The central nervous system and its functions. Central nervous system. About the structure of the central nervous system

The central nervous system (CNS) consists of the brain and spinal cord and their protective membranes. The membranes of the brain and spinal cord are structured as follows. On the outside is the dura mater, under it is the arachnoid mater, and then is the pia mater, fused with the surface of the brain. Between the pia mater and the arachnoid membrane is the subarachnoid space, which contains cerebrospinal fluid, in which both the brain and spinal cord literally float. The meninges and cerebrospinal fluid play a protective role, as well as the role of shock absorbers, softening all kinds of shocks and shocks that the body experiences that could lead to damage to the nervous system.

The central nervous system is made up of gray and white matter. Gray matter consists mainly of cell bodies, as well as some processes of nerve cells. Thanks to the presence of gray matter, our brain “thinks” by forming chains between the bodies of nerve cells. White matter consists of long processes of nerve cells - axons, which act as conductors and transmit impulses from one center to another.

The pathways of the nervous system are usually organized in such a way that information (for example, pain or tactile - the feeling of touch) from the right side of the body enters the left side of the brain and vice versa. This rule also applies to the descending motor pathways: the right half of the brain mainly controls the movements of the left half of the body, and the left half controls the right.

The brain consists of three main structures: the cerebral hemispheres, the cerebellum and the brainstem. The cerebral hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intelligence, personality, speech, and understanding. In each of the cerebral hemispheres, the following formations are distinguished: underlying isolated accumulations (nuclei) of gray matter, which contain many important centers - the so-called subcortical formations; a large mass of white matter located above them; covering the outside of the hemispheres is a thick layer of gray matter with numerous convolutions that makes up the cerebral cortex.

The cerebellum also consists of gray and white matter. The cerebellum primarily provides coordination of movements.

The brainstem is formed by a mass of gray and white matter that is not divided into layers. The brain stem contains such important centers as the respiratory and vasomotor centers, as well as the nuclei of the cranial nerves, which regulate the functioning of the organs and muscles of the head and neck.

The spinal cord, located inside the spinal column and protected by its bone tissue, has a cylindrical shape and is covered with three membranes.

Peripheral nervous system

The peripheral system (PNS) provides two-way communication between the central parts of the nervous system and the organs and systems of the body. The PNS is represented by cranial and spinal nerves. These nerves emerge at different levels from the brain stem and spinal cord to reach the muscles and organs. The peripheral nervous system also includes the enteric nervous system, located in the intestinal wall.

Autonomic nervous system

The autonomic or autonomic nervous system (ANS) regulates the activity of involuntary muscles, the heart muscle, and various glands. Its structures are located in both the central and peripheral nervous systems - these are the nuclei and plexuses located in the brain and spinal cord, as well as the nerves that go from these nuclei and plexuses to the internal organs. The activity of the autonomic nervous system is aimed at maintaining homeostasis, that is, a relatively stable state of the internal environment of the body. This system ensures constant body temperature, optimal blood pressure; it is also “responsible” for the frequency of heartbeat and breathing.

Solving problems associated with diseases of the nervous system is quite difficult. In any case, first of all, a union between the doctor and the patient is necessary, the patient’s understanding of the reasons for the development of the disease, a serious attitude towards fighting the disease and achieving the goal of recovery.

There are no processes in the human body that are not related to the state of the nervous system, not caused by its excessive tension or insufficient activity. And only maintaining the normal activity of this complexly organized system, even in cases where one or another damage has already occurred, gives a chance to defeat the disease. To direct the work of the nervous system, and therefore the body as a whole, in the right direction is the doctor’s task; to enable the healing processes to actively develop is not an easy job for the patient.

First of all, an integrated approach to solving problems is needed:

Timely holding of consultations and collegial adoption of correct decisions in complex clinical cases;

A combination of drug and non-drug treatment methods. In this case, rationally organized diagnostic and treatment processes make it possible to achieve the first positive results in a short time.

A special role in the treatment of patients with neurological diseases is played by rehabilitation and readaptation, which are of great importance in the world today.

Using rehabilitation programs specially developed for each patient, taking into account his individual characteristics, rehabilitation doctors will teach you to walk, do everything possible to restore the movements of the limbs and fingers, teach you to speak and even sing, and help you gain self-confidence. At the same time, it is very important to remember that the sooner program rehabilitation is started after an injury or stroke, the greater the guarantee of success, the better the result.

A common problem is headaches. Modern brain research systems greatly speed up the process of identifying the causes of headaches, allowing, first of all, to exclude high intracranial pressure, chronic inflammation or a tumor.

But much more often, headaches are associated with excessive tension in the muscles of the head and neck and are called “tension headaches.” In this case, drug treatments have a temporary effect, since they not only do not eliminate the causes of pain, but also do not affect the multiple mechanisms that underlie chronic headaches. And although the mechanisms of headaches (vascular, neuralgic, muscular, etc.) must be clarified in each case, many years of experience show that the greatest effect in the treatment of chronic headaches is exerted by the so-called reflex methods of influencing all of the above mechanisms.

Relaxation massage methods, complex effects on the muscular system, foot massage, acupuncture - a reliable arsenal of modern therapy methods that provide a lasting treatment effect. Maintenance preventive courses of treatment are guaranteed to avoid exacerbations.

Tension of muscle fibers very often causes pain in those muscles that are located close to the spine. In this case, it is enough to properly organize the impact of the hands on various muscle groups, a combination of relaxing and tonic methods, a complex of physical therapy, which allows you to avoid the use of strong painkillers and other medications, the overall effect of which is not indifferent to the body.

Another category of patients who now often turn to a neurologist are children. And here we also need an integrated approach, a team of experienced specialists: neurologists, massage therapists, speech therapists, psychologists who, working according to a unified treatment and rehabilitation program, will be able to do everything possible to develop and correct movements and speech, develop logical thinking and memory, maintain stable emotional condition and good mood of each child. And every child requires special attention.

An emotionally gentle diagnosis of a child’s condition, developed today by psychologists, eliminates communication difficulties, manifestations of negativism and increased anxiety in children, and solves the problem of psychological comfort of the child and his parents. Much attention today is paid to the use of various types of massage in the treatment of children: classical, segmental, acupressure, “Thai” and others. The enormous reserve capabilities of the child’s body with a complex impact on the child’s physical and mental development systems make it possible to obtain significant treatment results in a short time.

The intense rhythm of life, an abundance of information, a busy work schedule, when there is absolutely no time for rest and it seems that you are working to the limit of your capabilities - all this often leads to emotional breakdowns, depression, and even a feeling of physical ill health. This is how healthy people develop chronic fatigue syndrome.

It is best to break this vicious circle in time. For this purpose, it is necessary, first of all, to use preventive treatment programs that will relieve tension, accumulated fatigue, and restore vigor and good mood. Consultations with a psychologist will help you understand the problems and find the right solutions that are important for normalizing the atmosphere at home and in the team of employees.

A sense organ is a specialized peripheral anatomical and physiological system that has developed in the process of evolution, which, thanks to its receptors, ensures the receipt and primary analysis of information from the surrounding world and from other organs of the body itself, that is, from the external and internal environment of the body. Some senses can complement others to a certain extent.

A person receives information through five senses:

Eyes (vision);

Ears, including the vestibular system (hearing and balance);

Tongue (taste);

Nose (sense of smell);

Skin (touch).

Information about stimuli affecting the receptors of the human senses is transmitted to the central nervous system. She analyzes incoming information and identifies it (sensations arise). Then a response signal is generated, which is transmitted along the nerves to the corresponding organs of the body.

The sense organs (organa sensuum) are receptors, or peripheral parts of the analyzers, that perceive various types of stimuli coming from the external environment. Each receptor is capable of perceiving certain factors, reacting to so-called adequate stimuli. Then the irritation is transformed into a nerve impulse and enters through the conductive pathways into the intermediate sections of the analyzers, formed by nerve centers located in the spinal cord and in the brain stem. From here the impulse is transmitted to the central part of the analyzers - to the cerebral cortex. It is here that the analysis and synthesis of nervous excitation occurs as a result of the reception of the stimulus by the senses. All three groups of departments (peripheral, intermediate and central) are interconnected morphologically and functionally, representing a single system.

The organ of vision (organum visus) perceives light stimuli. With their help, the process of perception of surrounding objects is carried out: size, shape, color, distance to them, movement, etc. 90% of information from the surrounding world comes through the eye.

The organ of hearing - the ear - is a complex vestibular-auditory organ that performs two functions: it perceives sound impulses and is responsible for the position of the body in space and the ability to maintain balance. This is a paired organ that is located in the temporal bones of the skull, limited externally by the auricles. The human ear perceives sound waves with a length of approximately 20 m to 1.6 cm, which corresponds to 16 - 20,000 Hz (oscillations per second).

The organ of smell (organum olfactus) is a peripheral part of the olfactory analyzer and perceives chemical irritations when steam or gas enters the nasal cavity. The olfactory epithelium (epithelium olfactorium) is located in the upper part of the nasal passage and the postero-superior part of the nasal septum, in the mucous membrane of the nasal cavity. This section is called the olfactory region of the nasal mucosa (regio olfactoria tunicae mucosae nasi). It contains the olfactory glands (glandulae olfactoriae). The receptors of the olfactory region of the nasal mucosa are capable of perceiving several thousand different odors.

The organ of taste (organum custus) is a peripheral section of the taste analyzer and is located in the oral cavity. The tongue is an unpaired outgrowth of the floor of the oral cavity in vertebrates and humans.

The main function is to help with chewing food. Important functions of the tongue are also determining the taste of food through taste buds (papillae) located on its upper surface, and changing the acoustic properties of the oral cavity when making guttural sounds. The latter function is especially pronounced in people who have a developed speech system.

Touch (kinesthetics, tactile sense) is one of the five main types of senses that a person is capable of, which consists in the ability to feel touch, perceive something with receptors located in the skin, muscles, and mucous membranes. The sensations caused by touch, pressure, vibration, texture and extension have a different nature. Caused by the work of two types of skin receptors: nerve endings surrounding the hair follicles and capsules consisting of connective tissue cells

The vestibular apparatus (lat. vestibulum - vestibule), an organ that perceives changes in the position of the head and body in space and the direction of body movement in vertebrates and humans; part of the inner ear.

The vestibular apparatus is a complex receptor of the vestibular analyzer. The structural basis of the vestibular apparatus is a complex of accumulations of ciliated cells of the inner ear, endolymph, calcareous formations included in it - otoliths and jelly-like cupules in the ampoules of the semicircular canals. Two types of signals come from balance receptors: static (related to body position) and dynamic (related to acceleration). Both signals arise from mechanical stimulation of sensitive hairs by displacement of either otoliths (or cupules) or endolymph. Typically, the otolith is denser than the surrounding endolymph and is supported by sensory hairs.

When the position of the body changes, the direction of the force acting from the otolith on the sensitive hairs changes.

Due to the different inertia of the endolymph and cupula, upon acceleration, the cupula shifts, and the friction resistance in the thin channels serves as a damper (silencer) of the entire system. The oval sac (utriculus) plays a leading role in the perception of body position and is probably involved in the sensation of rotation. The round sac (sacculus) complements the oval one and is apparently necessary for the perception of vibrations.

The human body works as a whole. The coherence and interaction of all organs is ensured by the central nervous system. It is found in all living beings and consists of nerve cells and their processes.

The central nervous system in vertebrates is represented by the brain and spinal cord, in invertebrates - by a system of unified nerve ganglia. The central nervous system is protected by the bone formations of the skeleton: the skull and spine.

Structure of the central nervous system

Anatomy of the central nervous system studies the structure of the brain and spinal cord, which are connected to each organ through the peripheral nervous system.

The central nervous system is responsible for feelings such as:

• hearing;
• vision;
• touch;
• emotions;
• memory;
• thinking.

The brain structure of the central nervous system mainly contains white and gray substances.

Gray are nerve cells with small processes. Located in the spinal cord, it occupies the central part, encircling the spinal canal. As for the brain of the head, in this organ the gray matter makes up its cortex and has separate formations in the white matter. The white substance is located under the sulfur. Its structure contains nerve fibers that form nerve bundles. A number of these “ligaments” make up a nerve.

The brain and spinal cord are surrounded by three membranes:

1. Solid. This is the outer shell. It is located in the internal cavity of the skull and spinal canal.
2. Arachnoid. This cover is located under the hard part. In its structure it has nerves and blood vessels.
3. Vascular. This membrane is directly connected to the brain. She goes into his furrows. Formed from many blood arteries. The arachnoid is separated from the choroid by a cavity that is filled with medulla.

Spinal cord as part of the central nervous system

This component of the central nervous system is located in the spinal canal. It stretches from the back of the head to the lumbar region. The brain has longitudinal grooves on both sides, and the spinal canal in the center. On the outer side of the brain of the back there is a white substance.

The gray element mainly consists of the lateral, posterior and anterior horny areas. The anterior horns contain motor nerve cells, the posterior ones have intercalary ones that produce contact between sensory (lying in the nodal sections) and motor cells. Attached to the anterior horny areas of the motor particles are processes that make up the fibers. Those neurons that create the dorsal roots join the posterior horny zones.

These roots are intermediaries between and the brain of the back. The excitation coming to the brain enters the interneuron, and then through the axon it goes to the desired organ. Reaching the opening between the vertebrae, the sensory cells connect with their motor counterparts. After this, they are divided into posterior and anterior branches, which also consist of motor and sensory fibers. 62 mixed nerves extend from each vertebra in two directions.

Human head brain

This organ is located in the brain section of the skull. Conventionally, it has five sections; inside it there are four cavities that are filled with cerebrospinal fluid. The majority of the organ consists of the hemispheres (80%). The second largest share is occupied by the trunk.

It has the following structural sections:

• average;
• cerebral;
• oblong;
• intermediate.

