The fish brain and its most important parts. Anisimova I.M., Lavrovsky V.V. Ichthyology. Structure and some physiological characteristics of fish. Nervous system and sensory organs

In nature there are many classes of different animals. One of them is fish. Many people don't even realize that these representatives of the animal kingdom have a brain. Read about its structure and features in the article.

Historical reference

Long ago, almost 70 million years ago, the World Ocean was inhabited by invertebrates. But fish, being the first to acquire a brain, destroyed a significant number of them. Since then they have dominated water space. Modern brain fish is very complex. Indeed, it is difficult to follow a behavior without a program. The brain solves this problem using different variants. Pisces preferred imprinting, when the brain is ready for the behavior that it sets at a certain point in its development.

For example, salmon have interesting feature: They swim to spawn in the river in which they themselves were born. At the same time they overcome huge distances, and they don’t have any map. This is possible thanks to this option behavior when certain parts of the brain are like a camera with a timer. The principle of operation of the device is this: there comes a moment when the diaphragm is triggered. Once in front of the camera, the images remain on film. So it is with fish. They are guided in their behavior precisely by images. Imprinting determines the individuality of fish. If given the same conditions, their different breeds will behave differently. Mammals have preserved the mechanism this method behavior, that is, imprinting, but the scope of its important forms has narrowed. In humans, for example, sexual skills have been preserved.

Parts of the brain in fish

This organ in this class is small in size. Yes, in a shark, for example, its volume is equal to thousandths of a percent of the total body weight, in sturgeon and bony fish it is hundredths, and in small fish it is about one percent. The fish brain has a peculiarity: the larger the individuals, the smaller it is.

The stickleback fish family, which lives in Lake Mivan in Iceland, has a brain whose size depends on the sex of the individuals: females have a smaller brain, males have a larger one.

The fish brain has five sections. These include:

• Forebrain, consisting of two hemispheres. Each of them controls the sense of smell and schooling behavior of fish.
• midbrain, from which the nerves that respond to stimuli arise, causing the eyes to move. This is the center of vision for fish. It regulates body balance and muscle tone.
• Cerebellum- organ responsible for movement.
• Medulla is the most important department. Performs many functions and is responsible for different reflexes.

The parts of the fish brain do not develop equally. This is influenced by the lifestyle of aquatic inhabitants and the condition environment. For example, pelagic species, having excellent movement skills in water, have a well-developed cerebellum, as well as vision. The structure of the fish brain is such that representatives of this class with a developed sense of smell are distinguished by an increased size of the forebrain; predators with good eyesight, - medium, sedentary representatives of the class - oblong.

Intermediate brain

It owes its formation to which are also called thalamus. Their location is the central part of the brain. The thalami have many formations in the form of nuclei, which transmit the received information to the fish’s brain. It arises different sensations associated with smell, vision, hearing.

The main thing is the integration and regulation of the body's sensitivity. It is also involved in the reaction that allows fish to move. If the thalamus is damaged, the level of sensitivity decreases, coordination is impaired, and vision and hearing also decrease.

Forebrain

It consists of a mantle, as well as striped bodies. The mantle is sometimes called a cloak. The location is the top and sides of the brain. The cloak has the appearance of thin epithelial plates. are located underneath it. The forebrain of fish is designed to perform functions such as:

• Olfactory. If this organ is removed from fish, they lose the conditioned reflexes developed to stimuli. Motor activity decreases, attraction to the opposite sex disappears.
• Protective and defensive. It manifests itself in the fact that representatives of the Pisces class maintain a gregarious lifestyle and take care of their offspring.

The brain is average

It consists of two departments. One of them is the visual roof, which is called the tectum. It is located horizontally. It looks like swollen optic lobes arranged in pairs. In fish with high organization, they are better developed than in cave and deep-sea representatives with poor vision. The other section is located vertically, it is called the tegmentum. It contains the highest visual center. What functions does it perform? midbrain?

• If you remove the visual roof from one eye, the other goes blind. The fish loses its sight when complete removal roof, in which the visual grasping reflex is located. Its essence lies in the fact that the head, body, and eyes of the fish move in the direction of food objects, which are imprinted on the retina.
• The fish's midbrain records coloration. When the upper roof is removed, the body of the fish becomes lighter, and if the eyes are removed, it darkens.
• It has connections with the forebrain and cerebellum. Coordinates the work of a number of systems: somatosensory, visual and olfactory.
• The middle part of the organ includes centers that regulate movement and maintain muscle tone.
• The fish brain makes reflex activity diverse. First of all, this affects reflexes associated with visual and auditory stimuli.

Brain oblongata

It takes part in the formation of the organ trunk. The medulla oblongata of fish is designed in such a way that substances, gray and white, are distributed without a clear boundary.

