascular center. The defeat of these formations results in the death of the creature.

Another department that affects homeostasis to a certain extent is the pineal gland. It affects circadian rhythms through melatonin and serotonin and affects the maturation of the body.

Sleep and activity

Sleep is characteristic of almost all living beings. Evidence is provided that sleep-like states exist in Drosophila and C. elegans. Little studied (as well as its prevalence) is the sleep of fish and amphibians. For reptiles, birds and mammals, sleep is an essential period of life.

The neurophysiology of sleep is better understood in birds and mammals and is similar across these classes. There are two phases in sleep - the phases of rapid and slow sleep. The first stage is characterized by low voltage and high frequency; for the second stage - high voltage and low frequency. During REM sleep, a person can dream. It is believed that REM sleep is characteristic only of amniotes (including reptiles).

The nature of sleep is not fully understood. However, certain brain structures associated with sleep and alertness have been studied. Thus, sleep is influenced by homeostasis and circadian rhythms. The hypothalamus is the main regulator of homeostasis, and therefore affects sleep. The suprachiasmatic nucleus of the hypothalamus is one of the main controllers of circadian rhythms. Homeostasis and circadian rhythms in their interactions regulate sleep: daily activity is regulated by circadian rhythms, and, for example, blood pressure and heart rate change during sleep). An important area that acts as a sleep trigger is the preoptic area. When it was destroyed in animals, the latter lost the ability to fall asleep. Destruction of the posterior hypothalamus leads to excessive sleep.

Another important system that regulates impulses entering the cortex and hypothalamus is the reticular formation. The most important nuclei are the locus coeruleus, the oral pontine nucleus, and the inferior pontine nucleus. It is also believed that in mammals the activity of these nuclei is regulated by the thalamic reticular nucleus.

Vocalization and language

All mammals, birds, most reptiles and some amphibians are capable of making sounds, with the help of which they can communicate with their own kind, defend territory, and find a sexual partner. In humans, this ability is a necessity for full integration into society and has developed so much that it has become a language.

When we talk about language, we first understand the ability to speak, that is, oral speech. In humans, the speech center is located in the posterior third of the inferior frontal gyrus of the dominant hemisphere - this is Broca's center. A person is also capable of understanding and learning from what he hears - this is ensured by the Wernicke center. Also, the additional motor area is involved in the formation of the tongue; further, their axons are directed to the motor nuclei V, VII, XII and the double nucleus and actually influence articulation. Another important pathway, which includes the emotional component of language, follows from the cingulate cortex to the gray matter around the aqueduct in the midbrain. This center is the most important broadcast center for most mammals. In humans, it is connected with the medulla oblongata, with the pathways to the respiratory muscles and thus attracts breath in speech. For other mammals, the main sources of sounds are the supplementary motor area, the cingulate gyrus, and the above-mentioned gray matter around the aqueduct.

In birds, the area in the telencephalon responsible for sound production is the superior vocal center (in some parrots, the role of HVC is performed by other specific formations). The HVC is associated with the auditory system. Fibers from the HVC are directed to the X region and the solid core. Fibers directly from area X also approach the solid nucleus. Subsequently, the fibers are directed to two targets - part of the nucleus of the XII nerve (XIIst), which is responsible for the syrinx and to the respiratory center. In Parrot this system is complicated by specific creations, but the scheme of its construction is typical. In non-singing birds, the vocal-respiratory pathway is significantly simplified - fibers from the posterior nidopalium are directed to the arcopalium, and from there to the nuclei in the medulla oblongata.

Some frogs are also capable of making sounds. The fibers that control sound production begin in the anterior striatum. They are sent to the medulla oblongata, to the anterior trifrequency nucleus (or anterior trifrequency region; nomenclature differs in different species), and then to the motor nuclei of the cranial nerves. Some fibers are also directed from the preoptic area.

Evolution

Various theories and their criticism

One of the first theories to explain the evolutionary development of the brain belongs to Charles Judson Herrick. He believed that the brain of vertebrate predecessors was poorly divided into sections. During its historical development, the brain in further vertebrates became increasingly more complex in structure. This theory fit perfectly into the context of scala naturae and therefore became decisive for a long time.

The next question was why new departments were formed and why such departments. Paul MacLean tried to answer this with his “triune brain” theory. Since the human brain is considered developed, it is in humans that three historical and functional parts of the brain can be found: the reptile brain (English: Reptile complex, R-complex). This is the brain stem, which is responsible for basic vital functions. The second component is the brain of ancient mammals (Paleomammalian brain), which is a subpalium (basal ganglia and limbic system), therefore responsible for functions such as emotions and sexual behavior. The last section is the brain of new mammals (Latin: Neoommalian brain). It is the cortex that enables complex behavior.

Brain

In each part of the brain there is a roof, or mantle, and a bottom, or base. The roof is made up of the parts of the brain that lie above the ventricles, and the bottom is made up of the parts below the ventricles.

Thus, in all vertebrates the brain consists of five sections located in the same sequence. However, the degree of their development is not the same among representatives of different classes. These differences are due to phylogeny. There are three types of brain: ichthyopsid, sauropsid and mammalian.

Ichthyopsid type

The diencephalon of fish is covered from above by the forebrain and middle brain. A growth extends from its roof - the pineal gland; from the bottom - a funnel with the adjacent pituitary gland and optic nerves.

The medulla oblongata in fish has highly developed visceral lobes and is associated with the strong development of taste organs.

The diencephalon is clearly visible from above. Its roof is formed by an appendage - the pineal gland, and the bottom - the pituitary gland.

The midbrain is smaller in size than that of fish. The midbrain hemispheres are well defined and covered with cortex. This is the leading department of the central nervous system, because This is where the received information is analyzed and response impulses are generated. It retains the importance of the visual center.

The cerebellum is poorly developed and has the appearance of a small transverse ridge at the anterior edge of the rhomboid fossa of the medulla oblongata. Poor development of the cerebellum corresponds to simple movements of amphibians.

FISH

Forebrain small, not divided into hemispheres, has only one ventricle. Its roof does not contain nerve elements, but is formed by epithelium. Neurons are concentrated at the bottom of the ventricle in the striatum and in the olfactory lobes extending in front of the forebrain. Essentially, the forebrain functions as an olfactory center.

Midbrain is the highest regulatory and integrative center. It consists of two optic lobes and is the largest part of the brain. This type of brain, where the highest regulatory center is the midbrain, is called ichthyopsidpym.

Diencephalon consists of a roof (thalamus) and a bottom (hypothalamus). The pituitary gland is connected to the hypothalamus, and the pineal gland is connected to the thalamus.

Cerebellum in fish it is well developed, since their movements are very diverse.

Medulla without a sharp boundary it passes into the spinal cord and the food, vasomotor and respiratory centers are concentrated in it.

10 pairs of cranial nerves depart from the brain, which is typical for lower vertebrates

Amphibians

Amphibians have a number of progressive changes in the brain, which is associated with the transition to a terrestrial lifestyle, where conditions, compared to the aquatic environment, are more diverse and characterized by inconsistency of operating factors. This led to the progressive development of the sense organs and, accordingly, the progressive development of the brain.

Forebrain the amphibian is much larger in comparison with fish; it has two hemispheres and two ventricles. Nerve fibers appeared in the roof of the forebrain, forming the primary medullary vault - archipallium. The cell bodies of neurons are located in depth, surrounding the ventricles, mainly in the striatum. The olfactory lobes are still well developed.

The highest integrative center remains the midbrain (ichthyopsid type). The structure is the same as that of fish.

Cerebellum due to the primitiveness of amphibian movements, it has the shape of a small plate.

Intermediate and medulla oblongata the same as those of fish. There are 10 pairs of cranial nerves leaving the brain.

State educational institution of higher professional education "Stavropol State Medical Academy" of the Ministry of Health and Social Development of the Russian Federation

Department of Biology with Ecology

ON SOME ISSUES OF EVOLUTION

(added)

Methodological manual for 1st year students of StSMA

STAVROPOL,

UDC 57:575.

On some questions of evolution. Methodological manual for 1st year students. Publisher: StSMA. 2009 p.31.