Brain regions

1. Medulla. This area continues the spinal cord and has a structure similar to it. Its structure is formed of white matter with areas of gray substance from which the nerves of the skull extend. The upper section ends with the pons, and the lower peduncles are connected to the sides from the cerebellum. Almost this entire brain is covered by the hemispheres. In the gray element of this part of the brain there are centers responsible for the functioning of the lungs, heart function, swallowing, coughing, tears, salivation and the formation of gastric juice. Any damage to this area can stop breathing and heart activity, that is, lead to death.
2. Hindbrain. This part includes the cerebellum and the pons. The Varoliev bridge is a section starting from the oblong and ending at the top with “legs”. Its lateral parts form the middle cerebellar peduncles. The pons includes the facial, trigeminal, abducens and auditory nerves. The cerebellum is located behind the pons and medulla oblongata. This part of the organ consists of a gray component, which is the cortex, and a white substance with gray areas. The cerebellum consists of two hemispheres, the middle section and three pairs of peduncles. It is through these legs, which consist of nerve fibers, that it is connected to other areas of the brain. Thanks to the cerebellum, a person can coordinate his movements, maintain balance, keep his muscles toned, and perform clear and smooth movements. Through the pathways of the central nervous system, the cerebellum transmits impulses to muscle tissue. But its work is controlled by the cerebral cortex.
3. Midbrain. Anatomically located in front of the pons. Consists of four colliculi and cerebral peduncles. In the center is a canal connecting the third and fourth ventricles. This duct is framed by a gray element. The cerebral peduncles contain pathways that connect the medulla oblongata and pons with the hemispheres. Thanks to the midbrain, it is possible to maintain tone and implement reflexes. It allows you to perform activities such as standing and walking. In addition, sensory nuclei are located in the quadrigeminal tubercles, which are connected with vision and hearing. They carry out light and sound reflexes.
4. Intermediate. It is located in front of the brain “legs”. The divisions of this part of the central nervous system are a pair of visual tuberosities, geniculate bodies, supracubertal and subtubercular regions. The structure of the diencephalon includes white matter and accumulations of gray substance. The main centers of sensitivity are located here - the visual hillocks. This is where impulses from all over the body enter and are then sent to the cerebral cortex. Under the tuberosity is the hypothalamus, where the autonomic system is represented by the subcortical higher center. Thanks to it, metabolism and heat transfer occur. This center maintains the stability of the internal environment. The auditory and optic nerves are located in the geniculate bodies.
5. Forebrain. Its structure is the cerebral hemispheres with a connecting middle part. These hemispheres are separated by a “passage”, at the bottom of which is the corpus callosum. It connects both parts with nerve cell processes. The top of the hemispheres is the cerebral cortex, consisting of neurons and processes. Underneath it is located white matter, which functions as pathways. It unites the centers of the hemisphere into one whole. This substance consists of nerve cells that form the subcortical nuclei of the gray element. The cerebral cortex has a rather complex structure. It consists of more than 14 billion nerve particles arranged in six balls. They have different shapes, sizes and connections.

The cerebral cortex of the head has convolutions and grooves.

Those, in turn, divide the surface into four sections:

• occipital;
• frontal;
• parietal;
• temple.

The central and temporal sulci are among the deepest. The first passes through the hemispheres, the second separates the temporal region of the brain from the others. In the area of ​​the frontal lobe, in front of the central sulcus, is the central anterior gyrus. The posterior central gyrus is located behind the main sulcus.

The base of the brain is made up of the lower zone of the hemispheres and the brainstem. Each part of the cerebral cortex corresponds to its own part of the body. The centers of almost all sensitive systems are located in this segment. Analysis of incoming information takes place in the cerebral cortex. The main areas of the cortex are: olfactory, motor, sensitive, auditory, visual.

The structure of the central nervous system differs between higher and lower living organisms. The system of lower animals has a network type structure, higher organisms (including humans) have a neurogenic type of NS structure. In the first case, impulses can be transmitted diffusely; in the second case, each cell functions as a separate unit, although it is connected to other neurons. The afferent nervous system transmits impulses from all organs to the central nervous system.

The points of connection of these particles are called synapses. The area between the cell and its process is filled with glia. This is a collection of special particles that, unlike neurons, are capable of dividing. The most common type of such particles are astrocytes. They clean the extracellular space from excess ions and mediators, eliminating chemical problems that interfere with coordinated reactions on the surface of nerve cells. In addition, astrocytes provide glucose to active cells and change the direction of oxygen transfer.

Many nervous processes occur in the parts of the central nervous system. Simple and complex highly differentiated reflective reactions are carried out thanks to this system. The functions of the central nervous system can be characterized by two purposes: communication and interaction of a living organism and the external environment and regulation of organ function. This is one of the necessary conditions for the normal functioning of the body.

In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a single whole. The coordination of the functions of internal organs is ensured by the nervous system. In addition, the nervous system communicates between the external environment and the regulatory organ, responding to external stimuli with appropriate reactions.

The perception of changes occurring in the external and internal environment occurs through nerve endings - receptors.

Any stimulation (mechanical, light, sound, chemical, electrical, temperature) perceived by the receptor is converted (transformed) into the process of excitation. Excitation is transmitted along sensitive - centripetal nerve fibers to the central nervous system, where an urgent process of processing nerve impulses occurs. From here, impulses are sent along the fibers of centrifugal neurons (motor) to the executive organs that implement the response - the corresponding adaptive act.

This is how a reflex occurs (from the Latin “reflexus” - reflection) - a natural reaction of the body to changes in the external or internal environment, carried out through the central nervous system in response to irritation of receptors.

Reflex reactions are varied: constriction of the pupil in bright light, salivation when food enters the oral cavity, etc.

The path along which nerve impulses (excitation) pass from the receptors to the executive organ during the implementation of any reflex is called reflex arc.

The reflex arcs are closed in the segmental apparatus of the spinal cord and brain stem, but they can also be closed higher, for example, in the subcortical ganglia or in the cortex.

Taking into account the above, there are:

• central nervous system (brain and spinal cord) and
• the peripheral nervous system, represented by nerves extending from the brain and spinal cord and other elements lying outside the spinal cord and brain.

The peripheral nervous system is divided into somatic (animal) and autonomic (or autonomic).

• The somatic nervous system primarily communicates the body with the external environment: perception of irritations, regulation of movements of the striated muscles of the skeleton, etc.
• vegetative - regulates metabolism and the functioning of internal organs: heartbeat, peristaltic contractions of the intestines, secretion of various glands, etc.

The autonomic nervous system, in turn, based on the segmental principle of structure, is divided into two levels:

• segmental - includes the sympathetic, anatomically connected to the spinal cord, and the parasympathetic, formed by clusters of nerve cells in the midbrain and medulla oblongata, nervous systems
• suprasegmental level - includes the reticular formation of the brain stem, hypothalamus, thalamus, amygdala and hippocampus - limbic-reticular complex

The somatic and autonomic nervous systems function in close cooperation, but the autonomic nervous system has some independence (autonomy), controlling many involuntary functions.

CENTRAL NERVOUS SYSTEM

Represented by the brain and spinal cord. The brain consists of gray and white matter.

Gray matter is a collection of neurons and their short processes. In the spinal cord it is located in the center, surrounding the spinal canal. In the brain, on the contrary, gray matter is located along its surface, forming a cortex (cloak) and separate clusters, called nuclei, concentrated in the white matter.

The white matter is located under the gray matter and is composed of nerve fibers covered with membranes. Nerve fibers, when connected, form nerve bundles, and several such bundles form individual nerves.

The nerves through which excitation is transmitted from the central nervous system to the organs are called centrifugal, and the nerves that conduct excitation from the periphery to the central nervous system are called centripetal.

The brain and spinal cord are surrounded by three membranes: dura mater, arachnoid membrane and vascular membrane.

• Hard - external, connective tissue, lining the internal cavity of the skull and spinal canal.
• The arachnoid is located under the dura mater - it is a thin shell with a small number of nerves and vessels.
• The choroid is fused with the brain, extends into the grooves and contains many blood vessels.

Between the choroid and arachnoid membranes, cavities filled with brain fluid are formed.

Spinal cord is located in the spinal canal and has the appearance of a white cord stretching from the occipital foramen to the lower back. There are longitudinal grooves along the anterior and posterior surfaces of the spinal cord; the spinal canal runs in the center, around which the gray matter is concentrated - an accumulation of a huge number of nerve cells that form a butterfly outline. Along the outer surface of the spinal cord there is white matter - a cluster of bundles of long processes of nerve cells.

In the gray matter, anterior, posterior and lateral horns are distinguished. The anterior horns contain motor neurons, and the posterior horns contain intercalary neurons, which communicate between sensory and motor neurons. Sensory neurons lie outside the cord, in the spinal ganglia along the course of the sensory nerves.

Long processes extend from the motor neurons of the anterior horns - the anterior roots, which form motor nerve fibers. The axons of sensory neurons approach the dorsal horns, forming the dorsal roots, which enter the spinal cord and transmit excitation from the periphery to the spinal cord. Here the excitation is switched to the interneuron, and from it to the short processes of the motor neuron, from which it is then communicated to the working organ along the axon.

In the intervertebral foramina, the motor and sensory roots unite, forming mixed nerves, which then split into anterior and posterior branches. Each of them consists of sensory and motor nerve fibers. Thus, at the level of each vertebra, a total of 31 pairs of mixed-type spinal nerves extend from the spinal cord in both directions.

The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments with each other and the spinal cord with the brain. Some pathways are called ascending or sensory, transmitting excitation to the brain, others are called descending or motor, which conduct impulses from the brain to certain segments of the spinal cord.

Function of the spinal cord. The spinal cord performs two functions:

1. reflex [show] .

   Each reflex is carried out by a strictly defined part of the central nervous system - the nerve center. A nerve center is a collection of nerve cells located in one of the parts of the brain and regulating the activity of an organ or system. For example, the center of the knee reflex is located in the lumbar spinal cord, the center of urination is in the sacral, and the center of pupil dilation is in the upper thoracic segment of the spinal cord. The vital motor center of the diaphragm is localized in the III-IV cervical segments. Other centers - respiratory, vasomotor - are located in the medulla oblongata.

   The nerve center consists of many interneurons. It processes the information that comes from the corresponding receptors, and generates impulses that are transmitted to the executive organs - the heart, blood vessels, skeletal muscles, glands, etc. As a result, their functional state changes. To regulate the reflex and its accuracy, the participation of the higher parts of the central nervous system, including the cerebral cortex, is necessary.

   The nerve centers of the spinal cord are directly connected to the receptors and executive organs of the body. Motor neurons of the spinal cord provide contraction of the muscles of the trunk and limbs, as well as the respiratory muscles - the diaphragm and intercostal muscles. In addition to the motor centers of skeletal muscles, the spinal cord contains a number of autonomic centers.

2. conductor [show] .

Bundles of nerve fibers that form white matter connect various parts of the spinal cord to each other and the brain to the spinal cord. There are ascending pathways that carry impulses to the brain, and descending pathways that carry impulses from the brain to the spinal cord. According to the first, excitation arising in the receptors of the skin, muscles, and internal organs is carried along the spinal nerves to the dorsal roots of the spinal cord, perceived by sensitive neurons of the spinal nodes and from here sent either to the dorsal horns of the spinal cord, or as part of the white matter reaches the trunk, and then the cerebral cortex.

Descending pathways carry excitation from the brain to the motor neurons of the spinal cord. From here, excitation is transmitted along the spinal nerves to the executive organs. The activity of the spinal cord is controlled by the brain, which regulates spinal reflexes.

Brain located in the brain part of the skull. Its average weight is 1300 - 1400 g. After a person is born, brain growth continues up to 20 years. It consists of five sections: the forebrain (cerebral hemispheres), diencephalon, midbrain, hindbrain and medulla oblongata. Inside the brain there are four interconnected cavities - the cerebral ventricles. They are filled with cerebrospinal fluid. The first and second ventricles are located in the cerebral hemispheres, the third - in the diencephalon, and the fourth - in the medulla oblongata.

The hemispheres (the newest part in evolutionary terms) reach a high level of development in humans, making up 80% of the mass of the brain. The phylogenetically more ancient part is the brain stem. The trunk includes the medulla oblongata, pons, midbrain and diencephalon.

The white matter of the trunk contains numerous nuclei of gray matter. The nuclei of 12 pairs of cranial nerves also lie in the brain stem. The brainstem is covered by the cerebral hemispheres.

Medulla- continuation of the dorsal one and repeats its structure: grooves also lie here on the front and back surfaces. It consists of white matter (conducting bundles), where clusters of gray matter are scattered - the nuclei from which cranial nerves originate - from the IX to the XII pairs, including the glossopharyngeal (IX pair), vagus (X pair), innervating the organs respiration, blood circulation, digestion and other systems, sublingual (XII pair). At the top, the medulla oblongata continues into a thickening - the pons, and the lower cerebellar peduncles extend from the sides of it. From above and from the sides, almost the entire medulla oblongata is covered by the cerebral hemispheres and the cerebellum.

The gray matter of the medulla oblongata contains vital centers that regulate cardiac activity, breathing, swallowing, carrying out protective reflexes (sneezing, coughing, vomiting, lacrimation), secretion of saliva, gastric and pancreatic juice, etc. Damage to the medulla oblongata can cause death due to cessation of cardiac activity and respiration.

hindbrain includes the pons and cerebellum. The pons is bounded below by the medulla oblongata, passes into the cerebral peduncles above, and its lateral sections form the middle cerebellar peduncles. The substance of the pons contains the nuclei of the V to VIII pairs of cranial nerves (trigeminal, abducens, facial, auditory).

The cerebellum is located posterior to the pons and medulla oblongata. Its surface consists of gray matter (cortex). Under the cerebellar cortex there is white matter, in which there are accumulations of gray matter - the nuclei. The entire cerebellum is represented by two hemispheres, the middle part - the vermis and three pairs of legs formed by nerve fibers, through which it is connected to other parts of the brain. The main function of the cerebellum is unconditional reflex coordination of movements, determining their clarity, smoothness and maintaining body balance, as well as maintaining muscle tone. Through the spinal cord, along the pathways, impulses from the cerebellum enter the muscles. The cerebral cortex controls the activity of the cerebellum.