Performs following functions:

• Reflex. The centers of all reflexes are located in the brain, the activity of which ensures the regulation of breathing, the functioning of the heart and blood vessels, digestion, and the movement of fins. Thanks to this function, the activity of the taste organs is carried out.
• Conductor. It lies in the fact that the spinal cord and other parts of the brain conduct nerve impulses. The medulla oblongata is the site of the ascending tracts from the spinal cord to the brain, which go to the descending tracts connecting them.

Cerebellum

This formation, which has an unpaired structure, is located in the back part and partially covers the medulla oblongata. Consists of a middle part (body) and two ears (lateral sections).

Performs a number of functions:

• Coordinates movements and maintains normal muscle tone. If the cerebellum is removed, these functions are disrupted and the fish begin to swim in circles.
• Ensures the implementation of motor activity. When the body of the cerebellum is removed, the fish begins to swing in different directions. If you also remove the damper, movements are completely disrupted.
• The cerebellum regulates metabolism. This organ influences other parts of the brain through nucleoli located in the spinal cord and medulla oblongata.

Spinal cord

Its location is the neural arches (more precisely, their canals) of the fish spine, consisting of segments. The spinal cord in fish is a continuation of the medulla oblongata. From him to the right and left side Nerves extend between pairs of vertebrae. They carry irritating signals to the spinal cord. They innervate the surface of the body, trunk muscles and internal organs. What kind of brain do fish have? Head and back. The gray matter of the latter is located inside it, the white matter is outside.

127. Sketch a diagram external structure fish. Label its main parts.

128. List the structural features of fish associated with an aquatic lifestyle.
1) Streamlined torpedo-shaped body, flattened in the lateral or dorsal-abdominal (in benthic fish) directions. The skull is motionlessly connected to the spine, which has only two sections - the trunk and the caudal.
2) U bony fish There is a special hydrostatic organ - the swim bladder. As a result of changes in its volume, the buoyancy of the fish changes.
U cartilaginous fish buoyancy of the body is achieved by the accumulation of fat reserves in the liver, less often in other organs.
3) The skin is covered with placoid or bony scales, rich in glands that abundantly secrete mucus, which reduces friction of the body with water and performs a protective function.
4) Respiratory organs - gills.
5) Two-chamber heart (with venous blood), consisting of the atrium and ventricle; one circle of blood circulation. Organs and tissues are supplied arterial blood rich in oxygen. The life activity of fish depends on water temperature.
6) Body buds.
7) The sensory organs of fish are adapted to function in aquatic environment. The flat cornea and almost spherical lens allow fish to see only close objects. The sense of smell is well developed, allowing it to stay in a flock and detect food. The organ of hearing and balance is represented only by the inner ear. The lateral line organ allows one to navigate water currents, perceive the approach or distance of a predator, prey or school partner, and avoid collisions with underwater objects.
8) For the majority - external fertilization.

129. Fill out the table.

Fish organ systems.

130. Look at the drawing. Write the names of the sections of the fish skeleton indicated by numbers.

1) skull bones
2) spine
3) rays of the caudal fin
4) ribs
5) rays of the pectoral fin
6) gill cover

131. Color the organs in the drawing with colored pencils digestive system fish and write their names.

132. Draw and label the parts of the circulatory system of a fish. What is the significance of the circulatory system?

The circulatory system of fish ensures the movement of blood, which delivers oxygen and nutrients and removes metabolic products from them.

133. Study the table “Superclass Pisces. The structure of the perch." Look at the drawing. Write the names internal organs fish indicated by numbers.

1) kidney
2) swim bladder
3) bladder
4) ovary
5) intestines
6) stomach
7) liver
8) heart
9) gills.

134. Look at the drawing. Write the names of the parts of the fish's brain and parts of the nervous system indicated by numbers.

1) brain
2) spinal cord
3) nerve
4) forebrain
5) midbrain
6) cerebellum
7) medulla oblongata

135. Explain how the structure and location of the nervous system of fish differs from the nervous system of hydra and beetle.
Fish have a much more developed nervous system than hydra and beetle. There is a spinal and cephalic brain, consisting of sections. The spinal cord is located in the spine. Hydra has a diffuse nervous system, that is, it consists of scattered top layer cell bodies. The beetle has a ventral nerve cord, with an expanded ologopharyngeal ring and a suprapharyngeal ganglion at the head end of the body, but there is no brain as such.