In the textbook of biology, ed. and, which is used by 1st year students when studying medical biology and genetics, some questions of the theory of evolution require addition and clarification. The staff of the Department of Biology of St. State Medical Academy considered it necessary to compile this methodological manual on some issues of the theory of the evolution of living nature.

Compiled by: Doctor of Medical Sciences, Prof. ,

Ph.D., Associate Professor ,

Ph.D., Associate Professor

© Stavropol State

Medical Academy, 2009

PHYLOGENESIS OF ORGAN SYSTEMS IN ANIMALS

The fundamentals of the structure and function of various organs and organ systems in animals and humans cannot be sufficiently and fully understood without knowledge of their historical formation, that is, phylogenesis.

Phylogeny of the nervous system.

All living organisms experience various influences from the external environment throughout their lives, to which they respond by changing behavior or physiological functions. This ability to respond to environmental influences is called irritability.

Irritability already occurs in protozoa and is expressed in changes in their vital processes or behavior in response to stimuli such as chemical, temperature, and light.

In multicellular animals, a special system of cells appears - neurons, capable of responding to certain stimuli with a nerve impulse, which they transmit to other cells of the body. The collection of nerve cells forms the nervous system, the complexity of the structure and function of which increases with the complexity of the organization of animals. Depending on the latter, three main types of nervous system have developed in multicellular animals in evolution: reticular (diffuse), ganglion (nodular) and tubular.

Diffuse (network-like)) nervous the system is characteristic of the most primitive animals - coelenterates. Their nervous system consists of neurons distributed diffusely throughout the body, which with their processes contact each other and the cells they innervate, forming a kind of network. This type of organization of the nervous system ensures high interchangeability of neurons and thereby greater reliability of functioning. However, responses with this type of organization of the nervous system are imprecise and vague.

Nodular (ganglionic) type is the next step in the development of the nervous system. It is characteristic of all worms, echinoderms, mollusks and arthropods. They have a concentration of neuron bodies in the form of single clusters - nodes (ganglia). Moreover, in flatworms and roundworms such nodes are located only at the anterior end of the body, where the organs of food capture and sensory organs are concentrated. In annelids and arthropods, the body of which is divided into segments, except for the head ganglia, an abdominal chain of nerve ganglia is formed that regulate the functioning of the tissues and organs of a given segment (annelis) or group of segments (arthropods). However, the head ganglion, which is the coordinating and regulating center in relation to the other ganglia, always remains the most developed. This type of nervous system is characterized by some organization: where excitation passes strictly along a certain path, which gives an advantage in the speed and accuracy of the reaction. But this type of nervous system is very vulnerable.

Chordates are characterized by tubular type of nervous system. In the embryonic period, a neural tube is formed from the ectoderm above the notochord, which in the lancelet remains throughout life and serves as the central part of the nervous system, and in vertebrates it is transformed into the spinal cord and brain. In this case, the brain develops from the anterior part of the neural tube, and from the rest of it - the spinal cord.

The brain in vertebrates consists of five sections: the forebrain, the intermediate midbrain, the medulla oblongata and the cerebellum.

EVOLUTION OF THE BRAIN IN VERTEBRATES

Fish

Diencephalon consists of a roof (thalamus) and a bottom (hypothalamus). The pituitary gland is connected to the hypothalamus, and the pineal gland is connected to the thalamus.

Cerebellum in fish it is well developed, since their movements are very diverse.

Medulla without a sharp boundary it passes into the spinal cord and the food, vasomotor and respiratory centers are concentrated in it.

10 pairs of cranial nerves depart from the brain, which is typical for lower vertebrates.

Amphibians

Amphibians have a number of progressive changes in the brain, which is associated with the transition to a terrestrial way of life, where conditions, compared to the aquatic environment, are more diverse and are characterized by the variability of operating factors. This led to the progressive development of the senses and, accordingly, the progressive development of the brain.

The highest integrative center remains the midbrain (ichthyopsid type). The structure is the same as that of fish.

Cerebellum due to the primitiveness of amphibian movements, it has the shape of a small plate.

Intermediate and medulla oblongata the same as those of fish. There are 10 pairs of cranial nerves leaving the brain.

Reptiles (reptiles)

Reptiles belong to higher vertebrates and are characterized by a more active lifestyle, which is combined with the progressive development of all parts of the brain.

Forebrain is the largest section of the brain. Developed olfactory lobes extend in front of it. The roof remains thin, but islands of cortex appear on the medial and lateral sides of each hemisphere. The bark has a primitive structure and is called ancient - archeocortex. The role of the higher integrative center is performed by the striatal bodies of the forebrain - sauropsid type brain. The striatum provides analysis of incoming information and the development of responses.

Intermediate, brain, being connected to the pineal gland and pituitary gland, it also has a dorsal appendage - a parietal organ that perceives light stimulation.

Midbrain loses its significance as a higher integrative center, and its significance as a visual center also decreases, and therefore its size decreases.

Cerebellum much better developed than in amphibians.

Medulla forms a sharp bend, characteristic of higher vertebrates, including humans.

12 pairs of cranial nerves depart from the brain, which is typical for all higher vertebrates, including humans.

Birds

The nervous system, due to the general complexity of its organization, adaptability to flight and living in a wide variety of environments, is much better developed than that of reptiles.

During the day, birds are characterized by a further increase in the total volume of the brain, especially the forebrain.

Forebrain at birds are the highest integrative center. Its leading department is the striatum (sauropsid type of brain).

The roof remains poorly developed. It preserves only the medial islands of the cortex, which serve as the highest olfactory center. They are pushed towards the junction between the hemispheres and are called the hippocampus. The olfactory lobes are poorly developed.

Diencephalon small in size and associated with the pituitary gland and pineal gland.

Midbrain has well-developed optic lobes, which is due to the leading role of vision in the life of birds.

Cerebellum large, has a middle part with transverse grooves and small lateral outgrowths.

Oblong Mot the same as in reptiles. 12 pairs of cranial nerves.

Mammals

Forebrain - this is the largest part of the brain. In different species, its absolute and relative sizes vary greatly. The main feature of the forebrain is the significant development of the cerebral cortex, which collects all sensory information from the senses, produces a higher analysis and synthesis of this information and becomes an apparatus for subtle conditioned reflex activity, and in highly organized mammals - also for mental activity ( maternal type of brain).

In the most highly organized mammals, the cortex has grooves and convolutions, which significantly increases its surface.

The forebrain of mammals and humans is characterized by functional asymmetry. In humans, it is expressed in the fact that the right hemisphere is responsible for imaginative thinking, and the left hemisphere for abstract thinking. In addition, the centers of oral and written speech are located in the left hemisphere.

Diencephalon contains about 40 cores. Special nuclei of the thalamus process visual, tactile, taste and interoceptive signals, then sending them to the corresponding areas of the cerebral cortex.

The hypothalamus contains higher autonomic centers that control the functioning of internal organs through nervous and humoral mechanisms.

IN midbrain The colliculus is replaced by the quadrigeminal. Its anterior colliculi are visual, while the posterior colliculi are associated with auditory reflexes. In the center of the midbrain there is a reticular formation, which serves as a source of ascending influences that activate the cerebral cortex. Although the anterior lobes are visual, the analysis of visual information is carried out in the visual zones of the cortex, and the midbrain mainly controls the eye muscles - changes in the lumen of the pupil, eye movements, tension of accommodation. In the posterior hills there are centers that regulate the movements of the ears, the tension of the eardrum, and the movement of the auditory ossicles. The midbrain is also involved in the regulation of skeletal muscle tone.

Cerebellum has developed lateral lobes (hemispheres), covered with bark, and a worm. The cerebellum is connected with all parts of the nervous system related to the control of movements - with the forebrain, brain stem and vestibular apparatus. It ensures coordination of movements.

Medulla. In it, on the sides there are bundles of nerve fibers going to the cerebellum, and on the lower surface there are elongated ridges, called pyramids.

There are 12 pairs of cranial nerves originating from the base of the brain.