Midbrain located in front of the pons, it is represented by the quadrigeminal and cerebral peduncles. In its center there is a narrow canal (brain aqueduct) that connects the third and fourth ventricles. The cerebral aqueduct is surrounded by gray matter, in which the nuclei of the III and IV pairs of cranial nerves lie. The cerebral peduncles continue the pathways from the medulla oblongata and the pons to the cerebral hemispheres. The midbrain plays an important role in the regulation of tone and in the implementation of reflexes that make standing and walking possible. The sensitive nuclei of the midbrain are located in the quadrigeminal tubercles: the upper ones contain nuclei associated with the organs of vision, and the lower ones contain nuclei associated with the organs of hearing. With their participation, orienting reflexes to light and sound are carried out.

Diencephalon occupies the highest position in the trunk and lies anterior to the cerebral legs. Consists of two visual tuberosities, supracubertal, subtubercular region and geniculate bodies. Along the periphery of the diencephalon there is white matter, and in its thickness there are nuclei of gray matter. The visual hillocks are the main subcortical centers of sensitivity: impulses from all the receptors of the body arrive here along the ascending pathways, and from here to the cerebral cortex. In the subcutaneous part (hypothalamus) there are centers, the totality of which represents the highest subcortical center of the autonomic nervous system, regulating metabolism in the body, heat transfer, and the constancy of the internal environment. The parasympathetic centers are located in the anterior parts of the hypothalamus, and the sympathetic centers in the posterior parts. The subcortical visual and auditory centers are concentrated in the nuclei of the geniculate bodies.

The second pair of cranial nerves, the optic ones, goes to the geniculate bodies. The brain stem is connected to the environment and to the organs of the body by cranial nerves. By their nature they can be sensitive (I, II, VIII pairs), motor (III, IV, VI, XI, XII pairs) and mixed (V, VII, IX, X pairs).

Forebrain consists of highly developed hemispheres and the middle part connecting them. The right and left hemispheres are separated from each other by a deep fissure, at the bottom of which lies the corpus callosum. The corpus callosum connects both hemispheres through long processes of neurons that form pathways.

The cavities of the hemispheres are represented by the lateral ventricles (I and II). The surface of the hemispheres is formed by gray matter or the cerebral cortex, represented by neurons and their processes; under the cortex lies white matter - pathways. Pathways connect individual centers within one hemisphere, or the right and left halves of the brain and spinal cord, or different floors of the central nervous system. The white matter also contains clusters of nerve cells that form the subcortical nuclei of the gray matter. Part of the cerebral hemispheres is the olfactory brain with a pair of olfactory nerves extending from it (I pair).

The total surface of the cerebral cortex is 2000-2500 cm 2, its thickness is 1.5-4 mm. Despite its small thickness, the cerebral cortex has a very complex structure.

The cortex includes more than 14 billion nerve cells, arranged in six layers, which differ in shape, neuron size and connections. The microscopic structure of the cortex was first studied by V. A. Bets. He discovered pyramidal neurons, which were later given his name (Betz cells).

In a three-month embryo, the surface of the hemispheres is smooth, but the cortex grows faster than the braincase, so the cortex forms folds - convolutions limited by grooves; they contain about 70% of the surface of the cortex. The grooves divide the surface of the hemispheres into lobes.

Each hemisphere has four lobes:

• frontal
• parietal
• temporal
• occipital

The deepest grooves are the central one, which runs across both hemispheres, and the temporal one, separating the temporal lobe of the brain from the rest; The parieto-occipital sulcus separates the parietal lobe from the occipital lobe.

In front of the central sulcus (Rolandic sulcus) in the frontal lobe is the anterior central gyrus, behind it is the posterior central gyrus. The lower surface of the hemispheres and the brain stem is called the base of the brain.

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, the visual center is located in the cortex of the occipital lobe of the hemispheres, and the auditory center is located in the upper part of the temporal lobe. 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 corresponding sensitive zones of the cerebral cortex, where analysis is carried out and a specific sensation is formed - visual, olfactory, etc., and it can control their work.

The functional system, consisting of a receptor, a sensitive pathway and a zone of the cortex where this type of sensitivity is projected, I. P. Pavlov called an analyzer.

Analysis and synthesis of the received information is carried out in a strictly defined area - the zone of the cerebral cortex. The most important areas of the cortex are motor, sensitive, visual, auditory, and olfactory. The motor zone is located in the anterior central gyrus in front of the central sulcus of the frontal lobe, the zone of musculocutaneous sensitivity is behind the central sulcus, in the posterior central gyrus of the parietal lobe. The visual zone is concentrated in the occipital lobe, the auditory zone is in the superior temporal gyrus of the temporal lobe, and the olfactory and gustatory zones are in the anterior temporal lobe.

Many neural processes take place in the cerebral cortex. Their purpose is twofold: interaction of the body with the external environment (behavioral reactions) and the unification of body functions, nervous regulation of all organs. The activity of the cerebral cortex of humans and higher animals was defined by I. P. Pavlov as higher nervous activity, which is a conditioned reflex function of the cerebral cortex.

PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system is formed by nerves emerging from the central nervous system and ganglia and plexuses located mainly near the brain and spinal cord, as well as near various internal organs or in the walls of these organs. The peripheral nervous system is divided into somatic and autonomic divisions.

Somatic nervous system

This system is formed by sensory nerve fibers going to the central nervous system from various receptors and motor nerve fibers innervating skeletal muscles. The characteristic features of the fibers of the somatic nervous system are that they are not interrupted anywhere along the entire length from the central nervous system to the receptor or skeletal muscle, have a relatively large diameter and a high speed of excitation. These fibers make up most of the nerves that exit the central nervous system and form the peripheral nervous system.

There are 12 pairs of cranial nerves leaving the brain. The characteristics of these nerves are given in Table 1. [show] .

Table 1. Cranial nerves

Each segment of the spinal cord gives off one pair of nerves containing sensory and motor fibers. All sensory, or centripetal, fibers enter the spinal cord through the dorsal roots, on which there are thickenings - nerve ganglia. These nodes contain the bodies of centripetal neurons.

Fibers of motor, or centrifugal, neurons exit the spinal cord through the anterior roots. Each segment of the spinal cord corresponds to a specific part of the body - a metamer. However, the innervation of metameres occurs in such a way that each pair of spinal nerves innervates three adjacent metameres, and each metamer is innervated by three adjacent segments of the spinal cord. Therefore, in order to completely denervate any metamer of the body, it is necessary to cut the nerves of three adjacent segments of the spinal cord.

The autonomic nervous system is a section of the peripheral nervous system that innervates internal organs: heart, stomach, intestines, kidneys, liver, etc. It does not have its own special sensitive pathways. Sensitive impulses from organs are transmitted along sensory fibers, which also pass as part of the peripheral nerves; they are common to the somatic and autonomic nervous systems, but make up a smaller part of them.

Unlike the somatic nervous system, autonomic nerve fibers are thinner and conduct excitation much more slowly. On the way from the central nervous system to the innervated organ, they are necessarily interrupted with the formation of a synapse.

Thus, the centrifugal pathway in the autonomic nervous system includes two neurons - preganglionic and postganglionic. The body of the first neuron is located in the central nervous system, and the body of the second is outside it, in the nerve nodes (ganglia). There are many more postganglionic neurons than preganglionic neurons. As a result of this, each preganglionic fiber in the ganglion approaches and transmits its excitation to many (10 or more) postganglionic neurons. This phenomenon is called animation.

According to a number of signs, the autonomic nervous system is divided into sympathetic and parasympathetic divisions.

Sympathetic department The autonomic nervous system is formed by two sympathetic chains of nerve nodes (paired border trunk - vertebral ganglia), located on either side of the spine, and nerve branches that extend from these nodes and go to all organs and tissues as part of mixed nerves. The nuclei of the sympathetic nervous system are located in the lateral horns of the spinal cord, from the 1st thoracic to the 3rd lumbar segments.

Impulses entering the organs through sympathetic fibers provide reflex regulation of their activity. In addition to internal organs, sympathetic fibers innervate blood vessels in them, as well as in the skin and skeletal muscles. They strengthen and increase heart rate, cause rapid redistribution of blood by narrowing some vessels and dilating others.

Parasympathetic Division It is represented by a number of nerves, among which the largest is the vagus nerve. It innervates almost all organs of the thoracic and abdominal cavity.

The nuclei of the parasympathetic nerves lie in the middle, medulla oblongata and sacral parts of the spinal cord. Unlike the sympathetic nervous system, all parasympathetic nerves reach peripheral nerve nodes located in the internal organs or on the approaches to them. The impulses conducted by these nerves cause a weakening and slowing of cardiac activity, a narrowing of the coronary vessels of the heart and brain vessels, dilation of the vessels of the salivary and other digestive glands, which stimulates the secretion of these glands, and increases the contraction of the muscles of the stomach and intestines.

The main differences between the sympathetic and parasympathetic divisions of the autonomic nervous system are given in table. 2. [show] .

Table 2. Autonomic nervous system

Most internal organs receive dual autonomic innervation, that is, they are approached by both sympathetic and parasympathetic nerve fibers, which function in close interaction, exerting the opposite effect on the organs. This is of great importance in adapting the body to constantly changing environmental conditions.

L. A. Orbeli made a significant contribution to the study of the autonomic nervous system [show] .

Orbeli Leon Abgarovich (1882-1958) - Soviet physiologist, student of I. P. Pavlov. Academician Academy of Sciences of the USSR, Academy of Sciences of the Armenian SSR and Academy of Medical Sciences of the USSR. Head of the Military Medical Academy, Institute of Physiology named after. I, P. Pavlova of the USSR Academy of Sciences, Institute of Evolutionary Physiology, vice-president of the USSR Academy of Sciences.

The main direction of research is the physiology of the autonomic nervous system.

L. A. Orbeli created and developed the doctrine of the adaptive-trophic function of the sympathetic nervous system. He also conducted research on the coordination of the activity of the spinal cord, the physiology of the cerebellum, and higher nervous activity.

SOCIAL-TECHNOLOGICAL INSTITUTE OF MOSCOW STATE SERVICE UNIVERSITY

ANATOMY OF THE CENTRAL NERVOUS SYSTEM

(Tutorial)

O.O. Yakimenko

Moscow - 2002

A manual on the anatomy of the nervous system is intended for students of the Socio-Technological Institute, Faculty of Psychology. The content includes basic issues related to the morphological organization of the nervous system. In addition to anatomical data on the structure of the nervous system, the work includes histological cytological characteristics of nervous tissue. As well as questions of information about the growth and development of the nervous system from embryonic to late postnatal ontogenesis.

For clarity of the presented material, illustrations are included in the text. For independent work of students, a list of educational and scientific literature, as well as anatomical atlases, is provided.

Classic scientific data on the anatomy of the nervous system are the foundation for the study of the neurophysiology of the brain. Knowledge of the morphological characteristics of the nervous system at each stage of ontogenesis is necessary to understand the age-related dynamics of human behavior and psyche.

SECTION I. CYTOLOGICAL AND HISTOLOGICAL CHARACTERISTICS OF THE NERVOUS SYSTEM

General plan of the structure of the nervous system

The main function of the nervous system is to quickly and accurately transmit information, ensuring the interaction of the body with the outside world. Receptors respond to any signals from the external and internal environment, converting them into streams of nerve impulses that enter the central nervous system. Based on the analysis of the flow of nerve impulses, the brain forms an adequate response.

Together with the endocrine glands, the nervous system regulates the functioning of all organs. This regulation is carried out due to the fact that the spinal cord and brain are connected by nerves to all organs, bilateral connections. Signals about their functional state are received from organs to the central nervous system, and the nervous system, in turn, sends signals to the organs, correcting their functions and ensuring all vital processes - movement, nutrition, excretion and others. In addition, the nervous system ensures coordination of the activities of cells, tissues, organs and organ systems, while the body functions as a single whole.

The nervous system is the material basis of mental processes: attention, memory, speech, thinking, etc., with the help of which a person not only cognizes the environment, but can also actively change it.

Thus, the nervous system is that part of a living system that specializes in transmitting information and integrating reactions in response to environmental influences.

Central and peripheral nervous system

The nervous system is divided topographically into the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which consists of nerves and ganglia.

Nervous system

According to the functional classification, the nervous system is divided into somatic (divisions of the nervous system that regulate the work of skeletal muscles) and autonomic (vegetative), which regulates the work of internal organs. The autonomic nervous system has two divisions: sympathetic and parasympathetic.

Nervous system

somatic autonomic

sympathetic parasympathetic

Both the somatic and autonomic nervous systems include central and peripheral divisions.

Nervous tissue

The main tissue from which the nervous system is formed is nervous tissue. It differs from other types of tissue in that it lacks intercellular substance.

Nervous tissue consists of two types of cells: neurons and glial cells. Neurons play a major role in providing all functions of the central nervous system. Glial cells have an auxiliary role, performing supporting, protective, trophic functions, etc. On average, the number of glial cells exceeds the number of neurons in a ratio of 10:1, respectively.

The meninges are formed by connective tissue, and the brain cavities are formed by a special type of epithelial tissue (epindymal lining).

Neuron is a structural and functional unit of the nervous system

A neuron has characteristics common to all cells: it has a plasma membrane, a nucleus and cytoplasm. The membrane is a three-layer structure containing lipid and protein components. In addition, on the surface of the cell there is a thin layer called glycocalis. The plasma membrane regulates the exchange of substances between the cell and the environment. For a nerve cell, this is especially important, since the membrane regulates the movement of substances that are directly related to nerve signaling. The membrane also serves as the site of electrical activity that underlies rapid neural signaling and the site of action of peptides and hormones. Finally, its sections form synapses - the place of contact between cells.