136. Complete laboratory work “External structure of fish.”
1. Consider the features of the external structure of the fish. Describe the shape of its body, the color of its back and abdomen.
The fish has a streamlined oblong shape bodies. The color of the abdomen is silver, the back is darker.
2. Draw a drawing of the fish’s body and label its sections.
See question #127.
3. Examine the fins. How are they located? How many are there? Label the names of the fins in the picture.
The fish has paired fins: ventral, anal, pectoral and unpaired: caudal and dorsal.
4. Examine the fish's head. What sense organs are located on it?
On the head of the fish there are eyes, taste buds in oral cavity and on the surface of the skin, nostrils. There are 2 holes in the head section inner ear, on the border between the head and the body there are gill covers.
5. Examine the scales of the fish under a magnifying glass. Calculate the annual growth lines and determine the age of the fish.
The scales are bony, translucent, covered with mucus. The number of lines on the scales corresponds to the age of the fish.
6. Write down the features of the external structure of the fish associated with the aquatic lifestyle.
see question No. 128

Nervous system fish divided by peripheral And central. central nervous system consists of the brain and spinal cord, and peripheral- from nerve fibers and nerve cells.

Fish brain.

Fish brain consists of three main parts: forebrain, midbrain and hindbrain. Forebrain comprises telencephalon (telencephalon) and diencephalon - diencephalon. At the anterior end of the telencephalon are the bulbs responsible for the sense of smell. They receive signals from olfactory receptors.

Diagram of the olfactory chain in fish can be described as follows: In the olfactory lobes of the brain there are neurons that are part of an olfactory nerve or pair of nerves. Neurons join the olfactory areas of the telencephalon, which are also called the olfactory lobes. Olfactory bulbs are especially prominent in fish that use sensory organs, such as sharks, which rely on smell to survive.

The diencephalon consists of three parts: epithalamus, thalamus And hypothalamus and acts as a regulator internal environment fish body. The epithalamus contains the pineal organ, which in turn consists of neurons and photoreceptors. Pineal organ located at the end of the epiphysis and in many fish species it can be sensitive to light due to the transparency of the skull bones. Thanks to this, the pineal organ can act as a regulator of activity cycles and their changes.

In the midbrain of fish there are optic lobes And tegmentum or tire - both are used for processing optical signals. Optic nerve fish is very branched and has many fibers extending from the optic lobes. As with the olfactory lobes, enlarged optic lobes can be found in fish that depend on vision for their livelihoods.

The tegmentum in fish controls the internal muscles of the eye and thereby ensures its focusing on an object. The tegmentum can also act as a regulator of active control functions - this is where the locomotor region of the midbrain, responsible for rhythmic swimming movements, is located.

The hindbrain of fish consists of cerebellum, elongated brain And bridge. The cerebellum is unpaired organ, which performs the function of maintaining balance and controlling the position of the fish’s body in the environment. The medulla oblongata and the pons together make up brain stem, to which a large number of cranial nerves carrying sensory information extend. The majority of all nerves communicate with and enter the brain through the brainstem and hindbrain.

Spinal cord.

Spinal cord located inside the neural arches of the vertebrae of the fish spine. There is segmentation in the spine. In each segment, the neurons connect to the spinal cord via the dorsal roots, and the agility neurons exit them via the ventral roots. Within the central nervous system there are also interneurons that mediate communication between sensory neurons and sensory neurons.

Bony fishes are the largest class of vertebrates, numbering about 20,000 species. The most ancient representatives of this class descended from cartilaginous fish at the end of the Silurian. Currently, 99% of the class belong to the so-called bony fishes, which first appeared in the mid-Triassic, but their evolution for a long time progressed slowly and only at the end of the Cretaceous period it accelerated sharply and reached an amazing flowering in the Tertiary period. They inhabit a wide variety of bodies of water (rivers, seas and oceans down to the greatest depths; they are found in Arctic waters). Thus, bony fish are the vertebrates most adapted to living in an aquatic environment. In addition to bony fish, the class includes several dozen more species of ancient bony fish that have retained some of the features of cartilaginous fish.

general characteristics

Most species in this class are adapted for fast swimming, and their body shape is similar to that of sharks. Less fast-swimming fish have more tall body(for example, in many species of carp fish). Species that lead a sedentary lifestyle on the bottom (for example, flounder) have the same flattened body shape as stingrays.

Bony fish:

1 - herring (family Herring); 2 - salmon (family Salmonidae); 3 - carp (family Cyprinidae); 4- catfish (family Catfish); 5- pike (family Pike); 6- eel (family Acne);

7 - pike perch (family Perch); 8 - river goby (family Goby); 9 - flounder (Flounder family)

Veils. The body length of fish varies - from several centimeters to several meters. Unlike cartilaginous and ancient bony fishes, among bony fishes there are many small species who have mastered small biotopes that are inaccessible to larger species. The skin of the vast majority of bony fish is covered with small, bony, relatively thin scales that overlap each other in a tiled manner. They protect fish well from mechanical damage and provide sufficient body flexibility. There are cycloid scales with a rounded upper edge and ctenoid scales with small teeth on the upper edge. The number of scales in longitudinal and transverse rows for each species is more or less constant and is taken into account when determining the species of fish. In cold weather, the growth of fish and scales slows down or stops, so annual rings form on the scales, by counting which you can determine the age of the fish. In a number of species, the skin is bare and devoid of scales. There are many glands in the skin; the mucus they secrete reduces, like in other fish-like creatures, friction when swimming, protects against bacteria, etc. In the lower layers of the epidermis there are various pigment cells, thanks to which fish are hardly noticeable against the background of their environment. In some species, body color can change in accordance with changes in the color of the substrate. Such changes are carried out under the influence nerve impulses.