PHYLOGENESIS OF THE CIRCULATORY SYSTEM

In multicellular organisms, cells lose direct contact with the environment, which creates the need for a fluid transport system to deliver necessary substances to the cells and remove waste products. In lower invertebrates (sponges, coelenterates, flatworms and roundworms), the transport of substances occurs by diffusion of tissue fluid currents. In more highly organized invertebrates, as well as in chordates, vessels appear that provide circulation of substances. The circulatory system appears, then the lymphatic system. Both develop from mesoderm.

Evolutionarily, two types of circulatory system have developed: closed and open. In the closed one, blood circulates only through the vessels, and in the open part of the path it passes through slit-like spaces - lacunae and sinuses.

The circulatory system first appears in annelids. She is closed. There is no heart yet. There are two main longitudinal vessels - abdominal and dorsal, connected to each other by several annular vessels running around the intestine. Smaller vessels depart from the main vessels to the organs; blood flows forward through the spinal vessel, and backward through the abdominal vessel.

In arthropods, the circulatory system reaches a higher organization. They have a central pulsating apparatus - the heart, it is located on the dorsal side of the body. When it contracts, blood enters the arteries, from where it pours into the slit-like spaces between the organs (sinuses and lacunae), and then is reabsorbed through the paired openings in the heart, then the circulatory system arthropods are not closed.

In insects, blood does not perform the function of transporting gases; it is usually colorless and is called hemolymph.

Mollusks also have an open circulatory system, but in addition to arteries, they also have venous vessels. The heart has several atria, into which veins flow, and one large ventricle, from which arteries arise.

In the most primitive chordate animals, the lancelet, the circulatory system is in many ways reminiscent of the vascular system of annelids, which indicates their phylogenetic relationship. The lancelet does not have a heart; its function is performed by the abdominal aorta. Venous blood flows through it, which enters the gill vessels, is enriched with oxygen, and then goes to the dorsal aorta, which carries blood to all organs. Venous blood from the anterior part of the body is collected in the anterior, and from the posterior - in the posterior cardinal veins. These veins merge into the ducts of Cuvier, through which blood enters the abdominal aorta.

In the evolution of vertebrates, the appearance of a heart located on the thoracic side of the body and the complication of its structure from two-chambered to four-chambered are observed. So in fish, the heart consists of one atrium and one ventricle, venous blood flows in it. There is only one circulation and the blood does not mix. The blood circulation is in many ways similar to the circulatory system of the lancelet.

In terrestrial vertebrates, in connection with the acquisition of pulmonary respiration, a second circle of blood circulation develops and the heart, in addition to venous blood, begins to receive arterial blood. In this case, the vascular system is differentiated into circulatory and lymphatic.

An intermediate stage in the development of the circulatory system from lower to higher vertebrates is occupied by the circulatory system of amphibians and reptiles. These animals have two circles of blood circulation, but mixing of arterial and venous blood occurs in the heart.

Complete separation of arterial and venous blood is characteristic of birds and mammals, which have a four-chambered heart. Of the two aortic arches characteristic of amphibians and reptiles, only one remains: in birds it is the right one, and in mammals it is the left one.

Evolution of arterialarc.

In the embryos of all vertebrates, an unpaired abdominal aorta is formed in front of the heart, from which arterial arches arise. They are homologous to the arterial arches of the lancelet. But their number is less than that of the lancelet: in fish there are 6-7 pairs, and in terrestrial vertebrates there are 6 pairs.

The first two pairs in all vertebrates experience reduction. The following pairs of arterial arches in fish are divided into afferent and efferent gill arteries, and in terrestrial animals they undergo strong transformations. Thus, the carotid arteries are formed from the 3rd pair of arches. The fourth pair is transformed into aortic arches, which develop symmetrically in amphibians and reptiles. In birds, the left arch atrophies and only the right one is preserved. In mammals, the right arch is reduced and only the left is preserved.

The fifth pair of arches is reduced in all vertebrates and only in caudate amphibians a small duct remains from it. The sixth arch loses connection with the dorsal aorta, and the pulmonary arteries originate from it. The vessel that connects the pulmonary artery with the dorsal aorta during embryonic development called botallov duct. In adulthood, it is preserved in tailed amphibians and some reptiles. As a developmental defect, this duct may persist in other more highly organized animals and humans.

The lymphatic system is in close connection with the circulatory system: Lymph plays an important role in metabolism, since it is an intermediary between blood and tissue fluid. In addition, it is rich in leukocytes, which play an important role in immunity.

DEVELOPMENTHEARTS

In human embryogenesis, a number of phylogenetic transformations of the heart are observed, which is important for understanding the mechanisms of development of congenital heart defects.

In lower vertebrates (fish, amphibians), the heart is located under the pharynx in the form of a hollow tube. In higher vertebrates and humans, the heart is formed in the form of two tubes widely spaced from each other. Later they come closer together, moving under the intestine, and then close, forming a single tube located in the middle.

In all vertebrates, the anterior and posterior parts of the tube give rise to large vessels. The middle part begins to grow quickly and unevenly, forming an S-shape. After this, the back of the tube moves to the dorsal side and forward, forming the atrium. The front part of the tube does not move, its walls thicken and it transforms into a ventricle.

Fish have one atrium, but in amphibians it is divided in two by a growing septum. Fish and amphibians have one ventricle, but in the ventricle of amphibians there are muscular outgrowths (trabeculae) that form small parietal chambers. In reptiles, an incomplete septum forms in the ventricle, growing from bottom to top.

In birds and mammals, the ventricle is divided into two halves - right and left.

During embryogenesis in mammals and humans, there is initially one atrium and one ventricle, separated from each other by an interception with a canal connecting the atrium to the ventricle. Then, a septum begins to grow in the atrium from front to back, dividing the atrium into two parts - left and right. At the same time, outgrowths begin to grow on the dorsal and ventral sides, which are connected by two openings: right and left. Later, valves form in these holes. The interventricular septum is formed from various sources.

Violation of cardiac embryogenesis can be expressed in the absence or incomplete fusion of the interatrial or interventricular septum. Of the anomalies of vascular development, the most common is a patent ductus botellus (from 6 to 22% of all congenital malformations of the cardiovascular system), and less often - a patent carotid duct. In addition, instead of one aortic arch, two may develop - left and right, which form an aortic ring around the trachea and esophagus. With age, this ring can narrow and swallowing is impaired. Sometimes transposition of the aorta occurs, when it starts not from the left ventricle, but from the right, and the pulmonary artery - from the left.

EVOLUTION OF THE ENDOCRINE SYSTEM

Coordination of the work of organs and organ systems in animals is ensured by the presence of two closely related types of regulation - nervous and humoral. Humoral - is more ancient and is carried out through the liquid media of the body with the help of biologically active substances secreted by the cells and tissues of the body in the process of metabolism

As animals evolved, a special apparatus for humoral control was formed - the endocrine system, or the system of endocrine glands. Since the advent of the latter, nervous and humoral regulation have functioned in close interrelation, forming a single neuroendocrine system.

Hormonal regulation, unlike nervous regulation, is aimed primarily at slowly occurring reactions in the body, therefore it plays a leading role in the regulation of formative processes: growth, metabolism, reproduction and differentiation.

In invertebrates, endocrine glands first appear in annelids. The most well studied endocrine glands are in crustaceans and insects. As a rule, the endocrine glands in these animals are located at the anterior end of the body. U crustaceans There are Y-organs that cause molting. These glands are under the control of the X-organs, which are functionally closely connected with the head nerve ganglia. In addition to these glands, crustaceans have sinus glands in their eyestalks that regulate the processes of metamorphosis.

U insects At the anterior end of the body there are endocrine glands that control metamorphosis and stimulate energy metabolism. These glands are controlled by the cephalic endocrine gland, and the latter by the cephalic ganglion. Thus, the endocrine system of crustaceans resembles in its hierarchy the hypothalamic-pituitary system of vertebrates, where the pituitary gland regulates the work of all endocrine glands and is itself under the regulatory influence of the diencephalon.

Endocrine glands vertebrates play a more important role in the regulation of organ systems than in invertebrates. In addition to six separate endocrine glands (pituitary gland, adrenal gland, thyroid gland, parathyroid glands, thymus, pineal gland), hormones are produced in a number of organs that have other functions: gonads, pancreas, some cells of the gastrointestinal tract, etc. .