Each nerve cell has a nucleus that contains genetic material in the form of chromosomes. The nucleus performs two important functions - it controls the differentiation of the cell into its final form, determining the types of connections and regulates protein synthesis throughout the cell, controlling the growth and development of the cell.

The cytoplasm of a neuron contains organelles (endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, ribosomes, etc.).

Ribosomes synthesize proteins, some of which remain in the cell, the other part is intended for removal from the cell. In addition, ribosomes produce elements of the molecular machinery for most cellular functions: enzymes, carrier proteins, receptors, membrane proteins, etc.

The endoplasmic reticulum is a system of channels and membrane-surrounded spaces (large, flat, called cisterns, and small, called vesicles or vesicles). There are smooth and rough endoplasmic reticulum. The latter contains ribosomes

The function of the Golgi apparatus is to store, concentrate and package secretory proteins.

In addition to systems that produce and transport various substances, the cell has an internal digestive system consisting of lysosomes that do not have a specific shape. They contain a variety of hydrolytic enzymes that break down and digest a variety of compounds occurring both inside and outside the cell.

Mitochondria are the most complex organ of the cell after the nucleus. Its function is the production and delivery of energy necessary for the life of cells.

Most of the body's cells are capable of metabolizing various sugars, and energy is either released or stored in the cell in the form of glycogen. However, nerve cells in the brain use glucose exclusively, since all other substances are retained by the blood-brain barrier. Most of them lack the ability to store glycogen, which increases their dependence on blood glucose and oxygen for energy. Therefore, nerve cells have the largest number of mitochondria.

The neuroplasm contains special-purpose organelles: microtubules and neurofilaments, which differ in size and structure. Neurofilaments are found only in nerve cells and represent the internal skeleton of the neuroplasm. Microtubules stretch along the axon along the internal cavities from the soma to the end of the axon. These organelles distribute biologically active substances (Fig. 1 A and B). Intracellular transport between the cell body and the processes extending from it can be retrograde - from nerve endings to the cell body and orthograde - from the cell body to the endings.

Rice. 1 A. Internal structure of a neuron

A distinctive feature of neurons is the presence of mitochondria in the axon as an additional source of energy and neurofibrils. Adult neurons are not capable of division.

Each neuron has an extended central body - the soma and processes - dendrites and axon. The cell body is enclosed in a cell membrane and contains a nucleus and nucleolus, maintaining the integrity of the membranes of the cell body and its processes, ensuring the conduction of nerve impulses. In relation to the processes, the soma performs a trophic function, regulating the metabolism of the cell. Impulses travel along dendrites (afferent processes) to the body of the nerve cell, and through axons (efferent processes) from the body of the nerve cell to other neurons or organs.

Most dendrites (dendron - tree) are short, highly branched processes. Their surface increases significantly due to small outgrowths - spines. An axon (axis - process) is often a long, slightly branched process.

Each neuron has only one axon, the length of which can reach several tens of centimeters. Sometimes lateral processes - collaterals - extend from the axon. The endings of the axon usually branch and are called terminals. The place where the axon emerges from the cell soma is called the axonal hillock.

Rice. 1 B. External structure of a neuron

There are several classifications of neurons based on different characteristics: the shape of the soma, the number of processes, the functions and effects that the neuron has on other cells.

Depending on the shape of the soma, granular (ganglionic) neurons are distinguished, in which the soma has a rounded shape; pyramidal neurons of different sizes - large and small pyramids; stellate neurons; fusiform neurons (Fig. 2 A).

Based on the number of processes, unipolar neurons are distinguished, having one process extending from the cell soma; pseudounipolar neurons (such neurons have a T-shaped branching process); bipolar neurons, which have one dendrite and one axon; and multipolar neurons, which have several dendrites and one axon (Fig. 2 B).

Rice. 2. Classification of neurons according to the shape of the soma and the number of processes

Unipolar neurons are located in sensory nodes (for example, spinal, trigeminal) and are associated with such types of sensitivity as pain, temperature, tactile, a sense of pressure, vibration, etc.

These cells, although called unipolar, actually have two processes that fuse near the cell body.

Bipolar cells are characteristic of the visual, auditory and olfactory systems

Multipolar cells have a varied body shape - spindle-shaped, basket-shaped, stellate, pyramidal - small and large.

According to the functions they perform, neurons are divided into: afferent, efferent and intercalary (contact).

Afferent neurons are sensory (pseudo-unipolar), their somas are located outside the central nervous system in ganglia (spinal or cranial). The shape of the soma is granular. Afferent neurons have one dendrite that connects to receptors (skin, muscle, tendon, etc.). Through dendrites, information about the properties of stimuli is transmitted to the soma of the neuron and along the axon to the central nervous system.

Efferent (motor) neurons regulate the functioning of effectors (muscles, glands, tissues, etc.). These are multipolar neurons, their somas have a stellate or pyramidal shape, lying in the spinal cord or brain or in the ganglia of the autonomic nervous system. Short, abundantly branching dendrites receive impulses from other neurons, and long axons extend beyond the central nervous system and, as part of the nerve, go to effectors (working organs), for example, to skeletal muscle.

Interneurons (interneurons, contact neurons) make up the bulk of the brain. They communicate between afferent and efferent neurons and process information coming from receptors to the central nervous system. These are mainly multipolar stellate-shaped neurons.

Among the interneurons, neurons with long and short axons differ (Fig. 3 A, B).

The following are depicted as sensory neurons: a neuron whose process is part of the auditory fibers of the vestibulocochlear nerve (VIII pair), a neuron that responds to skin stimulation (SC). Interneurons are represented by amacrine (AmN) and bipolar (BN) cells of the retina, an olfactory bulb neuron (OLN), a locus coeruleus neuron (LPN), a pyramidal cell of the cerebral cortex (PN) and a stellate neuron (SN) of the cerebellum. A spinal cord motor neuron is depicted as a motor neuron.

Rice. 3 A. Classification of neurons according to their functions

Sensory neuron:

1 - bipolar, 2 - pseudobipolar, 3 - pseudounipolar, 4 - pyramidal cell, 5 - spinal cord neuron, 6 - neuron of the p. ambiguus, 7 - neuron of the nucleus of the hypoglossal nerve. Sympathetic neurons: 8 - from the stellate ganglion, 9 - from the superior cervical ganglion, 10 - from the intermediolateral column of the lateral horn of the spinal cord. Parasympathetic neurons: 11 - from the muscular plexus ganglion of the intestinal wall, 12 - from the dorsal nucleus of the vagus nerve, 13 - from the ciliary ganglion.

Based on the effect that neurons have on other cells, excitatory neurons and inhibitory neurons are distinguished. Excitatory neurons have an activating effect, increasing the excitability of the cells with which they are connected. Inhibitory neurons, on the contrary, reduce the excitability of cells, causing an inhibitory effect.

The space between neurons is filled with cells called neuroglia (the term glia means glue, the cells “glue” the components of the central nervous system into a single whole). Unlike neurons, neuroglial cells divide throughout a person's life. There are a lot of neuroglial cells; in some parts of the nervous system there are 10 times more of them than nerve cells. Macroglia cells and microglia cells are distinguished (Fig. 4).

Four main types of glial cells.

Neuron surrounded by various glial elements

1 - macroglial astrocytes

2 - oligodendrocytes macroglia

3 – microglia macroglia

Rice. 4. Macroglia and microglia cells

Macroglia include astrocytes and oligodendrocytes. Astrocytes have many processes that extend from the cell body in all directions, giving the appearance of a star. In the central nervous system, some processes end in a terminal stalk on the surface of blood vessels. Astrocytes lying in the white matter of the brain are called fibrous astrocytes due to the presence of many fibrils in the cytoplasm of their bodies and branches. In gray matter, astrocytes contain fewer fibrils and are called protoplasmic astrocytes. They serve as a support for nerve cells, provide repair to nerves after damage, isolate and unite nerve fibers and endings, and participate in metabolic processes that model the ionic composition and mediators. The assumptions that they are involved in the transport of substances from blood vessels to nerve cells and form part of the blood-brain barrier have now been rejected.

1. Oligodendrocytes are smaller than astrocytes, contain small nuclei, are more common in white matter, and are responsible for the formation of myelin sheaths around long axons. They act as an insulator and increase the speed of nerve impulses along the processes. The myelin sheath is segmental, the space between the segments is called the node of Ranvier (Fig. 5). Each of its segments, as a rule, is formed by one oligodendrocyte (Schwann cell), which, as it becomes thinner, twists around the axon. The myelin sheath is white (white matter) because the membranes of oligodendrocytes contain a fat-like substance - myelin. Sometimes one glial cell, forming processes, takes part in the formation of segments of several processes. It is assumed that oligodendrocytes carry out complex metabolic exchanges with nerve cells.

1 - oligodendrocyte, 2 - connection between the glial cell body and the myelin sheath, 4 - cytoplasm, 5 - plasma membrane, 6 - node of Ranvier, 7 - plasma membrane loop, 8 - mesaxon, 9 - scallop

Rice. 5A. Participation of oligodendrocyte in the formation of the myelin sheath

Four stages of “envelopment” of the axon (2) by a Schwann cell (1) and its wrapping with several double layers of membrane, which after compression form a dense myelin sheath, are presented.

Rice. 5 B. Scheme of formation of the myelin sheath.

The neuron soma and dendrites are covered with thin membranes that do not form myelin and constitute gray matter.

2. Microglia are represented by small cells capable of amoeboid movement. The function of microglia is to protect neurons from inflammation and infections (via the mechanism of phagocytosis - the capture and digestion of genetically foreign substances). Microglial cells deliver oxygen and glucose to neurons. In addition, they are part of the blood-brain barrier, which is formed by them and the endothelial cells that form the walls of blood capillaries. The blood-brain barrier traps macromolecules, limiting their access to neurons.

Nerve fibers and nerves

The long processes of nerve cells are called nerve fibers. Through them, nerve impulses can be transmitted over long distances up to 1 meter.

The classification of nerve fibers is based on morphological and functional characteristics.

Nerve fibers that have a myelin sheath are called myelinated (myelinated), and fibers that do not have a myelin sheath are called unmyelinated (non-myelinated).

Based on functional characteristics, afferent (sensory) and efferent (motor) nerve fibers are distinguished.

Nerve fibers extending beyond the nervous system form nerves. A nerve is a collection of nerve fibers. Each nerve has a sheath and a blood supply (Fig. 6).

1 - common nerve trunk, 2 - nerve fiber branches, 3 - nerve sheath, 4 - bundles of nerve fibers, 5 - myelin sheath, 6 - Schwann cell membrane, 7 - node of Ranvier, 8 - Schwann cell nucleus, 9 - axolemma.

Rice. 6 Structure of a nerve (A) and nerve fiber (B).

There are spinal nerves connected to the spinal cord (31 pairs) and cranial nerves (12 pairs) connected to the brain. Depending on the quantitative ratio of afferent and efferent fibers within one nerve, sensory, motor and mixed nerves are distinguished. In sensory nerves, afferent fibers predominate, in motor nerves, efferent fibers predominate, in mixed nerves, the quantitative ratio of afferent and efferent fibers is approximately equal. All spinal nerves are mixed nerves. Among the cranial nerves, there are three types of nerves listed above. I pair - olfactory nerves (sensitive), II pair - optic nerves (sensitive), III pair - oculomotor (motor), IV pair - trochlear nerves (motor), V pair - trigeminal nerves (mixed), VI pair - abducens nerves ( motor), VII pair - facial nerves (mixed), VIII pair - vestibulo-cochlear nerves (mixed), IX pair - glossopharyngeal nerves (mixed), X pair - vagus nerves (mixed), XI pair - accessory nerves (motor), XII pair - hypoglossal nerves (motor) (Fig. 7).

I - para-olfactory nerves,

II - para-optic nerves,

III - para-oculomotor nerves,

IV - paratrochlear nerves,

V - pair - trigeminal nerves,

VI - para-abducens nerves,

VII - parafacial nerves,

VIII - para-cochlear nerves,

IX - paraglossopharyngeal nerves,

X - pair - vagus nerves,

XI - para-accessory nerves,

XII - para-1,2,3,4 - roots of the upper spinal nerves.

Rice. 7, Diagram of the location of the cranial and spinal nerves

Gray and white matter of the nervous system

Fresh sections of the brain show that some structures are darker - this is the gray matter of the nervous system, and other structures are lighter - the white matter of the nervous system. The white matter of the nervous system is formed by myelinated nerve fibers, the gray matter by the unmyelinated parts of the neuron - somas and dendrites.

The white matter of the nervous system is represented by central tracts and peripheral nerves. The function of white matter is the transmission of information from receptors to the central nervous system and from one part of the nervous system to another.

The gray matter of the central nervous system is formed by the cerebellar cortex and the cerebral cortex, nuclei, ganglia and some nerves.

Nuclei are accumulations of gray matter in the thickness of white matter. They are located in different parts of the central nervous system: in the white matter of the cerebral hemispheres - subcortical nuclei, in the white matter of the cerebellum - cerebellar nuclei, some nuclei are located in the diencephalon, midbrain and medulla oblongata. Most nuclei are nerve centers that regulate one or another function of the body.

Ganglia are a collection of neurons located outside the central nervous system. There are spinal, cranial ganglia and ganglia of the autonomic nervous system. Ganglia are formed predominantly by afferent neurons, but they may include intercalary and efferent neurons.

Interaction of neurons

The place of functional interaction or contact of two cells (the place where one cell influences another cell) was called a synapse by the English physiologist C. Sherrington.

Synapses are peripheral and central. An example of a peripheral synapse is the neuromuscular synapse, where a neuron makes contact with a muscle fiber. Synapses in the nervous system are called central synapses when two neurons come into contact. There are five types of synapses, depending on what parts the neurons are in contact with: 1) axo-dendritic (the axon of one cell contacts the dendrite of another); 2) axo-somatic (the axon of one cell contacts the soma of another cell); 3) axo-axonal (the axon of one cell contacts the axon of another cell); 4) dendro-dendritic (the dendrite of one cell is in contact with the dendrite of another cell); 5) somo-somatic (the somas of two cells are in contact). The bulk of contacts are axo-dendritic and axo-somatic.