Nervous system. The size of the brain in relation to the size of the body is somewhat larger than that of cartilaginous fish. The forebrain is relatively small compared to other parts, but its striatum is large and, through their connections with other parts of the central nervous system, influences the implementation of some rather complex forms of behavior. There are no nerve cells in the roof of the forebrain. The diencephalon and the pineal and pituitary glands separated from it are well developed. The midbrain is larger than other parts of the brain; in its upper part there are two well-developed optic lobes. The cerebellum of well-swimming fish is large. The size and structure of the medulla oblongata and spinal cord have increased in size and complexity. The subordination of the latter to the brain, compared with what is observed in cartilaginous fish, has increased

Perch brain:

1 - olfactory capsule; 2 - olfactory lobes; 3 - forebrain; 4 - midbrain; 5 - cerebellum; 6 - medulla oblongata; 7 - spinal cord; 8 - orbital branch of the trigeminal nerve; 9 - auditory nerve; 10 - nervus vagus

Skeleton. During the evolution of the class under consideration, the skeleton gradually ossified. The notochord was preserved only among the lower representatives of the class, the number of which is insignificant. When studying the skeleton, you need to keep in mind that some bones arise from the replacement of cartilage bone tissue, others develop in the connective tissue layer of the skin. The former are called the main bones, the latter - the integumentary bones.

The brain section of the skull is a box that protects the brain and sense organs: smell, vision, balance and hearing.

Diagram of the arrangement of bones in the skull of a bony fish. The visceral skeleton is separated from brain skull. The operculum is not drawn. The main bones and cartilage are covered with dots, the integumentary bones are white:

/ - angular; 2 - articular; 3 - main occipital; 4 - main wedge-shaped; 5 - copula; 6 - dental; 7 - lateral olfactory; 8 - external pterygoid; 9 - internal pterygoid; 10 - lateral occipital; 11 - frontal; 12 - pendants; 13 - hyoid; 14 - ossified ligament; 15 - lateral wedge-shaped; 16 - middle olfactory; 17 - posterior pterygoid; 18- maxillary; 19 - nasal; 20 - oculocuneiform; 21 - parietal; 22 - palatal; 23 - premaxillary; 24 - parasphenoid; 25 - square; 26 - upper occipital; 27 - additional; 28 - opener; 29-33 - ear bones; I-V - gill arches

The roof of the skull is formed by paired nasal, frontal, and parietal bones. The latter are adjacent to the superior occipital bone, which, together with the paired lateral occipital bones and the main occipital bone, forms back skulls The bottom of the skull consists (from front to back) of the vomer, the parasphenoid (a wide, long bone very characteristic of a fish skull), and the sphenoid bone. The front part of the skull is occupied by a capsule protecting the olfactory organs; On the sides there are bones surrounding the eyes and a row of bones protecting the organs of hearing and balance.

The visceral part of the skull consists of a number of bony gill arches, which support and protect the gill apparatus and the anterior part of the digestive system. Each of the mentioned arches includes several bones. The arches to which the gills are attached are found on each side in most fish. Below, the gill arches are connected to each other, and the anterior one is connected to the hyoid arch, which consists of several bones. The upper of these bones, the hyoid-maxillary (hyomandibular), is attached to the medulla of the skull in the area auditory department and is connected through the quadrate bone to the bones surrounding the oral cavity. Thus, the hyoid arch serves to connect the branchial arches with the rest of the visceral region, and its upper bone with the medulla of the skull.

The edges of the mouth and the entire oral cavity are reinforced by a number of bones. The maxillary row of bones is represented (on each side) by the premaxillary and maxillary bones. Next comes a series of bones: the palatine, several pterygoids and the quadrate. The quadrate bone is adjacent to the suspension (hyomandibular) at the top, and to the lower jaw at the bottom. The latter consists of several bones: the dental (the largest), the angular and the articular, connecting to the quadrate. In ancient fish (which still had a cartilaginous skeleton), all arches of the visceral part of the skull bore gills, and later the anterior ones of these arches turned into hyoid arches and jaw rows of bones.