Endocrine glands in vertebrates in phylogeny develop from different sources and have different locations. So thyroid the gland is formed from the epithelium of the ventral side of the pharynx. In fish, it is located between the first and second gill slits, and in other vertebrates, between the second and third gill pouches. Moreover, at first this gland is laid down as an external secretion gland. During phylogenesis in a number of vertebrates, the thyroid gland changes its location, and, starting with amphibians, lobes and an isthmus appear in it, which is not typical for fish, where it looks like a single cord.

Thymus (thymus) in fish it develops due to epithelial projections that form on the walls of all gill pouches. These projections later lace up and form two narrow strips consisting of lymphoid tissue, with a lumen inside.

In amphibians and reptiles, the number of rudiments from which the thymus develops is significantly reduced - they originate from the second and third pairs of gill pouches. In mammals - from three pairs of gill pouches, but mainly from the second pair.

Pituitary in terrestrial vertebrates it consists of three lobes: anterior, middle (intermediate) and posterior; and in fish - only from the front and middle.

The pituitary gland is connected to the lower surface of the diencephalon and develops from different sources, the anterior and middle lobes from the epithelium of the roof of the oral cavity, and the posterior lobe from the distal part of the infundibulum of the diencephalon (neural origin). The function of the pituitary gland in fish is only to produce gonadotropic hormones (stimulating the production of sex hormones by the gonads). Amphibians develop a posterior lobe, which is explained by their transition to a terrestrial lifestyle and the need to regulate water metabolism. The axons of neurosecretory neurons of the hypothalamus enter the posterior lobe and the antidiuretic hormone secreted by them accumulates and subsequently enters the blood.

The middle lobe, starting from amphibians, loses the ability to produce gonadotropic hormone, and now produces a hormone that stimulates melanin synthesis. In terrestrial vertebrates, the anterior lobe, in addition to gonadotropin, secretes other tropic hormones, as well as growth hormone.

Adrenal glands in chordates they develop from two sources. Their cortex is formed by the epithelium of the peritoneum, and the medulla is of neural origin. Moreover, in fish, the cortical substance is located along the dorsal surface of the primary kidneys metamerically and separately from each other, and the medulla is located near the genital ridges on both sides of the mesentery

In amphibians, a spatial connection arises between the adrenal bodies, and in amniotes, all the adrenal anlages merge, forming a paired organ consisting of an outer cortex and an inner medulla. The adrenal glands are located above the upper pole of the kidneys.

EVOLUTION OF THE IMMUNE SYSTEM

The immune system protects the body from the penetration of genetically foreign bodies: microorganisms, foreign cells, foreign bodies, etc. Its action is based on the ability to distinguish the body’s own structures from genetically foreign ones, eliminating the latter.

In evolution, three main forms of immune response were formed: 1) phagocytosis, or nonspecific destruction of genetically foreign material; 2) cellular immunity, based on its specific recognition and destruction by T lymphocytes; 3) humoral immunity, carried out by transforming B-lymphocytes into plasma cells and their synthesis of antibodies (immunoglobulins).

In evolution, there are three stages in the formation of an immune response:

- quasi-immune(Latin “quasi” - like) recognition by the body of its own and foreign cells. This type of reaction is observed from coelenterates to mammals. With this response, immune memory is not formed, that is, there is no strengthening of the immune response to the repeated penetration of foreign material;

P primitive cellular immunity found in annelids and echinoderms. It is provided by coelomocytes - cells of the secondary body cavity that are capable of destroying foreign material. At this stage, immunological memory appears;

- system of integrated cellular and humoral immunity. It is characterized by specific humoral and cellular reactions to foreign bodies, the presence of lymphoid immune organs, and the formation of antibodies. This type of immune system is not typical for invertebrates.

Cyclostomes are already capable of forming antibodies, but the question of whether they have a thymus gland as the central organ of immunogenesis is still open. The thymus is first discovered in fish.

The thymus, spleen, and individual accumulations of lymphoid tissue are found in full, starting with amphibians. In lower vertebrates (fish, amphibians), the thymus gland actively secretes antibodies, which is not typical for birds and mammals.

A peculiarity of the immune system of the immune response of birds is the presence of a special lymphoid organ - the bursa of Fabricius. In this organ, B lymphocytes, after antigenic stimulation, are able to transform into plasma cells that produce antibodies.

In mammals, the immune system organs are divided into 2 types: central and peripheral. In the central organs of immunogenesis, the maturation of lymphocytes occurs without the influence of antigens. In the peripheral organs of immunogenesis, antigen-dependent T and B occur - the reproduction and differentiation of lymphocytes.

In the early stages of embryogenesis, lymphatic stem cells migrate from the yolk sac to the thymus and red bone marrow. After birth, the source of stem cells is the red bone marrow. Peripheral lymphoid organs are: lymph nodes, spleen, tonsils, intestinal lymphoid follicles. At the time of birth, they are still practically unformed and the reproduction and differentiation of lymphocytes in them begins only after antigenic stimulation of T- and B-lymphocytes that have migrated from the central organs of immunogenesis.

EVOLUTION OF THE RESPIRATORY SYSTEM.

Almost all living organisms are aerobes, that is, air breathers. The set of processes that ensure the intake and consumption of O2 and the release of CO2 is called respiration.

The respiratory function is ensured differently in animals of different degrees of organization. The simplest form of respiration is the diffusion of gases through the walls of a living cell (in unicellular organisms) or through the integument of the body (coelenterates; flat, round and annelid worms). Diffuse respiration is also found in small arthropods that have a thin chitinous cover and a relatively large body surface.

As the organization of animals becomes more complex, a special respiratory system is formed; So already in some water rings primitive respiratory organs appear - external gills (epithelial outgrowths with capillaries), while the skin also participates in respiration. In arthropods, the respiratory organs have a more complex structure and are represented in aquatic forms by gills, and in terrestrial and secondary aquatic forms by lungs and trachea (in the most ancient arthropods, such as scorpions, lungs, in spiders, both lungs and trachea, and in insects, higher arthropods - only trachea).

The function of the respiratory organs in lower chordates (lancelets) is taken over by the gill slits, along the partitions of which the gill arteries (100 pairs) pass. Since there is no division of arteries into capillaries in the gill septa, the total surface area for O2 supply is small and oxidative processes occur at a low level. Accordingly, the lancelet leads a sedentary lifestyle.

In connection with the transition vertebrates To an active lifestyle, progressive changes occur in the respiratory organs. So, in fish in the gill filaments, in contrast to the lancelet, an abundant network of blood capillaries appears, their respiratory surface increases sharply, so the number of gill slits in fish is reduced to four.

Amphibians- the first animals to come onto land, which developed atmospheric respiration organs - lungs (from the protrusion of the intestinal tube). Due to the primitiveness of the structure (the lungs are bags with thin cellular walls), the amount of oxygen entering through the lungs satisfies the body’s need for it by only 30-40%, therefore the skin, which contains numerous blood capillaries (dermal capillaries), also takes part in breathing. pulmonary respiration).

The airways of amphibians are poorly differentiated. They are connected to the oropharynx by a small laryngeal-tracheal chamber.

In reptiles In connection with the final exit to land, the respiratory system becomes further complicated: Skin respiration disappears, and the respiratory surface of the lung sacs increases, due to the appearance of a large number of branched partitions in which blood capillaries pass. The airways also become more complicated: cartilaginous rings form in the trachea, dividing, it gives rise to two bronchi. The formation of intrapulmonary bronchi begins.

In birds A number of features appear in the structure of the respiratory organs. Their lungs have numerous partitions with a network of blood capillaries. From the trachea comes the bronchial tree, ending in bronchioles. Part of the main and secondary bronchi extends beyond the lungs and forms cervical, thoracic and abdominal pairs of air sacs, and also penetrates the bones, making them pneumatic. During the flight, the blood is saturated with oxygen both during the act of inhalation and exhalation (double breathing).