Synaptic contacts can be between two excitatory neurons, two inhibitory neurons, or between an excitatory and an inhibitory neuron. In this case, the neurons that have an effect are called presynaptic, and the neurons that are affected are called postsynaptic. The presynaptic excitatory neuron increases the excitability of the postsynaptic neuron. In this case, the synapse is called excitatory. The presynaptic inhibitory neuron has the opposite effect - it reduces the excitability of the postsynaptic neuron. Such a synapse is called inhibitory. Each of the five types of central synapses has its own morphological features, although the general scheme of their structure is the same.

Synapse structure

Let us consider the structure of a synapse using the example of an axo-somatic one. The synapse consists of three parts: the presynaptic terminal, the synaptic cleft and the postsynaptic membrane (Fig. 8 A, B).

A-Synaptic inputs of a neuron. Synaptic plaques at the endings of presynaptic axons form connections on the dendrites and body (soma) of the postsynaptic neuron.

Rice. 8 A. Structure of synapses

The presynaptic terminal is the extended part of the axon terminal. The synaptic cleft is the space between two neurons in contact. The diameter of the synaptic cleft is 10-20 nm. The membrane of the presynaptic terminal facing the synaptic cleft is called the presynaptic membrane. The third part of the synapse is the postsynaptic membrane, which is located opposite the presynaptic membrane.

The presynaptic terminal is filled with vesicles and mitochondria. The vesicles contain biologically active substances - mediators. Mediators are synthesized in the soma and transported via microtubules to the presynaptic terminal. The most common mediators are adrenaline, norepinephrine, acetylcholine, serotonin, gamma-aminobutyric acid (GABA), glycine and others. Typically, a synapse contains one of the transmitters in greater quantities compared to other transmitters. Synapses are usually designated by the type of mediator: adrenergic, cholinergic, serotonergic, etc.

The postsynaptic membrane contains special protein molecules - receptors that can attach molecules of mediators.

The synaptic cleft is filled with intercellular fluid, which contains enzymes that promote the destruction of neurotransmitters.

One postsynaptic neuron can have up to 20,000 synapses, some of which are excitatory, and some are inhibitory (Fig. 8 B).

B. Scheme of transmitter release and processes occurring in a hypothetical central synapse.

Rice. 8 B. Structure of synapses

In addition to chemical synapses, in which neurotransmitters are involved in the interaction of neurons, electrical synapses are found in the nervous system. In electrical synapses, the interaction of two neurons is carried out through biocurrents. The central nervous system is dominated by chemical stimuli.

In some interneuron synapses, electrical and chemical transmission occurs simultaneously - this is a mixed type of synapse.

The influence of excitatory and inhibitory synapses on the excitability of the postsynaptic neuron is summed up and the effect depends on the location of the synapse. The closer the synapses are located to the axonal hillock, the more effective they are. On the contrary, the further the synapses are located from the axonal hillock (for example, at the end of dendrites), the less effective they are. Thus, synapses located on the soma and axonal hillock influence the excitability of the neuron quickly and efficiently, while the influence of distant synapses is slow and smooth.

Neural networks

Thanks to synaptic connections, neurons are united into functional units - neural networks. Neural networks can be formed by neurons located at a short distance. Such a neural network is called local. In addition, neurons remote from each other from different areas of the brain can be combined into a network. The highest level of organization of neuronal connections reflects the connection of several areas of the central nervous system. This neural network is called by or system. There are descending and ascending paths. Along ascending pathways, information is transmitted from underlying areas of the brain to higher ones (for example, from the spinal cord to the cerebral cortex). Descending tracts connect the cerebral cortex with the spinal cord.

The most complex networks are called distribution systems. They are formed by neurons in different parts of the brain that control behavior, in which the body participates as a whole.

Some nerve networks provide convergence (convergence) of impulses on a limited number of neurons. Nervous networks can also be built according to the type of divergence (divergence). Such networks enable the transmission of information over considerable distances. In addition, neural networks provide integration (summarization or generalization) of various types of information (Fig. 9).

Rice. 9. Nervous tissue.

A large neuron with many dendrites receives information through a synaptic contact with another neuron (top left). The myelinated axon forms a synaptic contact with the third neuron (bottom). The surfaces of neurons are shown without the glial cells that surround the process towards the capillary (top right).

Reflex as the basic principle of the nervous system

One example of a nerve network would be a reflex arc, which is necessary for a reflex to occur. THEM. In 1863, Sechenov, in his work “Reflexes of the Brain,” developed the idea that the reflex is the basic principle of operation not only of the spinal cord, but also of the brain.

A reflex is the body's response to irritation with the participation of the central nervous system. Each reflex has its own reflex arc - the path along which excitation passes from the receptor to the effector (executive organ). Any reflex arc includes five components: 1) a receptor - a specialized cell designed to perceive a stimulus (sound, light, chemical, etc.), 2) an afferent pathway, which is represented by afferent neurons, 3) a section of the central nervous system , represented by the spinal cord or brain; 4) the efferent pathway consists of axons of efferent neurons extending beyond the central nervous system; 5) effector - working organ (muscle or gland, etc.).

The simplest reflex arc includes two neurons and is called monosynaptic (based on the number of synapses). A more complex reflex arc is represented by three neurons (afferent, intercalary and efferent) and is called three-neuron or disynaptic. However, most reflex arcs include a large number of interneurons and are called polysynaptic (Fig. 10 A, B).

Reflex arcs can pass through the spinal cord only (withdrawing the hand when touching a hot object) or through the brain only (closing the eyelids when a stream of air is directed at the face), or through both the spinal cord and the brain.

Rice. 10A. 1 - intercalary neuron; 2 - dendrite; 3 - neuron body; 4 - axon; 5 - synapse between sensory and interneurons; 6 - axon of a sensitive neuron; 7 - body of a sensitive neuron; 8 - axon of a sensitive neuron; 9 - axon of a motor neuron; 10 - body of the motor neuron; 11 - synapse between intercalary and motor neurons; 12 - receptor in the skin; 13 - muscle; 14 - sympathetic gaglia; 15 - intestine.

Rice. 10B. 1 - monosynaptic reflex arc, 2 - polysynaptic reflex arc, 3K - posterior root of the spinal cord, PC - anterior root of the spinal cord.

Rice. 10. Scheme of the structure of the reflex arc

Reflex arcs are closed into reflex rings using feedback connections. The concept of feedback and its functional role was indicated by Bell in 1826. Bell wrote that two-way connections are established between the muscle and the central nervous system. With the help of feedback, signals about the functional state of the effector are sent to the central nervous system.

The morphological basis of feedback is the receptors located in the effector and the afferent neurons associated with them. Thanks to feedback afferent connections, fine regulation of the effector’s work and an adequate response of the body to environmental changes are carried out.

Meninges

The central nervous system (spinal cord and brain) has three connective tissue membranes: hard, arachnoid and soft. The outermost of these is the dura mater (it fuses with the periosteum lining the surface of the skull). The arachnoid membrane lies under the dura mater. It is pressed tightly against the hard surface and there is no free space between them.

Directly adjacent to the surface of the brain is the pia mater, which contains many blood vessels that supply the brain. Between the arachnoid and soft membranes there is a space filled with liquid - cerebrospinal fluid. The composition of cerebrospinal fluid is close to blood plasma and intercellular fluid and plays an anti-shock role. In addition, the cerebrospinal fluid contains lymphocytes that provide protection against foreign substances. It is also involved in the metabolism between the cells of the spinal cord, brain and blood (Fig. 11 A).

1 - dentate ligament, the process of which passes through the arachnoid membrane located on the side, 1a - dentate ligament attached to the dura mater of the spinal cord, 2 - arachnoid membrane, 3 - posterior root passing in the canal formed by the soft and arachnoid membranes, For - posterior root passing through the hole in the dura mater of the spinal cord, 36 - dorsal branches of the spinal nerve passing through the arachnoid membrane, 4 - spinal nerve, 5 - spinal ganglion, 6 - dura mater of the spinal cord, 6a - dura mater turned to the side , 7 - pia mater of the spinal cord with the posterior spinal artery.

Rice. 11A. Spinal cord membranes

Brain cavities

Inside the spinal cord is the spinal canal, which, passing into the brain, expands in the medulla oblongata and forms the fourth ventricle. At the level of the midbrain, the ventricle passes into a narrow canal - the aqueduct of Sylvius. In the diencephalon, the Sylvian aqueduct expands, forming the cavity of the third ventricle, which smoothly passes at the level of the cerebral hemispheres into the lateral ventricles (I and II). All of the listed cavities are also filled with cerebrospinal fluid (Fig. 11 B)

Figure 11B. Diagram of the ventricles of the brain and their relationship to the surface structures of the cerebral hemispheres.

a - cerebellum, b - occipital pole, c - parietal pole, d - frontal pole, e - temporal pole, f - medulla oblongata.

1 - lateral opening of the fourth ventricle (Lushka's foramen), 2 - lower horn of the lateral ventricle, 3 - aqueduct, 4 - recessusinfundibularis, 5 - recrssusopticus, 6 - interventricular foramen, 7 - anterior horn of the lateral ventricle, 8 - central part of the lateral ventricle, 9 - fusion of the visual tuberosities (massainter-melia), 10 - third ventricle, 11 - recessus pinealis, 12 - entrance to the lateral ventricle, 13 - posterior pro of the lateral ventricle, 14 - fourth ventricle.

Rice. 11. Meninges (A) and cavities of the brain (B)

SECTION II. STRUCTURE OF THE CENTRAL NERVOUS SYSTEM

Spinal cord

External structure of the spinal cord

The spinal cord is a flattened cord located in the spinal canal. Depending on the parameters of the human body, its length is 41-45 cm, average diameter is 0.48-0.84 cm, weight is about 28-32 g. In the center of the spinal cord there is a spinal canal filled with cerebrospinal fluid, and by the anterior and posterior longitudinal grooves it is divided into the right and left half.

In front, the spinal cord passes into the brain, and in the back it ends with the conus medullaris at the level of the 2nd vertebra of the lumbar spine. A connective tissue filum terminale (a continuation of the terminal membranes) departs from the conus medullaris, which attaches the spinal cord to the coccyx. The filum terminale is surrounded by nerve fibers (cauda equina) (Fig. 12).

There are two thickenings on the spinal cord - cervical and lumbar, from which nerves arise that innervate, respectively, the skeletal muscles of the arms and legs.

The spinal cord is divided into cervical, thoracic, lumbar and sacral sections, each of which is divided into segments: cervical - 8 segments, thoracic - 12, lumbar - 5, sacral 5-6 and 1 - coccygeal. Thus, the total number of segments is 31 (Fig. 13). Each segment of the spinal cord has paired spinal roots - anterior and posterior. Through the dorsal roots, information from receptors in the skin, muscles, tendons, ligaments, and joints enters the spinal cord, which is why the dorsal roots are called sensory (sensitive). Transection of the dorsal roots turns off tactile sensitivity, but does not lead to loss of movement.

a - front view (its ventral surface);

b - rear view (its dorsal surface).

The dura and arachnoid membranes are cut. The choroid is removed. Roman numerals indicate the order of cervical (c), thoracic (th), lumbar (t)

and sacral(s) spinal nerves.

1 - cervical thickening

2 - spinal ganglion

3 - hard shell

4 - lumbar thickening

5 - conus medullaris

6 - terminal thread

Rice. 13. Spinal cord and spinal nerves (31 pairs).

Along the anterior roots of the spinal cord, nerve impulses travel to the skeletal muscles of the body (except for the muscles of the head), causing them to contract, which is why the anterior roots are called motor or motor. After cutting the anterior roots on one side, there is a complete shutdown of motor reactions, while sensitivity to touch or pressure remains.

The anterior and posterior roots of each side of the spinal cord unite to form the spinal nerves. Spinal nerves are called segmental; their number corresponds to the number of segments and is 31 pairs (Fig. 14)

The distribution of spinal nerve zones by segment was established by determining the size and boundaries of the skin areas (dermatomes) innervated by each nerve. Dermatomes are located on the surface of the body according to a segmental principle. Cervical dermatomes include the back surface of the head, neck, shoulders and anterior surface of the forearms. Thoracic sensory neurons innervate the remaining surface of the forearm, chest, and most of the abdomen. Sensory fibers from the lumbar, sacral, and coccygeal segments extend to the rest of the abdomen and legs.

Rice. 14. Scheme of dermatomes. Innervation of the body surface by 31 pairs of spinal nerves (C - cervical, T - thoracic, L - lumbar, S - sacral).

Internal structure of the spinal cord

The spinal cord is built according to the nuclear type. There is gray matter around the spinal canal, and white matter at the periphery. Gray matter is formed by neuron somas and branching dendrites that do not have myelin sheaths. White matter is a collection of nerve fibers covered with myelin sheaths.

In the gray matter, anterior and posterior horns are distinguished, between which lies the interstitial zone. There are lateral horns in the thoracic and lumbar regions of the spinal cord.

The gray matter of the spinal cord is formed by two groups of neurons: efferent and intercalary. The bulk of the gray matter consists of interneurons (up to 97%) and only 3% are efferent neurons or motor neurons. Motor neurons are located in the anterior horns of the spinal cord. Among them, a- and g-motoneurons are distinguished: a-motoneurons innervate skeletal muscle fibers and are large cells with relatively long dendrites; g-motoneurons are small cells and innervate muscle receptors, increasing their excitability.