Spinal column consists of a large number of biconcave (amphicoelous) vertebrae, in the spaces between which remains of the notochord are preserved. A long spinous process extends upward and somewhat backward from each vertebra. The bases of these processes are separated, and they form a canal through which the spinal cord passes. From bottom side The vertebral bodies have two short transverse processes, to which long curved ribs are attached in the trunk region. They end freely in the muscles and form the frame of the side walls of the body. In the caudal part of the body, only the lower spinous processes extend downward from the vertebrae.

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The brain of fish is very small, amounting to thousandths of a percent of the body weight in sharks, and hundredths of a percent in bony fish and sturgeons. In small fish, the brain mass reaches about 1%.

The fish brain consists of 5 sections: the forebrain, intermediate, middle, cerebellum and medulla oblongata. The development of individual parts of the brain depends on the lifestyle of fish and their ecology. Thus, good swimmers (mostly pelagic fish) have a well-developed cerebellum and optic lobes. In fish with a well-developed sense of smell, the forebrain is enlarged. Fish with well-developed vision (predators) have a midbrain. Sedentary fish have a well-developed medulla oblongata.

The medulla oblongata is a continuation of the spinal cord. It, together with the midbrain and diencephalon, forms the brainstem. In the medulla oblongata, compared to the spinal cord, there is no clear distribution of gray and white matter. The medulla oblongata performs the following functions: conductive and reflex.

The conductor function is to conduct nerve impulses between the spinal cord and other parts of the brain. Through the medulla oblongata there are ascending tracts from the spinal cord to the brain and descending tracts connecting the brain with the spinal cord.

Reflex function medulla oblongata. The medulla oblongata contains centers for both relatively simple and complex reflexes. Due to the activity of the medulla oblongata, the following reflex reactions are carried out:

1) regulation of breathing;

2) regulation of cardiac activity and blood vessels;

3) regulation of digestion;

4) regulation of the functioning of the taste organs;

5) regulation of chromatophores;

6) regulation of the operation of electrical organs;

7) regulation of fin movement centers;

8) regulation of the spinal cord.

The medulla oblongata contains the nuclei of six pairs of cranial nerves (V‑X).

V pair – trigeminal nerve is divided into 3 branches: the ophthalmic nerve innervates the anterior part of the head, the maxillary nerve innervates the skin of the anterior part of the head and palate, and the mandibular nerve innervates the oral mucosa and mandibular muscles.

VI pair - the auricular nerve innervates the muscles of the eyes.

VII pair - the facial nerve is divided into 2 lines: the first innervates the lateral line of the head, the second - the mucous membrane of the palate, sublingual area, taste buds of the oral cavity and muscles of the operculum.

VIII pair - auditory or sensory nerve - innervates inner ear and a labyrinth.

Pair IX - glossopharyngeal nerve - innervates the mucous membrane of the palate and the muscles of the first branchial arch.

X pair - the vagus nerve is divided into two branching branches: the lateral nerve innervates the lateral line organs in the trunk, the nerve of the operculum innervates the gill apparatus and other internal organs.

The midbrain of fish is represented by two sections: the visual roof (tectum) - located horizontally and the tegmentum - located vertically.

The tectum or visual roof of the midbrain is swollen in the form of paired optic lobes, which are well developed in fish with a high degree of development of the visual organs and poorly in blind deep-sea and cave fish. On inside The tectum contains the longitudinal torus. It is associated with vision. The higher visual center of fish is located in the tegmentum of the midbrain. The fibers of the second pair of optic nerves end in the tectum.

The midbrain performs the following functions:

1) Function visual analyzer as evidenced by the following experiments. After removing the textum from one side of the fish's eyes, the one lying on the opposite side becomes blind. When the entire tectum is removed, total blindness. The tectum also contains the center of the visual grasp reflex, which consists in the fact that the movements of the eyes, head and torso are directed so as to maximize the fixation of the food object in the area of ​​greatest visual acuity, i.e. in the center of the retina. The tectum contains the centers of the III and IV pairs of nerves that innervate the muscles of the eyes, as well as the muscles that change the width of the pupil, i.e. performing accommodation, which allows you to clearly see objects at different distances due to the movement of the lens.

2) Participates in the regulation of fish coloration. So, after removing the tectum, the body of the fish becomes lighter, while when the eyes are removed, the opposite phenomenon is observed - darkening of the body.

3) In addition, the tectum is closely connected with the cerebellum, hypothalamus, and through them with the forebrain. Therefore, the tectum coordinates the functions of the somatosensory (balance, posture), olfactory and visual systems.

4) The tectum is connected with the VIII pair of nerves, which perform acoustic and receptor functions, and with the V pair of nerves, i.e. trigeminal nerves.

5) Afferent fibers from the lateral line organs, from the auditory and trigeminal nerves approach the midbrain.

6) The tectum contains afferent fibers from the olfactory and taste receptors.