Mammals They have lungs with an alveolar structure, due to which their surface is 50-100 times larger than the surface of the body. The bronchi are tree-like branched and end in thin-walled bronchioles with clusters of alveoli, densely intertwined with blood capillaries. The larynx and trachea are well developed.

Thus, the main direction of the evolution of the respiratory system is to increase the respiratory surface, complicate the structure of the airways, and their separation from the respiratory tract.

EVOLUTION OF THE EXCRETORY SYSTEM

In unicellular animals and coelenterates, the processes of releasing toxic metabolic products are carried out by diffusion from cells to the extracellular environment. However, already in flatworms a system of tubules appears that perform excretory and osmoregulatory functions. These tubules are called protonephridia. They begin with a large stellate cell, in the cytoplasm of which there is a tubule with a bunch of cilia that create a fluid flow. These cells carry out active transport and osmosis of water and dissolved harmful substances into the lumen of the cytoplasmic tubule.

The excretory system in roundworms is also fundamentally protonephridial in nature.

In annelids, the organs of excretion and osmoregulation are metanephridia. These are tubules, one end of which is expanded in the form of a funnel, surrounded by cilia and facing the body cavity, and the other end opens on the surface of the body with an excretory pore. The fluid secreted by the tubules is called urine. It is formed by filtration - selective reabsorption and active secretion from the fluid contained in the body cavity. The metanephridial type of excretory system is also characteristic of the kidneys of mollusks.

In arthropods, the excretory organs are either modified metanephridia or Malpighians vessels, or specialized glands

The Malpighian vessels are a bundle of tubes, one end of which ends blindly in the body cavity and absorbs excretory products, and the other opens into the intestinal tube.

The evolution of the excretory system of chordates is expressed in the transition from the nephridia of lower chordates to special organs - the kidneys

The lancelet has an excretory system similar to that of annelids. It is represented by 100 pairs nephridium, one end of which faces the secondary body cavity and absorbs excretory products, and the other removes these products into the peribranchial cavity.

The excretory organs of vertebrates are paired buds. In lower vertebrates (fish, amphibians), two types of kidneys are formed during embryogenesis: preference(or head kidney) and trunk (or primary). The preference is similar in structure to metanephridia. It consists of convoluted tubules, funneled into the body cavity, and the other end flowing into the common canal of the kidney. Not far from each funnel there is a vascular glomerulus, which filters metabolic products into the body cavity. This type of kidney functions only in the larval period, and then the primary kidney begins to function. In it, along the renal tubules, there are protrusions in which vascular glomeruli are located and urine is filtered. Funnels lose their functional significance and become overgrown.

In higher vertebrates, three kidneys are formed successively in the embryonic period: preference, primary(torso) and secondary (pelvic) kidney. The kidney is not functioning. The primary kidney functions only during embryogenesis. Its duct splits into two: Wolffian and Müllerian canals. Subsequently, the Wolffian canals are transformed into ureters, and in males into ureters and vas deferens. The Müllerian canals are preserved only in females, transforming into oviducts. That is, in embryogenesis, the urinary and reproductive systems are connected.

Towards the end of the embryonic period, the pelvic (secondary) kidney begins to function. These are compact paired formations located on the sides of the lumbar spine. The morpho-functional unit in them is the nephron, which consists of a capsule with a vascular glomerulus of a system of convoluted tubules of the first and second order and the loop of Henle. The nephron tubules become collecting ducts, which open into the renal pelvis.

EVOLUTION OF THE IMMUNE SYSTEM

The immune system protects the body from the penetration of genetically foreign bodies into the body: microorganisms, viruses, foreign cells, foreign bodies. Its action is based on the ability to distinguish its own structures from genetically foreign ones, eliminating them.

In evolution, three main forms of immune response have emerged:

1) phagocytosis - or nonspecific destruction of genetically foreign

material;

2) cellular immunity, based on the specific recognition and destruction of such material by T lymphocytes;

3) humoral immunity, carried out by the formation of immunoglobulins by the descendants of B-lymphocytes, the so-called plasma cells, and the binding of foreign antigens by them.

In evolution, there are three stages in the formation of an immune response:

Stage I - quasi-immune (Latin quasi - like, as if) recognition by the body of its own and foreign cells. This type of reaction is observed from coelenterates to mammals. This reaction is not associated with the production of immune bodies, and immune memory is not formed, that is, there is no strengthening of the immune response to the repeated penetration of foreign material.

Stage II - primitive cellular immunity is found in annelids and echinoderms. It is provided by coelomocytes - cells of the secondary body cavity capable of destroying foreign material. At this stage, immunological memory appears.

Stage III - a system of integrated cellular and humoral immunity. It is characterized by specific humoral and cellular reactions to foreign bodies. Characterized by the presence of lymphoid immune organs and the formation of antibodies. This type of immune system is not typical for invertebrates.

Cyclostomes are capable of forming antibodies, but the question of whether they have a thymus gland as the central organ of immunogenesis is still open. The thymus is first discovered in fish.

The evolutionary precursors of mammalian lymphoid organs - the thymus, spleen, accumulations of lymphoid tissue are found in full in amphibians. In lower vertebrates (fish, amphibians), the thymus gland actively secretes antibodies, which is not typical for birds and mammals.

Features of the immune response system birds consists in the presence of a special lymphoid organ - Fabrician bag. This organ produces B lymphocytes, which, after antigenic stimulation, are able to transform into plasma cells and produce antibodies.

U mammals The organs of the immune system are divided into two types: central and peripheral. In the central organs, the maturation of lymphocytes occurs without significant influence of antigens. The development of peripheral organs, on the contrary, directly depends on the antigenic effect - only upon contact with the antigen do the processes of proliferation and differentiation of lymphocytes begin in them.

The central organ of immunogenesis in mammals is the thymus, where T lymphocytes are formed, as well as the red bone marrow, where B lymphocytes are formed.

In the early stages of embryogenesis, lymphatic stem cells migrate from the yolk sac to the thymus and red bone marrow. After birth, the source of stem cells is the red bone marrow.

Peripheral lymphoid organs are: lymph nodes, spleen, tonsils, intestinal lymphoid follicles. At the time of birth, they are not yet practically formed and the formation of lymphocytes in them begins only after antigenic stimulation, after they are populated with T and B lymphocytes from the central organs of immunogenesis.

PHYLOGENESIS OF THE VISCERIAL SKULL IN VERTEBRATE ANIMALS.

The vertebrate skull consists of two main sections - axial and visceral.

1. Axial - cranium (cerebral skull - neurocranium) - a continuation of the axial skeleton, serves to protect the brain and sensory organs.

2. Visceral - facial (splanchnocranium), forms a support for the anterior part of the digestive tract.

Both parts of the skull develop independently of each other, in different ways. The visceral part of the skull in embryos of vertebrates consists of metamerically located cartilaginous arches that cover the anterior part of the digestive tract, and are separated from each other by visceral slits. The arches are designated by serial numbers in accordance with their location in relation to the skull.

The first arch in most modern vertebrates acquires the function of the jaw apparatus - it is called the maxillary, and the second - also according to its function - hyoid or hyoid. The rest, starting from the third and up to the seventh, are called gills, because they serve as a support for the gill apparatus. In the early stages of development, the visceral and axial skull are not connected to each other; later this connection arises.

Common to all vertebrate embryos, the anlage of the seven visceral arches during embryonic development undergoes various specific changes in representatives of different classes, respectively.

I. Inferior fish (cartilaginous) - Chondrichthyes

The 1st, also known as the jaw arch, consists of two large cartilages, elongated in the anteroposterior direction: the upper - palatal quadrate - the primary upper jaw, the lower - Meckel's - the primary lower jaw; they are fused to each other at the back and perform the function of the primary jaw.

The 2nd, also known as the hyoid or hyoid arch, consists of the following components:

1) from two located at the top of the hyomandibular cartilages, which are connected from above to the cranium, below - to the hyoid, and in front - to the jaw arch - the primary upper jaw;

2) from two hyoids located below the hyomandibular cartilages, which are connected to them; in addition, the hyoids are connected to the primary lower jaw;

3) from an unpaired copula (a small cartilage connecting both hyoids to each other).