Interneurons are involved in information processing, ensuring coordinated operation of sensory and motor neurons, and also connect the right and left halves of the spinal cord and its various segments (Fig. 15 A, B, C)

Rice. 15A. 1 - white matter of the brain; 2 - spinal canal; 3 - posterior longitudinal groove; 4 - posterior root of the spinal nerve; 5 – spinal node; 6 - spinal nerve; 7 - gray matter of the brain; 8 - anterior root of the spinal nerve; 9 - anterior longitudinal groove

Rice. 15B. Gray matter nuclei in the thoracic region

1,2,3 - sensitive nuclei of the posterior horn; 4, 5 - intercalary nuclei of the lateral horn; 6,7, 8,9,10 - motor nuclei of the anterior horn; I, II, III - anterior, lateral and posterior cords of white matter.

The contacts between sensory, intercalary and motor neurons in the gray matter of the spinal cord are depicted.

Rice. 15. Cross section of the spinal cord

Spinal cord pathways

The white matter of the spinal cord surrounds the gray matter and forms the columns of the spinal cord. There are front, rear and side pillars. The columns are tracts of the spinal cord formed by long axons of neurons running up towards the brain (ascending tracts) or downwards from the brain to lower segments of the spinal cord (descending tracts).

The ascending tracts of the spinal cord transmit information from receptors in muscles, tendons, ligaments, joints and skin to the brain. The ascending pathways are also conductors of temperature and pain sensitivity. All ascending pathways intersect at the level of the spinal cord (or brain). Thus, the left half of the brain (the cerebral cortex and the cerebellum) receives information from the receptors on the right half of the body and vice versa.

Main ascending paths: from the mechanoreceptors of the skin and the receptors of the musculoskeletal system - these are muscles, tendons, ligaments, joints - the Gaulle and Burdach bundles or, respectively, the gentle and wedge-shaped bundles are represented by the posterior columns of the spinal cord.

From these same receptors, information enters the cerebellum along two pathways represented by lateral columns, which are called the anterior and posterior spinocerebellar tracts. In addition, two more pathways pass through the lateral columns - these are the lateral and anterior spinothalamic tracts, which transmit information from temperature and pain sensitivity receptors.

The posterior columns provide faster transmission of information about the localization of stimuli than the lateral and anterior spinothalamic tracts (Fig. 16 A).

1 - Gaulle's bundle, 2 - Burdach's bundle, 3 - dorsal spinocerebellar tract, 4 - ventral spinocerebellar tract. Neurons of groups I-IV.

Rice. 16A. Ascending tracts of the spinal cord

Descending Paths, passing through the anterior and lateral columns of the spinal cord, are motor, as they affect the functional state of the skeletal muscles of the body. The pyramidal tract begins mainly in the motor cortex of the hemispheres and passes to the medulla oblongata, where most of the fibers cross and pass to the opposite side. After this, the pyramidal tract is divided into lateral and anterior bundles: the anterior and lateral pyramidal tracts, respectively. Most pyramidal tract fibers terminate on interneurons, and about 20% form synapses on motor neurons. The pyramidal influence is exciting. Reticulospinal path, rubrospinal way and vestibulospinal the pathway (extrapyramidal system) begins respectively from the nuclei of the reticular formation, the brainstem, the red nuclei of the midbrain and the vestibular nuclei of the medulla oblongata. These pathways run in the lateral columns of the spinal cord and are involved in coordinating movements and ensuring muscle tone. Extrapyramidal tracts, like the pyramidal ones, are crossed (Fig. 16 B).

The main descending spinal tracts are the pyramidal (lateral and anterior corticospinal tracts) and extra pyramidal (rubrospinal, reticulospinal and vestibulospinal tracts) systems.

Rice. 16 B. Diagram of pathways

Thus, the spinal cord performs two important functions: reflex and conduction. The reflex function is carried out due to the motor centers of the spinal cord: motor neurons of the anterior horns ensure the functioning of the skeletal muscles of the body. At the same time, maintaining muscle tone, coordinating the work of the flexor-extensor muscles that underlie the movements, and maintaining the constancy of the posture of the body and its parts are maintained (Fig. 17 A, B, C). Motor neurons located in the lateral horns of the thoracic segments of the spinal cord provide respiratory movements (inhalation-exhalation, regulating the work of the intercostal muscles). Motor neurons of the lateral horns of the lumbar and sacral segments represent the motor centers of smooth muscles that are part of the internal organs. These are the centers of urination, defecation, and the functioning of the genital organs.

Rice. 17A. The arc of the tendon reflex.

Rice. 17B. Arcs of the flexion and cross-extensor reflex.

Rice. 17V. Elementary diagram of an unconditioned reflex.

Nerve impulses arising from irritation of the receptor (p) along afferent fibers (afferent nerve, only one such fiber is shown) go to the spinal cord (1), where through the intercalary neuron they are transmitted to efferent fibers (efferent nerve), along which they reach effector. The dotted lines represent the spread of excitation from the lower parts of the central nervous system to its higher parts (2, 3,4) up to the cerebral cortex (5) inclusive. The resulting change in the state of the higher parts of the brain in turn affects (see arrows) the efferent neuron, influencing the final result of the reflex response.

Rice. 17. Reflex function of the spinal cord

The conduction function is performed by the spinal tracts (Fig. 18 A, B, C, D, E).

Rice. 18A. Rear pillars. This circuit, formed by three neurons, transmits information from pressure and touch receptors to the somatosensory cortex.

Rice. 18B. Lateral spinothalamic tract. Along this path, information from temperature and pain receptors reaches large areas of the coronary brain.

Rice. 18V. Anterior spinothalamic tract. Along this pathway, information from pressure and touch receptors, as well as pain and temperature receptors, enters the somatosensory cortex.

Rice. 18G. Extrapyramidal system. Rubrospinal and reticulospinal tracts, which are part of the multineural extrapyramidal tract running from the cerebral cortex to the spinal cord.

Rice. 18D. Pyramidal or corticospinal tract

Rice. 18. Conductive function of the spinal cord

SECTION III. BRAIN.

General diagram of the structure of the brain (Fig. 19)

Brain

Figure 19A. Brain

1. Frontal cortex (cognitive area)

2. Motor cortex

3. Visual cortex

4. Cerebellum 5. Auditory cortex

Figure 19B. Side view

Figure 19B. The main formations of the medal surface of the brain in a midsagittal section.

Fig 19G. Lower surface of the brain

Rice. 19. Structure of the brain

hindbrain

The hindbrain, including the medulla oblongata and the pons, is a phylogenetically ancient region of the central nervous system, retaining the features of a segmental structure. The hindbrain contains nuclei and ascending and descending pathways. Afferent fibers from vestibular and auditory receptors, from receptors in the skin and muscles of the head, from receptors in internal organs, as well as from higher structures of the brain enter the hindbrain along the pathways. The hindbrain contains the nuclei of the V-XII pairs of cranial nerves, some of which innervate the facial and oculomotor muscles.

Medulla

The medulla oblongata is located between the spinal cord, the pons and the cerebellum (Fig. 20). On the ventral surface of the medulla oblongata, the anterior median groove runs along the midline; on its sides there are two cords - pyramids; olives lie on the side of the pyramids (Fig. 20 A-B).

Rice. 20A. 1 - cerebellum 2 - cerebellar peduncles 3 - pons 4 - medulla oblongata

Rice. 20V. 1 - bridge 2 - pyramid 3 - olive 4 - anterior medial fissure 5 - anterior lateral groove 6 - cross of the anterior cord 7 - anterior cord 8 - lateral cord

Rice. 20. Medulla oblongata

On the posterior side of the medulla oblongata there is a posterior medial groove. On its sides lie the posterior cords, which go to the cerebellum as part of the hind legs.

Gray matter of the medulla oblongata

The medulla oblongata contains the nuclei of four pairs of cranial nerves. These include the nuclei of the glossopharyngeal, vagus, accessory and hypoglossal nerves. In addition, the tender, wedge-shaped nuclei and cochlear nuclei of the auditory system, the nuclei of the inferior olives and the nuclei of the reticular formation (giant cell, parvocellular and lateral), as well as the respiratory nuclei are distinguished.

The nuclei of the hypoglossal (XII pair) and accessory (XI pair) nerves are motor, innervating the muscles of the tongue and the muscles that move the head. The nuclei of the vagus (X pair) and glossopharyngeal (IX pair) nerves are mixed; they innervate the muscles of the pharynx, larynx, and thyroid gland, and regulate swallowing and chewing. These nerves consist of afferent fibers coming from the receptors of the tongue, larynx, trachea and from the receptors of the internal organs of the chest and abdominal cavity. Efferent nerve fibers innervate the intestines, heart and blood vessels.

The nuclei of the reticular formation not only activate the cerebral cortex, maintaining consciousness, but also form the respiratory center, which ensures respiratory movements.

Thus, some of the nuclei of the medulla oblongata regulate vital functions (these are the nuclei of the reticular formation and the nuclei of the cranial nerves). The other part of the nuclei is part of the ascending and descending pathways (grass and cuneate nuclei, cochlear nuclei of the auditory system) (Fig. 21).

2 - wedge-shaped nucleus;

3 - the end of the fibers of the posterior cords of the spinal cord;

4 - internal arcuate fibers - the second neuron of the propria pathway of the cortical direction;

5 - the intersection of loops is located in the inter-olive loop layer;

6 - medial loop - continuation of the internal arcuate voles

7 - seam, formed by the intersection of loops;

8 - olive core - intermediate core of balance;

9 - pyramidal paths;

10 - central channel.

Rice. 21. Internal structure of the medulla oblongata

White matter of the medulla oblongata

The white matter of the medulla oblongata is formed by long and short nerve fibers

Long nerve fibers are part of the descending and ascending pathways. Short nerve fibers ensure coordinated functioning of the right and left halves of the medulla oblongata.

Pyramids medulla oblongata - part descending pyramidal tract, going to the spinal cord and ending at interneurons and motor neurons. In addition, the rubrospinal tract passes through the medulla oblongata. The descending vestibulospinal and reticulospinal tracts originate in the medulla oblongata, respectively, from the vestibular and reticular nuclei.

The ascending spinocerebellar tracts pass through olives medulla oblongata and through the cerebral peduncles and transmit information from the receptors of the musculoskeletal system to the cerebellum.

Tender And wedge-shaped nuclei The medulla oblongata is part of the spinal cord tracts of the same name, running through the visual thalamus of the diencephalon to the somatosensory cortex.

Through cochlear auditory nuclei and through vestibular nuclei ascending sensory pathways from auditory and vestibular receptors. In the projection zone of the temporal cortex.

Thus, the medulla oblongata regulates the activity of many vital functions of the body. Therefore, the slightest damage to the medulla oblongata (trauma, swelling, hemorrhage, tumors) usually leads to death.

Pons

The pons is a thick ridge that borders the medulla oblongata and the cerebellar peduncles. The ascending and descending tracts of the medulla oblongata pass through the bridge without interruption. At the junction of the pons and the medulla oblongata, the vestibulocochlear nerve (VIII pair) emerges. The vestibulocochlear nerve is sensitive and transmits information from the auditory and vestibular receptors of the inner ear. In addition, the pons contains mixed nerves, the nuclei of the trigeminal nerve (V pair), abducens nerve (VI pair), and facial nerve (VII pair). These nerves innervate the facial muscles, scalp, tongue, and lateral rectus muscles of the eye.

On a cross section, the bridge consists of a ventral and dorsal part - between them the border is the trapezoidal body, the fibers of which are attributed to the auditory tract. In the region of the trapezius body there is a medial parabranchial nucleus, which is connected with the dentate nucleus of the cerebellum. The pontine nucleus proper communicates the cerebellum with the cerebral cortex. In the dorsal part of the bridge lie the nuclei of the reticular formation and the ascending and descending pathways of the medulla oblongata continue.

The bridge performs complex and varied functions aimed at maintaining posture and maintaining body balance in space when changing speed.

Vestibular reflexes are very important, the reflex arcs of which pass through the bridge. They provide tone to the neck muscles, stimulation of the autonomic centers, breathing, heart rate, and activity of the gastrovascular tract.

The nuclei of the trigeminal, glossopharyngeal, vagus and pontine nerves are associated with the grasping, chewing and swallowing of food.

Neurons of the reticular formation of the bridge play a special role in activating the cerebral cortex and limiting the sensory influx of nerve impulses during sleep (Fig. 22, 23)

Rice. 22. Medulla oblongata and pons.

A. Top view (dorsal side).

B. Side view.

B. View from below (from the ventral side).

1 - uvula, 2 - anterior medullary velum, 3 - median eminence, 4 - superior fossa, 5 - superior cerebellar peduncle, 6 - middle cerebellar peduncle, 7 - facial tubercle, 8 - inferior cerebellar peduncle, 9 - auditory tubercle, 10 - brain stripes, 11 - band of the fourth ventricle, 12 - triangle of the hypoglossal nerve, 13 - triangle of the vagus nerve, 14 - areapos-terma, 15 - obex, 16 - tubercle of the sphenoid nucleus, 17 - tubercle of the tender nucleus, 18 - lateral cord, 19 - posterior lateral sulcus, 19 a - anterior lateral sulcus, 20 - sphenoid cord, 21 - posterior intermediate sulcus, 22 - tender cord, 23 - posterior median sulcus, 23 a - pons - base), 23 b - pyramid of the medulla oblongata, 23 c -olive, 23 g - decussation of pyramids, 24 - cerebral peduncle, 25 - lower tubercle, 25 a - handle of the lower tubercle, 256 - superior tubercle

1 - trapezoid body 2 - nucleus of the superior olive 3 - dorsal contains the nuclei of VIII, VII, VI, V pairs of cranial nerves 4 - medal part of the pons 5 - ventral part of the pons contains its own nuclei and pons 7 - transverse nuclei of the pons 8 - pyramidal tracts 9 - middle cerebellar peduncle.

Rice. 23. Diagram of the internal structure of the bridge in a frontal section

Cerebellum

The cerebellum is a part of the brain located behind the cerebral hemispheres above the medulla oblongata and the pons.