7) In the midbrain of fish there are centers for regulating movement and muscle tone.

8) The midbrain has an inhibitory effect on the centers of the medulla oblongata and spinal cord.

Thus, the midbrain regulates a number of vegetative functions body. Due to the midbrain, the reflex activity of the body becomes diverse (orienting reflexes to sound and visual stimuli appear).

Diencephalon. The main structure of the diencephalon is the visual thalamus. Under the visual thalamus is the subtubercular region - the epithalamus, and under the thalamus is the subtubercular region - the hypothalamus. The diencephalon in fish is partially covered by the roof of the midbrain.

The epithalamus consists of the pineal gland, a rudiment of the parietal eye, which functions as endocrine gland. The second element of the epithalamus is the frenulum (habenula), which is located between the forebrain and the roof of the midbrain. The frenulum is the connecting link between the pineal gland and the olfactory fibers of the forebrain, i.e. participates in the functions of light reception and smell. The epithalamus is connected to the midbrain through efferent nerves.

The thalamus (visual thalamus) in fish is located in the central part of the diencephalon. In the visual thalamus, especially in the dorsal part, many nuclear formations were found. The nuclei receive information from receptors, process it and transmit it to certain areas of the brain, where corresponding sensations arise (visual, auditory, olfactory, etc.). Thus, the thalamus is an organ of integration and regulation of the body’s sensitivity, and also takes part in the implementation of motor reactions of the body.

When the visual tuberosities are damaged, there is a decrease in sensitivity, hearing, and vision, which causes a loss of coordination.

The hypothalamus consists of an unpaired hollow protrusion - a funnel, which forms a vascular sac. The vascular sac responds to changes in pressure and is well developed in deep-sea pelagic fish. The vascular sac is involved in the regulation of buoyancy, and through its connection with the cerebellum, it participates in the regulation of balance and muscle tone.

The hypothalamus is the main center where information from the forebrain arrives. Afferent fibers from taste endings and from speaker system. Efferent nerves from the hypothalamus go to the forebrain, to the dorsal thalamus, tectum, cerebellum and neurohypophysis, i.e. regulates their activities and influences their work.

The cerebellum is an unpaired formation, it is located in the back of the brain and partially covers the medulla oblongata. The body of the cerebellum is distinguished ( middle part) and cerebellar ears (i.e. two lateral sections). The anterior end of the cerebellum forms the valve.

In leading fish sedentary image life (for example, in bottom fish, such as scorpionfish, gobies, anglerfish), the cerebellum is underdeveloped in comparison with fish leading active image life (pelagic, such as mackerel, herring or predators - pike perch, tuna, pike).

Functions of the cerebellum. When the cerebellum is completely removed from active fish, a decrease in muscle tone (atony) and impaired coordination of movements are observed. This was expressed in the circular swimming of the fish. In addition, the fish’s reaction to painful stimuli weakens, sensory disturbances occur, and tactile sensitivity disappears. After approximately three to four weeks, the lost functions are restored due to the regulatory processes of other parts of the brain.

After removal of the cerebellar body in bony fishes, movement disorders in the form of body swaying from side to side. After removal of the body and valve of the cerebellum, motor activity is completely disrupted, and trophic disorders develop. This indicates that the cerebellum also regulates metabolism in the brain.

It should be noted that the cerebellar ears reach large sizes in fish that have a well-developed lateral line. Thus, the cerebellum is the place of closure of conditioned reflexes coming from the lateral line organs.

Thus, the main functions of the cerebellum are coordination of movement, normal distribution of muscle tone and regulation of autonomic functions. The cerebellum exerts its influence through the nuclear formations of the midbrain and medulla oblongata, as well as motor neurons spinal cord.

The forebrain of fish consists of two parts: the mantle or cloak and the striatum. The mantle, or the so-called cloak, lies dorsally, i.e. from above and from the sides in the form of a thin epithelial plate above the striatum. In the anterior wall of the forebrain there are olfactory lobes, which are often differentiated into the main part, stalk and olfactory bulb. The mantle receives secondary olfactory fibers from the olfactory bulb.

Functions of the forebrain. The forebrain of fish performs the olfactory function. This is evidenced, in particular, by the following experiments. When the forebrain is removed, fish experience a loss of developed conditioned reflexes to olfactory stimuli. In addition, removal of the forebrain of fish leads to a decrease in their motor activity and to a decrease in pack conditioned reflexes. The forebrain also plays an important role in the sexual behavior of fish (when it is removed, sexual desire disappears).

Thus, the forebrain is involved in the defensive reaction, the ability to swim in schools, the ability to care for offspring, etc. It has a general stimulating effect on other parts of the brain.