Based on the location of the hyomandibular cartilage, it is clear that it plays the role of a suspension connecting the jaw arch to the skull. This type of joint is called hyostyly, and the skull is hyostyle. This is characteristic of lower vertebrates - all fish.

The remaining visceral arches from the third to the seventh form a support for the respiratory apparatus.

II.Higher fish - (bony)Osteichthyes.

The main difference concerns only the jaw arch:

1) the upper element of the jaw arch (upper jaw) consists, instead of one large palatine quadrate cartilage, of five elements - the palatine cartilage, the quadrate bone and three pterygoid cartilages;

2) in front of the primary upper jaw, two large overhead bones are formed, equipped with large teeth - these bones become the secondary upper jaws;

3) the distal end of the primary lower jaw is also covered by a large dentary bone, which projects far forward and forms the secondary lower jaw. The hyoid arch retains its previous function, i.e. the skull remains hypostyle.

III.Amphibians -Amphibia.

The main difference is in the new method of connecting the jaw arch with the skull: the palatine cartilage of the primary upper jaw fuses throughout its entire length with the axial skull, i.e., with the cranium. This type of connection is called autostyle.

The mandibular section is connected to the maxillary section and also receives a connection with the skull without a hyoid arch.

Thus, the hyomandibular cartilage is freed from the function of suspension, is significantly reduced and acquires a new function - it is part of the air cavity of the middle ear in the form of an auditory ossicle - a column.

Part of the hyoid arch (hyoid cartilage), the branchial arches form a partial support for the tongue and the hyoid apparatus, partly the laryngeal cartilages are partially reduced.

IV.Reptiles -Reptilia.

The skull is autostyle, but at the same time the palatine cartilage of the primary jaw is reduced and only the quadrate bone participates in the articulation of the upper jaw to the skull; the lower jaw is connected to it and thus joins the skull. The rest of the visceral skeleton forms the hyoid apparatus, which consists of the body of the hyoid bone and three pairs of processes.

V.Mammals -Mammalia.

A completely new way of connecting to the skull of the lower jaw appears, which attaches directly to it, forming a joint with the squamosal bone of the skull, which allows not only to grasp food, but also to perform complex chewing movements. Only the secondary lower jaw participates in the formation of the joint. Consequently, the quadrate bone of the primary maxilla loses its function as a suspension and turns into an auditory ossicle - an incus.

During embryonic development, the primary lower jaw completely leaves the lower jaw and is transformed into the next auditory bone - the malleus.

The upper part of the hyoid arch, a homolog of the hyomandibular cartilage, is transformed into a stapes.

All three auditory ossicles form a single functional chain.

1st - branchial arch (1st visceral) and copula give rise to the body of the hyoid bone and its posterior horns.

The 2nd and 3rd branchial arches (4th and 5th visceral) give rise to the thyroid cartilage, which first appears in mammals.

The 4th and 5th branchial arches (1st and 7th visceral) provide material for the remaining laryngeal cartilages, and possibly for the tracheal cartilages.

EVOLUTION OF THE DENTAL SYSTEM

AND ORAL GLANDS OF VERTEBRATES

Fish-Pisces

The dental system is homodont (teeth are the same). The teeth are conical in shape, facing backwards, serve to hold food, are located along the edge of the skull, and in some cases, on the entire surface of the oral cavity.

There are no salivary glands in the oral cavity, because they swallow food with water. The tongue is primitive, in the form of a double fold of mucous membrane. The roof of the oral cavity is formed by the base of the skull - the primary hard palate. The mouth opening is surrounded by folds of skin - lips, which are motionless. General oropharyngeal cavity.

The placoid scales of cartilaginous fish are a plate with a spine placed on it. The plate lies in the corium; the apex of the spine protrudes through the epidermis. The entire scale consists of dentin formed by corium cells; the tip of the spine is covered with enamel formed by cells of the basal layer of the epidermis.

Larger and more complex placoid scales are located in the jaws, forming teeth. In essence, the teeth of all vertebrates are modified placoid scales of their ancestors.

Amphibians - Amphibia.

Dental system homodont. The teeth of a number of amphibians are located not only on the alveolar arch; they, like fish, are characterized polyphyodontism.

Salivary glands appear, the secretion of which does not contain enzymes. The tongue contains muscles that determine its own mobility. The roof of the oral cavity is also the primary hard palate. The lips are motionless. General oropharyngeal cavity.

Reptiles- Reptilia.

Dental system in modern reptiles homodont, Poisonous reptiles have special teeth through which poison flows into the bite wound. The teeth are arranged in one row. Some extinct forms show initial differentiation. Characteristic of all reptiles polyphyodontism.

The salivary glands are better developed; among them are the sublingual, dental and labial. The secretion of the glands already contains enzymes.

In venomous snakes, the posterior pair of dental glands are transformed into poisonous ones; the secretion contains toxins (poison).

The tongue is formed from three rudiments: one - unpaired and two - paired, lying in front of the unpaired one. The paired primordia later grow together. In most reptiles this fusion is incomplete and the tongue is forked.

The rudiments of the secondary hard palate appear in the form of horizontal bone folds of the upper jaw, which reach the middle and divide the oral cavity into the upper section - the respiratory (nasopharyngeal) and the lower - the secondary oral cavity. The lips are motionless.

Mammals- Mammalia,

Teeth heterodont, i.e. differentiated: they distinguish between incisors (incisivi), canines (canini), small molars (praemolares) and molars (molares). In pinnipeds and toothed whales, the teeth are not differentiated. The teeth sit in the alveoli; on the alveolar arches of the jaws, the base of the tooth narrows, forming a root.

The incisors and canines are very similar to the conical teeth of their ancestors (reptiles); the molars underwent the greatest evolutionary transformations and first appeared in beast-toothed lizards.

Due to the differentiation of teeth, the duration of functioning increases. In ontogenesis there are two changes of teeth ( diphyodontism): incisors, canines and large molars have two generations (deciduous and permanent); small radicals - only one.

The total number of teeth varies among different orders: for example, elephants have 6, wolves have 42, cats have 30, hares have 28, most primates and humans have 32.

The salivary glands of mammals are numerous: these are small ones - lingual, buccal, palatal, dental - homologous to the glands of reptiles, and large ones - sublingual, submandibular, parotid. Of these, the first two appeared as a result of differentiation of the sublingual gland of reptiles, and the parotid glands were a new acquisition of mammals. In the oral cavity - in higher mammals, large accumulations of lymphatic tissue - tonsils - appear.

Language, like that of reptiles, develops from three rudiments. The secondary hard palate becomes continuous, the oral cavity is completely separated from the nasal cavity, thereby achieving independence of the functions of the oral cavity and breathing. Posteriorly, the hard palate continues into the soft palate - a double fold of mucous membrane separating the oral cavity of the pharynx. The transverse ridges of the hard palate contribute to the grinding of food. In humans, they gradually disappear after birth.

The lips of marsupials and placentals are fleshy and mobile, which is associated with feeding the young with milk. The lips, cheeks and jaws define a space called the vestibule of the mouth.

In humans dental formula 2123

2123 (half of the upper and lower jaw).

The teeth, compared to other primates, have decreased in size, especially the canines; they do not protrude from the dentition and do not overlap. Diastemas (gaps between teeth) in the upper and lower jaws disappeared, the teeth became in a dense row, the dental arch acquired a rounded (parabolic) shape.

The molars have a four-cusped shape. The last pair of molars, “wisdom teeth,” erupt late - up to 25 years. They are clearly vestigial, reduced in size and often poorly differentiated.

During chewing, the lower jaw can perform rotational movements in relation to the upper jaw, due to the non-overlapping of the reduced canines and the complementary cusps of the chewing teeth of both jaws.

ATAVISTIC ANOMALIES OF THE HUMAN ORAL CAVITY:

a) a rare anomaly - homodont dental system, all teeth are conical;

b) tricuspid molars;

c) eruption of supernumerary teeth, i.e., a person can form more than 32 tooth germs;

d) absence of “wisdom teeth”;

e) a very rare malformation of the tongue - bifurcation of its end, as a result of non-fusion of paired rudiments in embryogenesis;

f) disruption of the fusion (this should occur by the end of the eighth week of embryogenesis) of the horizontal bony folds that form the hard palate, leading to non-fusion of the hard palate and the formation of a defect known as the “cleft palate”;

g) a cleft upper lip (“cleft lip”) occurs due to incomplete fusion of the dermal-mesodermal processes that form the upper lip, two of which (lateral) grow from the upper jaw, and one (central) from the frontonasal process.