Anatomically, the cerebellum is divided into a middle part - the vermis, and two hemispheres. With the help of three pairs of legs (lower, middle and superior), the cerebellum is connected to the brain stem. The lower legs connect the cerebellum with the medulla oblongata and spinal cord, the middle ones with the pons, and the upper ones with the mesencephalon and diencephalon (Fig. 24).

1 - vermis 2 - central lobule 3 - vermis uvula 4 - anterior veslus cerebellum 5 - superior hemisphere 6 - anterior cerebellar peduncle 8 - peduncle flocculus 9 – flocculus 10 - superior semilunar lobule 11 - inferior semilunar lobule 12 - inferior hemisphere 13 - digastric lobule 14 - cerebellar lobule 15 - cerebellar tonsil 16 - vermis pyramid 17 - wing of the central lobule 18 - node 19 - apex 20 - groove 21 - vermis hub 22 - vermis tubercle 23 - quadrangular lobule.

Rice. 24. Internal structure of the cerebellum

The cerebellum is built according to the nuclear type - the surface of the hemispheres is represented by gray matter, which makes up the new cortex. The cortex forms convolutions that are separated from each other by grooves. Under the cerebellar cortex there is white matter, in the thickness of which the paired cerebellar nuclei are distinguished (Fig. 25). These include tent cores, spherical core, cork core, jagged core. The tent nuclei are associated with the vestibular apparatus, the spherical and cortical nuclei are associated with the movement of the torso, and the dentate nucleus is associated with the movement of the limbs.

1- anterior cerebellar peduncles; 2 - tent cores; 3 - dentate core; 4 - corky core; 5 - white substance; 6 - cerebellar hemispheres; 7 – worm; 8 globular nucleus

Rice. 25. Cerebellar nuclei

The cerebellar cortex is of the same type and consists of three layers: molecular, ganglion and granular, in which there are 5 types of cells: Purkinje cells, basket, stellate, granular and Golgi cells (Fig. 26). In the superficial, molecular layer, there are dendritic branches of Purkinje cells, which are one of the most complex neurons in the brain. Dendritic processes are abundantly covered with spines, indicating a large number of synapses. In addition to Purkinje cells, this layer contains many axons of parallel nerve fibers (T-shaped branching axons of granular cells). In the lower part of the molecular layer there are bodies of basket cells, the axons of which form synaptic contacts in the region of the axon hillocks of Purkinje cells. The molecular layer also contains stellate cells.

A. Purkinje cell. B. Granule cells.

B. Golgi cell.

Rice. 26. Types of cerebellar neurons.

Below the molecular layer is the ganglion layer, which contains the bodies of Purkinje cells.

The third layer - granular - is represented by the bodies of interneurons (granule cells or granular cells). In the granular layer there are also Golgi cells, the axons of which rise into the molecular layer.

Only two types of afferent fibers enter the cerebellar cortex: climbing and mossy, which carry nerve impulses to the cerebellum. Each climbing fiber has contact with one Purkinje cell. The branches of the mossy fiber form contacts mainly with granule neurons, but do not contact Purkinje cells. Mossy fiber synapses are excitatory (Fig. 27).

Excitatory impulses arrive to the cortex and nuclei of the cerebellum via both climbing and mossy fibers. From the cerebellum, signals come only from Purkinje cells (P), which inhibit the activity of neurons in nuclei 1 of the cerebellum (P). The intrinsic neurons of the cerebellar cortex include excitatory granule cells (3) and inhibitory basket neurons (K), Golgi neurons (G) and stellate neurons (Sv). The arrows indicate the direction of movement of nerve impulses. There are both exciting (+) and; inhibitory (-) synapses.

Rice. 27. Neural circuit of the cerebellum.

Thus, the cerebellar cortex includes two types of afferent fibers: climbing and mossy. These fibers transmit information from tactile receptors and receptors of the musculoskeletal system, as well as from all brain structures that regulate the motor function of the body.

The efferent influence of the cerebellum is carried out through the axons of Purkinje cells, which are inhibitory. The axons of Purkinje cells exert their influence either directly on motor neurons of the spinal cord, or indirectly through neurons of the cerebellar nuclei or other motor centers.

In humans, due to upright posture and work activity, the cerebellum and its hemispheres reach their greatest development and size.

When the cerebellum is damaged, imbalances and muscle tone are observed. The nature of the violations depends on the location of the damage. Thus, when the tent cores are damaged, the balance of the body is disrupted. This manifests itself in a staggering gait. If the worm, cork and spherical nuclei are damaged, the work of the muscles of the neck and torso is disrupted. The patient has difficulty eating. If the hemispheres and dentate nucleus are damaged, the work of the muscles of the limbs (tremor) becomes difficult, and his professional activities become difficult.

In addition, in all patients with cerebellar damage due to impaired coordination of movements and tremor (shaking), fatigue quickly occurs.

Midbrain

The midbrain, like the medulla oblongata and the pons, belongs to the stem structures (Fig. 28).

1 - commissure of leashes

2 - leash

3 - pineal gland

4 - superior colliculus of the midbrain

5 - medial geniculate body

6 - lateral geniculate body

7 - inferior colliculus of the midbrain

8 - superior cerebellar peduncles

9 - middle cerebellar peduncles

10 - inferior cerebellar peduncles

11- medulla oblongata

Rice. 28. Hindbrain

The midbrain consists of two parts: the roof of the brain and the cerebral peduncles. The roof of the midbrain is represented by the quadrigemina, in which the superior and inferior colliculi are distinguished. In the thickness of the cerebral peduncles, paired clusters of nuclei are distinguished, called the substantia nigra and the red nucleus. Through the midbrain there are ascending pathways to the diencephalon and cerebellum and descending pathways from the cerebral cortex, subcortical nuclei and diencephalon to the nuclei of the medulla oblongata and spinal cord.

In the lower colliculus of the quadrigemina there are neurons that receive afferent signals from auditory receptors. Therefore, the lower tubercles of the quadrigeminal are called the primary auditory center. The reflex arc of the indicative auditory reflex passes through the primary auditory center, which manifests itself in turning the head towards the acoustic signal.

The superior colliculus is the primary visual center. The neurons of the primary visual center receive afferent impulses from photoreceptors. The superior colliculus provides an indicative visual reflex - turning the head towards the visual stimulus.

The nuclei of the lateral and oculomotor nerves take part in the implementation of orientation reflexes, which innervate the muscles of the eyeball, ensuring its movement.

The red nucleus contains neurons of different sizes. The descending rubrospinal tract begins from the large neurons of the red nucleus, which affects motor neurons and finely regulates muscle tone.

The neurons of the substantia nigra contain the pigment melanin and give this nucleus its dark color. The substantia nigra, in turn, sends signals to neurons in the reticular nuclei of the brain stem and subcortical nuclei.

The substantia nigra is involved in complex coordination of movements. It contains dopaminergic neurons, i.e. releasing dopamine as a mediator. One part of these neurons regulates emotional behavior, the other plays an important role in the control of complex motor acts. Damage to the substantia nigra, leading to degeneration of dopaminergic fibers, causes the inability to begin performing voluntary movements of the head and arms when the patient sits quietly (Parkinson's disease) (Fig. 29 A, B).

Rice. 29A. 1 - colliculus 2 - aqueduct of the cerebellum 3 - central gray matter 4 - substantia nigra 5 - medial sulcus of the cerebral peduncle

Rice. 29B. Diagram of the internal structure of the midbrain at the level of the inferior colliculi (frontal section)

1 - nucleus of the inferior colliculus, 2 - motor tract of the extrapyramidal system, 3 - dorsal decussation of the tegmentum, 4 - red nucleus, 5 - red nucleus - spinal tract, 6 - ventral decussation of the tegmentum, 7 - medial lemniscus, 8 - lateral lemniscus, 9 - reticular formation, 10 - medial longitudinal fasciculus, 11 - nucleus of the midbrain tract of the trigeminal nerve, 12 - nucleus of the lateral nerve, I-V - descending motor tracts of the cerebral peduncle

Rice. 29. Diagram of the internal structure of the midbrain

Diencephalon

The diencephalon forms the walls of the third ventricle. Its main structures are the visual tuberosities (thalamus) and the subtuberculous region (hypothalamus), as well as the supratubercular region (epithalamus) (Fig. 30 A, B).

Rice. 30 A. 1 - thalamus (visual thalamus) - the subcortical center of all types of sensitivity, the “sensory” of the brain; 2 - epithalamus (supratubercular region); 3 - metathalamus (foreign region).

Rice. 30 B. Circuits of the visual brain ( thalamencephalon ): a - top view b - rear and bottom view.

Thalamus (visual thalamus) 1 - anterior burf of the visual thalamus, 2 - cushion 3 - intertubercular fusion 4 - medullary strip of the visual thalamus

Epithalamus (supratubercular region) 5 - triangle of the leash, 6 - leash, 7 - commissure of the leash, 8 - pineal body (epiphysis)

Metathalamus (external region) 9 - lateral geniculate body, 10 - medial geniculate body, 11 - III ventricle, 12 - roof of the midbrain

Rice. 30. Visual Brain

Deep in the brain tissue of the diencephalon, the nuclei of the external and internal geniculate bodies are located. The outer border is formed by the white matter that separates the diencephalon from the telencephalon.

Thalamus (visual thalamus)

The neurons of the thalamus form 40 nuclei. Topographically, the nuclei of the thalamus are divided into anterior, median and posterior. Functionally, these nuclei can be divided into two groups: specific and nonspecific.

Specific nuclei are part of specific pathways. These are ascending pathways that transmit information from sensory organ receptors to the projection zones of the cerebral cortex.

The most important of the specific nuclei are the lateral geniculate body, which is involved in transmitting signals from photoreceptors, and the medial geniculate body, which transmits signals from auditory receptors.

The nonspecific ribs of the thalamus are classified as the reticular formation. They act as integrative centers and have a predominantly activating ascending effect on the cerebral cortex (Fig. 31 A, B)

1 - anterior group (olfactory); 2 - posterior group (visual); 3 - lateral group (general sensitivity); 4 - medial group (extrapyramidal system; 5 - central group (reticular formation).

Rice. 31B. Frontal section of the brain at the level of the middle of the thalamus. 1a - anterior nucleus of the visual thalamus. 16 - medial nucleus of the visual thalamus, 1c - lateral nucleus of the visual thalamus, 2 - lateral ventricle, 3 - fornix, 4 - caudate nucleus, 5 - internal capsule, 6 - external capsule, 7 - external capsule (capsula extrema), 8 - ventral nucleus thalamus optica, 9 - subthalamic nucleus, 10 - third ventricle, 11 - cerebral peduncle. 12 - bridge, 13 - interpeduncular fossa, 14 - hippocampal peduncle, 15 - inferior horn of the lateral ventricle. 16 - black substance, 17 - insula. 18 - pale ball, 19 - shell, 20 - Trout N fields; and b. 21 - interthalamic fusion, 22 - corpus callosum, 23 - tail of the caudate nucleus.

Figure 31. Diagram of groups of thalamus nuclei

Activation of neurons in the nonspecific nuclei of the thalamus is especially effective in causing pain signals (the thalamus is the highest center of pain sensitivity).

Damage to the nonspecific nuclei of the thalamus also leads to impairment of consciousness: loss of active communication between the body and the environment.

Subthalamus (hypothalamus)

The hypothalamus is formed by a group of nuclei located at the base of the brain. The nuclei of the hypothalamus are the subcortical centers of the autonomic nervous system of all vital functions of the body.

Topographically, the hypothalamus is divided into the preoptic area, the areas of the anterior, middle and posterior hypothalamus. All nuclei of the hypothalamus are paired (Fig. 32 A-D).

1 - aqueduct 2 - red nucleus 3 - tegmentum 4 - substantia nigra 5 - cerebral peduncle 6 - mastoid bodies 7 - anterior perforated substance 8 - oblique triangle 9 - infundibulum 10 - optic chiasm 11. optic nerve 12 - gray tubercle 13 - posterior perforated substance 14 - external geniculate body 15 - medial geniculate body 16 - cushion 17 - optic tract

Rice. 32A. Metathalamus and hypothalamus

a - bottom view; b - mid sagittal section.

Visual part (parsoptica): 1 - terminal plate; 2 - visual chiasm; 3 - visual tract; 4 - gray tubercle; 5 - funnel; 6 - pituitary gland;

Olfactory part: 7 - mamillary bodies - subcortical olfactory centers; 8 - the subcutaneous region in the narrow sense of the word is a continuation of the cerebral peduncles, contains the substantia nigra, the red nucleus and the Lewis body, which is a link in the extrapyramidal system and the vegetative center; 9 - subtubercular Monroe's groove; 10 - sella turcica, in the fossa of which the pituitary gland is located.

Rice. 32B. Subcutaneous region (hypothalamus)

Rice. 32V. Main nuclei of the hypothalamus

1 - nucleus supraopticus; 2 - nucleus preopticus; 3 - nucliusparaventricularis; 4 - nucleus in fundibularus; 5 - nucleuscorporismamillaris; 6 - visual chiasm; 7 - pituitary gland; 8 - gray tubercle; 9 - mastoid body; 10 bridge.

Rice. 32G. Scheme of the neurosecretory nuclei of the subthalamic region (Hypothalamus)

The preoptic area includes the periventricular, medial and lateral preoptic nuclei.

The anterior hypothalamus group includes the supraoptic, suprachiasmatic and paraventricular nuclei.

The middle hypothalamus makes up the ventromedial and dorsomedial nuclei.

In the posterior hypothalamus, the posterior hypothalamic, perifornical and mamillary nuclei are distinguished.

The connections of the hypothalamus are extensive and complex. Afferent signals to the hypothalamus come from the cerebral cortex, subcortical nuclei and thalamus. The main efferent pathways reach the midbrain, thalamus and subcortical nuclei.

The hypothalamus is the highest center for the regulation of the cardiovascular system, water-salt, protein, fat, and carbohydrate metabolism. This area of ​​the brain contains centers associated with the regulation of eating behavior. An important role of the hypothalamus is regulation. Electrical stimulation of the posterior nuclei of the hypothalamus leads to hyperthermia, as a result of increased metabolism.