7. Principles of reflex theory I.P. Pavlova

Pavlov's theory is based on the basic principles of conditioned reflex activity of the brain of animals, including fish:

1. The principle of structure.

2. The principle of determinism.

3. Principle of analysis and synthesis.

The principle of structure is as follows: each morphological structure corresponds to a specific function. The principle of determinism is that reflex reactions have strict causality, i.e. they are deterministic. For the manifestation of any reflex, a reason, a push, an influence from the external world or the internal environment of the body is necessary. Analytical and synthetic activity of the central nervous system is carried out due to the complex relationships between the processes of excitation and inhibition.

According to Pavlov's theory, the activity of the central nervous system is based on a reflex. A reflex is a causally determined (deterministic) reaction of the body to changes in the external or internal environment, carried out with the obligatory participation of the central nervous system in response to irritation of receptors. This is how the emergence, change or cessation of any activity of the body occurs.

Pavlov divided all reflex reactions of the body into two main groups: unconditioned reflexes and conditioned reflexes. Unconditioned reflexes are innate, inherited reflex reactions. Unconditioned reflexes appear in the presence of a stimulus without special, special conditions (swallowing, breathing, salivation). Unconditioned reflexes have ready-made reflex arcs. Unconditioned reflexes are divided into various groups according to a number of signs. Based on biological characteristics, they are divided into food (search, intake and processing of food), defensive (defensive reaction), sexual (animal behavior), orientation (orientation in space), postural (adopting a characteristic pose), locomotor (motor reactions).

Depending on the location of the irritated receptor, exteroceptive reflexes are distinguished, i.e. reflexes that arise when the outer surface of the body (skin, mucous membranes) is irritated, interoreceptive reflexes, i.e. reflexes that occur when internal organs are irritated, proprioceptive reflexes that occur when receptors are irritated skeletal muscles, joints, ligaments.

Depending on the part of the brain that is involved in the reflex reaction, the following reflexes are distinguished: spinal (spinal cord) - the centers of the spinal cord are involved, bulbar - the centers of the medulla oblongata, mesencephalic - the centers of the midbrain, diencephalic - the centers of the diencephalon.

In addition, reactions are divided according to the organ that is involved in the response: motor or locomotor (muscle is involved), secretory (endocrine or exocrine gland is involved), vasomotor (vessel is involved), etc.

Unconditioned reflexes are specific reactions. They are characteristic of all representatives of this species. Unconditioned reflexes are relatively constant reflex reactions, stereotypical, unchangeable, inert. As a result, it is impossible to adapt to changing living conditions only through unconditioned reflexes.

Conditioned reflexes are a temporary nervous connection of the body with any stimulus from the external or internal environment of the body. Conditioned reflexes are acquired during the individual life of an organism. They are not the same among different representatives of a given species. Conditioned reflexes do not have ready-made reflex arcs, they are formed under certain conditions. Conditioned reflexes are changeable, easily arise and also easily disappear, depending on the conditions in which the given organism is located. Conditioned reflexes are formed on the basis of unconditioned reflexes under certain conditions.

For the formation of a conditioned reflex, it is necessary to combine two stimuli in time: indifferent (indifferent) for a given type of activity, which will later become a conditioned signal (knocking on glass) and an unconditioned stimulus that causes a certain unconditioned reflex (food). The conditioned signal always precedes the action of the unconditioned stimulus. Reinforcement of the conditioned signal with an unconditioned stimulus must be repeated. It is necessary that the conditioned and unconditioned stimuli meet the following requirements: the unconditioned stimulus must be biologically strong (food), the conditioned stimulus must have moderate optimal strength (knock).

8. Fish behavior

The behavior of fish becomes more complex during their development, i.e. ontogeny. The simplest reaction of the fish body in response to a stimulus is kinesis. Kinesis is an increase in motor activity in response to adverse effects. Kinesis is already observed at late stages embryonic development of fish, when there is a decrease in oxygen content in the environment. Increased movement of larvae in the egg or in the water in this case helps improve gas exchange. Kinesis promotes the movement of larvae from bad conditions habitats in the best. Another example of kinesis is the random movement of schooling fish (top fish, uklya, etc.) when a predator appears. This confuses him and prevents him from focusing on one fish. This can be considered a defensive reaction of schooling fish.

More complex shape The behavior of fish is taxis - this is the directed movement of fish in response to a stimulus. There are positive taxis (attraction) and negative taxis (avoidance). An example is phototaxis, i.e. fish reaction to the light factor. Thus, anchovy and big-eyed sprat have positive phototaxis, i.e. are well attracted to light, forming clusters, which makes it possible to use this property in fishing for these fish. In contrast to the Caspian sprat, the mullet exhibits negative phototaxis. Representatives of this species of fish strive to get out of the illuminated background. This property is also used by humans when fishing for this fish.