SYNTHETIC THEORY OF EVOLUTION

The combination of Darwinism with ecology and genetics, which began in the 1920s, paved the way for the creation of a synthetic theory of evolution, which today is the only holistic, fairly fully developed theory of biological evolution that embodies classical Darwinism and population genetics.

The first scientist who introduced a genetic approach to the study of evolutionary processes was Sergei Sergeevich Chetverikov. In 1926, he published a scientific article “On some aspects of the evolutionary process from the point of view of modern genetics,” in which he was able to show, using the example of natural populations of Drosophila, that: 1) mutations constantly occur in natural populations; 2) recessive mutations are “absorbed like a sponge” by the species and in a heterozygous state can persist indefinitely; 3) as a species ages, more and more mutations accumulate in it and the characteristics of the species become loosened; 4) isolation and hereditary variability are the main factors of intraspecific differentiation; 5) panmixia leads to polymorphism of the species, and selection leads to monomorphism. In this work, S. S. Chetverikov emphasizes that the accumulation of small random mutations by selection leads to a natural, adaptively directed course of evolution. The work was continued by such domestic geneticists as Resovsky. , N. I. Vavilov and others. These works paved the way for the creation of the foundations of the synthetic theory of evolution.

In the 30s, the works of English scientists R. Fisher. J. Holdame. S. Wright laid the foundation for the synthesis of the theory of evolution and genetics in the West.

One of the first works that outlined the essence of the synthetic theory of evolution was the monograph “Genetics and the Origin of Species” (1937). The main attention in this work was paid to the study of the mechanisms of formation of the genetic structure of populations depending on the influence of such factors and causes of evolution as hereditary variability, natural selection, fluctuations in the number of individuals in populations (population waves), migration and, finally, reproductive isolation of new forms that have arisen within a species.

A domestic scientist made an outstanding contribution to the creation of a synthetic theory of evolution. Based on the creative combination of evolutionary theory, embryology, morphology, paleontology and genetics, he deeply explored the relationship between ontogenesis and phylogeny, studied the main directions of the evolutionary process, and developed a number of fundamental provisions of the modern theory of evolution. His main works: “The Organism as a Whole in Individual and Historical Development” (1938); "Paths and patterns of the evolutionary process" (1939); "Factors of Evolution" (1946).

An important place among the fundamental studies on the theory of evolution is occupied by the monograph “Evolution. Modern Synthesis” (1942), published in 1942 under the editorship of the prominent English evolutionist Julian Huxley, as well as studies of the rates and forms of evolution undertaken by George Simpson,

The synthetic theory of evolution is based on 11 main postulates, which are formulated in a concise form by a modern domestic geneticist, approximately in the following form:

1. The material for evolution is, as a rule, very small, discrete changes in heredity - mutations. Mutational variability as a source of material for selection is random. Hence the name of the concept proposed by its critic (1922), "tychogenesis" evolution based on chance.

2. The main or even the only driving factor of evolution is natural selection, based on the selection (selection) of random and small mutations. Hence the name of the theory - Selectogenesis.

3. The smallest evolving unit is a population, not an individual, as was assumed by Charles Darwin. Hence, special attention is paid to the study of populations as a structural unit of communities: species, herd, flock.

4. Evolution is gradual (gradational) and long-term. Speciation is thought of as the gradual replacement of one temporary population by a succession of subsequent temporary populations.

5. A species consists of many subordinate, at the same time morphologically, physiologically and genetically distinguishable, but not reproductively isolated, units - subspecies, populations (the concept of a broad polytypic species).

6. Evolution is divergent in nature (divergence of characters), that is, one taxon (systematic grouping) can become the ancestor of several daughter taxa, but each species has one single ancestral species, a single ancestral population.

7. Exchange of alleles (gene flow) is possible only within a species. Hence the species is a genetically closed and integral system.

8. Species criteria are not applicable to forms that reproduce asexually and parthenogenetically. These can be a huge variety of prokaryotes, lower eukaryotes without the sexual process, as well as some specialized forms of higher eukaryotes that have secondarily lost the sexual process (reproduce parthenogenetically)

9. Macroevolution (i.e., evolution above the species) follows the path of microevolution.

10. The actual taxon is of monophyletic origin (originating from one ancestral species); Monophylithic origin is the very right of the taxon to exist.

11. Evolution is unpredictable, that is, it has a character not directed towards the final goal.

In the late 50s and early 60s of the 20th century, additional information appeared indicating the need to revise some provisions of the synthetic theory. There is a growing need to correct some of its provisions.

Currently, the 1, 2 and 3 theses of the theory remain valid:

The 4th thesis is considered optional, since evolution can sometimes proceed very quickly in leaps and bounds. In 1982, a symposium was held in Dijon (France) on the rates and forms of speciation. It has been shown that in the case of polyploidy of chromosomal rearrangements, when reproductive isolation is formed almost immediately, speciation occurs spasmodically. However, in nature, there is no doubt that gradual speciation occurs through the selection of small mutations.

The 5th postulate is disputed, since many species are known with a limited range, within which it is not possible to divide them into independent subspecies, and relict species may generally consist of one population, and the fate of such species is, as a rule, short-lived.

The 7th thesis remains largely valid. However, there are known cases of genes leaking through the barriers of isolating mechanisms between individuals of different species. There is so-called horizontal gene transfer, for example, transduction - the transfer of bacterial genes from one type of bacteria to another through infection with bacteriophages. There are discussions around the issue of horizontal gene transfer. The number of publications on this issue is growing. The latest summary is presented in the monograph “Genome Variability” (1984).

Transposons, which, migrating within the genome, lead to a redistribution of the sequence of inclusion of certain genes, should also be considered from an evolutionary point of view.

The 8th thesis requires revision, since it is not clear where to include organisms that reproduce asexually, which, according to this criterion, cannot be classified as certain species.

The 9th thesis is currently being revised, since there is evidence that macroevolution can proceed both through microevolution and bypassing traditional microevolutionary paths.

The 10th thesis - the possibility of divergent origin of taxa from one ancestral population (or species) is now not denied by anyone. But evolution is not always divergent. In nature, the form of origin of new taxa through the merging of different, previously independent, i.e., reproductively isolated, branches is also common. The combination of different genomes and the creation of a new balanced genome occurs against the background of the action of natural selection, discarding non-viable combinations of genomes. In the 30s, a student carried out a resynthesis (reverse synthesis) of a cultivated plum, the origin of which was not clarified. created its copy by hybridizing sloe and cherry plum. Resynthesis has proven the hybridogenic origin of some other species of wild plants. Botanists consider hybridization to be one of the important ways of plant evolution.

The 11th thesis is also revised. This problem began to attract special attention in the early 20s of our century, when works on homologous series of hereditary variability appeared. He drew attention to the existence of a certain direction in the variability of organisms and suggested the possibility of predicting it based on an analysis of series of homologous variability in related forms of organisms.

In the 20s, the works of a domestic scientist appeared, who expressed the idea that evolution is to some extent predetermined, canalized in nature, that there are some forbidden paths of evolution, since the number of optimal solutions during this process is apparently limited (the theory of nomogenesis ).

Based on modern concepts, we can say that in evolution there is a certain vectorization of the ways of transforming characteristics, and we can to some extent predict the direction of evolution.

So, the modern theory of evolution has accumulated a huge arsenal of new facts and ideas, but there is no holistic theory that can replace the synthetic theory of evolution, and this is a matter for the future.

After the publication of Charles Darwin’s main work “The Origin of Species by Means of Natural Selection” (1859), modern biology moved far away not only from classical Darwinism of the second half of the 19th century, but also from a number of provisions of the synthetic theory of evolution. At the same time, there is no doubt that the main path of development of evolutionary biology lies in line with the directions laid down by Darwin.

GENETIC POLYMORPHISM

Genetic polymorphism is understood as a state of long-term diversity of genotypes, when the frequency of even the most rare genotypes in populations exceeds 1%. Genetic polymorphism is maintained through mutations and recombinations of genetic material. As numerous studies show, genetic polymorphism is widespread. Thus, according to theoretical calculations, the offspring from crossing two individuals that differ only in ten loci, each of which is represented by 4 possible alleles, will contain about 10 billion individuals with different genotypes.

The greater the stock of genetic polymorphism in a given population, the easier it is for it to adapt to a new environment and the faster evolution proceeds. However, it is almost impossible to estimate the number of polymorphic alleles using traditional genetic methods, since the very fact of the presence of a gene in a genotype is established by crossing individuals with different forms of the phenotype determined by this gene. Knowing what proportion of the population are individuals with different phenotypes, one can find out how many alleles are involved in the formation of a given trait.

Since the 60s of the 20th century, the method of protein electrophoresis (including enzymes) in gel has become widely used to determine genetic polymorphism. Using this method, it is possible to cause the movement of proteins in an electric field, depending on their size, configuration and total charge, to different parts of the gel, and then, based on the location and number of spots that appear, the substance under study can be identified. To assess the degree of polymorphism of certain proteins in populations, about 20 or more loci are usually studied, and then the number of allelic genes and the ratio of homo- and heterozygotes are determined mathematically. Research shows that some genes tend to be monomorphic, while others are extremely polymorphic.

There are transitional and balanced polymorphism, which depends on the selective value of genes and the pressure of natural selection.

Transitional polymorphism occurs in a population when an allele that was once common is replaced by other alleles that give their carriers higher fitness (multiple allelism). With transitional polymorphism, a directional shift is observed in the percentage of genotype forms. Transitional polymorphism is the main path of evolution, its dynamics. An example of transitional polymorphism can be the phenomenon of an industrial mechanism. Thus, as a result of air pollution in the industrial cities of England over the past hundred years, dark forms have appeared in more than 80 species of butterflies. For example, if before 1848 birch moths had a pale cream color with black dots and individual dark spots, then in 1848 the first dark-colored forms appeared in Manchester, and by 1895 98% of moths had already become dark-colored. This occurred as a result of sooting of tree trunks and selective eating of light-bodied moths by thrushes and robins. Later it was found that the dark body coloration of moths is caused by a mutant melanistic allele.

Balanced polymorphism x characterized by the absence of a shift in the numerical ratios of various forms and genotypes in populations located in stable environmental conditions. In this case, the percentage of forms either remains the same from generation to generation or fluctuates around some constant value. In contrast to transitional, balanced polymorphism is a static evolution. (1940) called it equilibrium heteromorphism.

An example of balanced polymorphism is the presence of two sexes in monogamous animals, since they have equal selective advantages. Their ratio in populations is 1:1. In polygamy, the selective value of representatives of different sexes may differ, and then representatives of one sex are either destroyed or are excluded from reproduction to a greater extent than individuals of the other sex. Another example is human blood groups according to the ABO system. Here, the frequency of different genotypes in different populations may vary, however, in each specific population it remains constant from generation to generation. This is explained by the fact that no one genotype has a selective advantage over others. So, although men with the first blood group, as statistics show, have a higher life expectancy than men with other blood groups, they are more likely than others to develop a duodenal ulcer, which, if perforated, can lead to death.

Genetic balance in populations can be disrupted by the pressure of spontaneous mutations that occur with a certain frequency in each generation. The persistence or elimination of these mutations depends on whether natural selection favors or opposes them. By tracing the fate of mutations in a particular population, we can talk about its adaptive value. The latter is equal to 1 if selection does not exclude it and does not prevent its spread. In most cases, the adaptive value of mutant genes is less than 1, and if the mutants are completely unable to reproduce, then it is zero. These kinds of mutations are rejected by natural selection. However, the same gene can mutate repeatedly, which compensates for its elimination caused by selection. In such cases, an equilibrium can be reached where the appearance and disappearance of mutated genes becomes balanced. An example is sickle cell anemia, when a dominant mutant gene in a homozygote leads to early death of the body, however, heterozygotes for this gene are resistant to malaria. In areas where malaria is common, there is a balanced polymorphism in the sickle cell anemia gene, since, along with the elimination of homozygotes, there is counter-selection in favor of heterozygotes. As a result of multi-vector selection, genotypes are maintained in the gene pool of populations in each generation, ensuring the fitness of organisms taking into account local conditions. In addition to the sickle cell gene, there are a number of other polymorphic genes in human populations that are thought to cause the phenomenon of heterosis

Recessive mutations (including harmful ones), which do not manifest themselves phenotypically in heterozygotes, can accumulate in populations to a higher level than harmful dominant mutations.

Genetic polymorphism is a prerequisite for continuous evolution. Thanks to it, in a changing environment there can always be genetic variants preadapted to these conditions. In a population of diploid dioecious organisms, a huge reserve of genetic variability can be stored in a heterozygous state without manifesting itself phenotypically. The level of the latter, obviously, can be even higher in polyploid organisms, in which not one, but several mutant alleles can be hidden behind a phenotypically manifested normal allele.

GENETIC LOAD

Genetic flexibility (or plasticity) of populations is achieved through the mutation process and combinative variability. And although evolution depends on the constant presence of genetic variation, one of its consequences is the appearance of poorly adapted individuals in populations, as a result of which the fitness of populations is always lower than that characteristic of optimally adapted organisms. This decrease in the average fitness of a population due to individuals whose fitness is below optimal is called genetic load. As the famous English geneticist J. Haldane wrote, characterizing the genetic load: “This is the price that a population is forced to pay for the right to evolve.” He was the first to draw the attention of researchers to the existence of genetic load, and the term “genetic load” itself was introduced in the 40s of the 20th century by G. Miller.

Genetic load in its broad sense is any reduction (actual or potential) in the fitness of a population due to genetic variability. Quantifying genetic load and determining its true impact on population fitness is a difficult task. According to the proposal (1965), individuals whose fitness is more than two standard deviations (-2a) below the average fitness of heterozygotes are considered carriers of genetic load.

It is customary to distinguish three types of genetic load: mutational, substitutional (transitional) and balanced. The total genetic load is made up of these three types of load. Mutation load - this is the proportion of the total genetic load that arises due to mutations. However, since most mutations are harmful, natural selection is directed against such alleles and their frequency is low. They are maintained in populations mainly due to newly emerging mutations and heterozygous carriers.

The genetic load that arises during dynamic changes in gene frequencies in a population in the process of replacing one allele with another is called substitutive (or transitional) cargo. Such substitution of alleles usually occurs in response to some change in environmental conditions, when previously unfavorable alleles become favorable, and vice versa (an example would be the phenomenon of the industrial mechanism of butterflies in ecologically unfavorable areas). In this case, the frequency of one allele decreases as the frequency of the other increases.

Balanced (stable) polymorphism occurs when many traits are maintained at relatively constant levels by balancing selection. At the same time, thanks to balanced selection acting in opposite directions, two or more alleys of any locus are preserved in populations, and, accordingly, different genotypes and phenotypes are preserved. An example is sickle cell. Here, selection is directed against the mutant allele, which is in a homozygous state, but at the same time acts in favor of heterozygotes, preserving it. The state of balanced load can be achieved in the following situations: 1) selection favors a given allele at one stage of ontogenesis and is directed against it at another; 2) selection favors the preservation of the allele in individuals of one sex and acts against it in individuals of the other sex; 3) within the same allele, different genotypes enable organisms to use different ecological niches, which reduces competition and, as a consequence, weakens elimination; 4) in subpopulations occupying different habitats, selection favors different alleles; 5) selection favors the preservation of the allele while it is rare and is directed against it when it occurs frequently.

Many attempts have been made to estimate the actual genetic load in human populations, but this has proven to be a very difficult task. It can be indirectly judged by the level of prenatal mortality and the birth of children with certain forms of developmental anomalies, especially from parents in inbred marriages, and even more so in incest.

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On some questions of evolution

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