An example of negative phototaxis can be the behavior of salmon larvae. During the day they hide among stones and gravel, which allows them to avoid predators. And the larvae of carp fish exhibit positive phototaxis, which allows them to avoid stifling deep-sea areas and find more food.

Taxi directions may be subject to change age-related changes. Thus, salmon fry at the pied stage are typical bottom-dwelling sedentary fish, protecting their territory from their own kind. They avoid light, live among stones, easily change color to match the color of their environment, and can hide when frightened. As they grow before moving into the sea, they change color to a non-silver color, gather in flocks, and lose aggressiveness. When frightened, they quickly swim away, are not afraid of light, and, on the contrary, stay near the surface of the water. As you can see, the behavior of juveniles of this species changes to the opposite with age.

Fish, unlike higher vertebrates, lack a cerebral cortex, which is of key importance in the development of conditioned reflexes. However, fish are capable of producing them without it, for example, a conditioned reflex to sound (Frolov’s experiment). After the action of the sound stimulus, the current was turned on a few seconds later, to which the fish reacted with body movement. After a certain number of repetitions, the fish, without waiting for the action of the electric current, responded to the sound, i.e. reacted with body movement. In this case, the conditioned stimulus is sound, and the unconditioned stimulus is the induction current.

Unlike higher animals, fish have less developed reflexes and are unstable and difficult to develop. Fish are less capable of differentiation than higher animals, i.e. distinguish between conditioned stimuli or changes in the external environment. It should be noted that in bony fish conditioned reflexes are developed faster and they are more persistent than in others.

There are works in the literature that show fairly persistent conditioned reflexes, where the unconditioned stimuli are a triangle, a circle, a square, various letters, etc. If you place a feeder in a reservoir that gives a portion of food in response to pressing a lever, tugging a bead or other devices, then the fish master this device quickly enough and receive food.

Those who are involved in aquarium fish farming have observed that when approaching the aquarium, fish gather at the feeding area in anticipation of food. This is also a conditioned reflex, and in this case you are the conditioned stimulus; knocking on the glass of an aquarium can also serve as a conditioned stimulus.

In fish hatcheries, fish are usually fed at certain times of the day, so they often gather in certain areas at feeding time. Fish also quickly get used to the type of food, the method of distributing food, etc.

Big practical significance may have the development of conditioned reflexes to a predator in the conditions of fish hatcheries and NVH in juvenile commercial fish, which are then released into natural reservoirs. This is due to the fact that in the conditions of fish hatcheries and fisheries, juveniles have no experience of communicating with enemies and in the early stages become prey for predators until they receive an individual and spectacular experience.

Using conditioned reflexes explore various aspects of biology various fish, such as the spectral sensitivity of the eye, the ability to distinguish silhouettes, the effect of various toxicants, the hearing of fish by the strength and frequencies of sound, the thresholds of taste sensitivity, the role of various parts of the nervous system.

In the natural environment, the behavior of fish depends on their lifestyle. Schooling fish have the ability to coordinate maneuvers when feeding, when they see a predator, etc. Thus, the appearance of a predator or food organisms at one edge of the flock causes the entire flock to react accordingly, including individuals who did not see the stimulus. The reaction can be very varied. So, at the sight of a predator, the flock instantly scatters. You can observe this in the spring in the coastal zone of our reservoirs; the fry of many fish are concentrated in schools. This is one of the types of imitation. Another example of imitation is following the leader, i.e. for an individual whose behavior lacks elements of oscillation. Leaders are most often individuals who have extensive individual experience. Sometimes even a fish of another species can serve as such a leader. Thus, carp quickly learn to take food on the fly if trout or carp individuals who know how to do this are placed next to them.

When fish live in groups, a “social” organization with dominant and subordinate fish may arise. Thus, in a flock of Mozambian tilapia, the main one is the most intensely colored male, the next ones in the hierarchy are lighter. Males, no different in color from females, are subordinate and do not participate in spawning at all.

The sexual behavior of fish is very diverse, including elements of courtship and competition, nest building, etc. Complex spawning and parental behavior is characteristic of fish with low individual fecundity. Some fish take care of eggs, larvae and even fry (guard the nest, aerate the water (pike perch, smelt, catfish)). The juveniles of some fish species feed near their parents (for example, discus even feed the juveniles with their mucus). The young of some fish species hide in their parents' mouth and gill cavities (tilapia). Thus, the plasticity of fish behavior is very diverse, as can be seen from the above materials.

Questions for self-control:

1. Features of the structure and function of nerves and synapses.

2. Parabiosis as a special type of localized excitation.

3. Scheme of the structure of the nervous system of fish.

4. Structure and functions of the peripheral nervous system.

5. Features of the structure and function of parts of the brain.

6. Principles and essence of reflex theory.

7. Peculiarities of fish behavior.