The hypothalamus also takes part in maintaining the sleep-wake biorhythm.

The nuclei of the anterior hypothalamus are connected to the pituitary gland and transport biologically active substances that are produced by the neurons of these nuclei. Neurons of the preoptic nucleus produce releasing factors (statins and liberins) that control the synthesis and release of pituitary hormones.

Neurons of the preoptic, supraoptic, paraventricular nuclei produce true hormones - vasopressin and oxytocin, which descend along the axons of neurons to the neurohypophysis, where they are stored until released into the blood.

Neurons of the anterior pituitary gland produce 4 types of hormones: 1) somatotropic hormone, which regulates growth; 2) gonadotropic hormone, which promotes the growth of germ cells, the corpus luteum, and enhances milk production; 3) thyroid-stimulating hormone – stimulates the function of the thyroid gland; 4) adrenocorticotropic hormone - enhances the synthesis of hormones of the adrenal cortex.

The intermediate lobe of the pituitary gland secretes the hormone intermedin, which affects skin pigmentation.

The posterior lobe of the pituitary gland secretes two hormones - vasopressin, which affects the smooth muscles of the arterioles, and oxytocin, which acts on the smooth muscles of the uterus and stimulates milk secretion.

The hypothalamus also plays an important role in emotional and sexual behavior.

The epithalamus (pineal gland) includes the pineal gland. The pineal gland hormone, melatonin, inhibits the formation of gonadotropic hormones in the pituitary gland, and this in turn delays sexual development.

Forebrain

The forebrain consists of three anatomically separate parts - the cerebral cortex, white matter and subcortical nuclei.

In accordance with the phylogeny of the cerebral cortex, the ancient cortex (archicortex), old cortex (paleocortex) and new cortex (neocortex) are distinguished. The ancient cortex includes the olfactory bulbs, which receive afferent fibers from the olfactory epithelium, the olfactory tracts - located on the lower surface of the frontal lobe, and the olfactory tubercles - secondary olfactory centers.

The old cortex includes the cingulate cortex, hippocampal cortex, and amygdala.

All other areas of the cortex are neocortex. The ancient and old cortex is called the olfactory brain (Fig. 33).

The olfactory brain, in addition to functions related to smell, provides reactions of alertness and attention, and takes part in the regulation of the autonomic functions of the body. This system also plays an important role in the implementation of instinctive forms of behavior (eating, sexual, defensive) and the formation of emotions.

a - bottom view; b - on a sagittal section of the brain

Peripheral department: 1 - bulbusolfactorius (olfactory bulb; 2 - tractusolfactories (olfactory path); 3 - trigonumolfactorium (olfactory triangle); 4 - substantiaperforateanterior (anterior perforated substance).

Central section - convolutions of the brain: 5 - vaulted gyrus; 6 - hippocampus is located in the cavity of the lower horn of the lateral ventricle; 7 - continuation of the gray vestment of the corpus callosum; 8 - vault; 9 - transparent septum - conductive pathways of the olfactory brain.

Figure 33. Olfactory brain

Irritation of the structures of the old cortex affects the cardiovascular system and breathing, causes hypersexuality, and changes emotional behavior.

With electrical stimulation of the tonsil, effects associated with the activity of the digestive tract are observed: licking, chewing, swallowing, changes in intestinal motility. Irritation of the tonsil also affects the activity of internal organs - kidneys, bladder, uterus.

Thus, there is a connection between the structures of the old cortex and the autonomic nervous system, with processes aimed at maintaining the homeostasis of the internal environments of the body.

Finite brain

The telencephalon includes: the cerebral cortex, white matter and the subcortical nuclei located in its thickness.

The surface of the cerebral hemispheres is folded. Furrows - depressions divide it into lobes.

The central (Rolandian) sulcus separates the frontal lobe from the parietal lobe. The lateral (Sylvian) fissure separates the temporal lobe from the parietal and frontal lobes. The occipito-parietal sulcus forms the boundary between the parietal, occipital and temporal lobes (Fig. 34 A, B, Fig. 35)

1 - superior frontal gyrus; 2 - middle frontal gyrus; 3 - precentral gyrus; 4 - postcentral gyrus; 5 - inferior parietal gyrus; 6 - superior parietal gyrus; 7 - occipital gyrus; 8 - occipital groove; 9 - intraparietal sulcus; 10 - central groove; 11 - precentral gyrus; 12 - inferior frontal sulcus; 13 - superior frontal sulcus; 14 - vertical slot.

Rice. 34A. Brain from the dorsal surface

1 - olfactory groove; 2 - anterior perforated substance; 3 - hook; 4 - middle temporal sulcus; 5 - inferior temporal sulcus; 6 - seahorse groove; 7 - roundabout groove; 8 - calcarine groove; 9 - wedge; 10 - parahippocampal gyrus; 11 - occipitotemporal groove; 12 - inferior parietal gyrus; 13 - olfactory triangle; 14 - straight gyrus; 15 - olfactory tract; 16 - olfactory bulb; 17 - vertical slot.

Rice. 34B. Brain from the ventral surface

1 - central groove (Rolanda); 2 - lateral groove (Sylvian fissure); 3 - precentral sulcus; 4 - superior frontal sulcus; 5 - inferior frontal sulcus; 6 - ascending branch; 7 - anterior branch; 8 - postcentral groove; 9 - intraparietal sulcus; 10 - superior temporal sulcus; 11 - inferior temporal sulcus; 12 - transverse occipital groove; 13 - occipital groove.

Rice. 35. Grooves on the superolateral surface of the hemisphere (left side)

Thus, the grooves divide the hemispheres of the telencephalon into five lobes: the frontal, parietal, temporal, occipital and insular lobe, which is located under the temporal lobe (Fig. 36).

Rice. 36. Projection (marked with dots) and associative (light) zones of the cerebral cortex. Projection areas include the motor area (frontal lobe), somatosensory area (parietal lobe), visual area (occipital lobe), and auditory area (temporal lobe).

There are also grooves on the surface of each lobe.

There are three orders of furrows: primary, secondary and tertiary. The primary grooves are relatively stable and the deepest. These are the boundaries of large morphological parts of the brain. Secondary grooves extend from the primary ones, and tertiary ones from the secondary ones.

Between the grooves there are folds - convolutions, the shape of which is determined by the configuration of the grooves.

The frontal lobe is divided into the superior, middle and inferior frontal gyri. The temporal lobe contains the superior, middle and inferior temporal gyri. The anterior central gyrus (precentral) is located in front of the central sulcus. The posterior central gyrus (postcentral) is located behind the central sulcus.

In humans, there is great variability in the sulci and convolutions of the telencephalon. Despite this individual variability in the external structure of the hemispheres, this does not affect the structure of personality and consciousness.

Cytoarchitecture and myeloarchitecture of the neocortex

In accordance with the division of the hemispheres into five lobes, five main areas are distinguished - frontal, parietal, temporal, occipital and insular, which have differences in structure and perform different functions. However, the general plan of the structure of the new cortex is the same. The new crust is a layered structure (Fig. 37). I - molecular layer, formed mainly by nerve fibers running parallel to the surface. Among the parallel fibers there is a small number of granular cells. Under the molecular layer there is a second layer - the outer granular one. Layer III is the outer pyramidal layer, layer IV is the inner granular layer, layer V is the inner pyramidal layer and layer VI is multiform. The layers are named after the neurons. Accordingly, in layers II and IV, the neuron somas have a rounded shape (granular cells) (outer and internal granular layers), and in layers III and IV, the somas have a pyramidal shape (in the outer pyramidal there are small pyramids, and in the inner pyramidal layers there are large ones). pyramids or Betz cells). Layer VI is characterized by the presence of neurons of various shapes (fusiform, triangular, etc.).

The main afferent inputs to the cerebral cortex are nerve fibers coming from the thalamus. Cortical neurons that perceive afferent impulses traveling along these fibers are called sensory, and the area where sensory neurons are located is called projection zones of the cortex.

The main efferent outputs from the cortex are the axons of layer V pyramids. These are efferent, motor neurons involved in the regulation of motor functions. Most cortical neurons are intercortical, involved in information processing and providing intercortical connections.

Typical cortical neurons

Roman numerals indicate cell layers I - molecular layer; II - outer granular layer; III - outer pyramidal layer; IV - internal granular layer; V - inner primamide layer; VI-multiform layer.

a - afferent fibers; b - types of cells detected on preparations impregnated using the Goldbrzy method; c - cytoarchitecture revealed by Nissl staining. 1 - horizontal cells, 2 - Kees stripe, 3 - pyramidal cells, 4 - stellate cells, 5 - outer Bellarger stripe, 6 - inner Bellarger stripe, 7 - modified pyramidal cell.

Rice. 37. Cytoarchitecture (A) and myeloarchitecture (B) of the cerebral cortex.

While maintaining the general structural plan, it was found that different sections of the cortex (within one area) differ in the thickness of the layers. In some layers, several sublayers can be distinguished. In addition, there are differences in cellular composition (diversity of neurons, density and location). Taking into account all these differences, Brodman identified 52 areas, which he called cytoarchitectonic fields and designated in Arabic numerals from 1 to 52 (Fig. 38 A, B).

And the side view. B midsagittal; slice

Rice. 38. Field layout according to Boardman

Each cytoarchitectonic field differs not only in its cellular structure, but also in the location of the nerve fibers, which can run in both vertical and horizontal directions. The accumulation of nerve fibers within the cytoarchitectonic field is called myeloarchitectonics.

Currently, the “columnar principle” of organizing the projection zones of the cortex is becoming increasingly recognized.

According to this principle, each projection zone consists of a large number of vertically oriented columns, approximately 1 mm in diameter. Each column unites about 100 neurons, among which there are sensory, intercalary and efferent neurons, interconnected by synaptic connections. A single “cortical column” is involved in processing information from a limited number of receptors, i.e. performs a specific function.

Hemispheric fiber system

Both hemispheres have three types of fibers. Through projection fibers, excitation enters the cortex from receptors along specific pathways. Association fibers connect different areas of the same hemisphere. For example, the occipital region with the temporal region, the occipital region with the frontal region, the frontal region with the parietal region. Commissural fibers connect symmetrical areas of both hemispheres. Among the commissural fibers there are: anterior, posterior cerebral commissures and the corpus callosum (Fig. 39 A.B).

Rice. 39A. a - medial surface of the hemisphere;

b - upper-alteral surface of the hemisphere;

A - frontal pole;

B - occipital pole;

C - corpus callosum;

1 - arcuate fibers of the cerebrum connect neighboring gyri;

2 - belt - a bundle of the olfactory brain lies under the vaulted gyrus, extends from the region of the olfactory triangle to the hook;

3 - the lower longitudinal fasciculus connects the occipital and temporal regions;

4 - the superior longitudinal fasciculus connects the frontal, occipital, temporal lobes and the inferior parietal lobe;

5 - the uncinate fascicle is located at the anterior edge of the insula and connects the frontal pole with the temporal one.

Rice. 39B. Cerebral cortex in cross section. Both hemispheres are connected by bundles of white matter that form the corpus callosum (commissural fibers).

Rice. 39. Scheme of associative fibers

Reticular formation

The reticular formation (reticular substance of the brain) was described by anatomists at the end of the last century.

The reticular formation begins in the spinal cord, where it is represented by the gelatinous substance of the base of the hindbrain. Its main part is located in the central brain stem and diencephalon. It consists of neurons of various shapes and sizes, which have extensive branching processes running in different directions. Among the processes, short and long nerve fibers are distinguished. Short processes provide local connections, long ones form the ascending and descending paths of the reticular formation.

Clusters of neurons form nuclei that are located at different levels of the brain (dorsal, medulla, middle, intermediate). Most of the nuclei of the reticular formation do not have clear morphological boundaries and the neurons of these nuclei are united only by functional characteristics (respiratory, cardiovascular center, etc.). However, at the level of the medulla oblongata, nuclei with clearly defined boundaries are distinguished - the reticular giant cell, reticular parvocellular and lateral nuclei. The nuclei of the reticular formation of the pons are essentially a continuation of the nuclei of the reticular formation of the medulla oblongata. The largest of them are the caudal, medial and oral nuclei. The latter passes into the cell group of nuclei of the reticular formation of the midbrain and the reticular nucleus of the tegmentum of the brain. The cells of the reticular formation are the beginning of both ascending and descending pathways, giving numerous collaterals (endings) that form synapses on neurons of different nuclei of the central nervous system.

Fibers of reticular cells traveling to the spinal cord form the reticulospinal tract. Fibers of the ascending tracts, starting in the spinal cord, connect the reticular formation with the cerebellum, midbrain, diencephalon and cerebral cortex.

There are specific and nonspecific reticular formations. For example, some of the ascending pathways of the reticular formation receive collaterals from specific pathways (visual, auditory, etc.), along which afferent impulses are transmitted to the projection zones of the cortex.

Nonspecific ascending and descending pathways of the reticular formation affect the excitability of various parts of the brain, primarily the cerebral cortex and the spinal cord. These influences, according to their functional significance, can be both activating and inhibitory, therefore they are distinguished: 1) ascending activating influence, 2) ascending inhibitory influence, 3) descending activating influence, 4) descending inhibitory influence. Based on these factors, the reticular formation is considered as a regulating nonspecific brain system.

The most studied is the activating influence of the reticular formation on the cerebral cortex. Most of the ascending fibers of the reticular formation diffusely end in the cerebral cortex and maintain its tone and ensure attention. An example of inhibitory descending influences of the reticular formation is a decrease in the tone of human skeletal muscles during certain stages of sleep.

Neurons of the reticular formation are extremely sensitive to humoral substances. This is an indirect mechanism of influence of various humoral factors and the endocrine system on the higher parts of the brain. Consequently, the tonic effects of the reticular formation depend on the state of the whole organism (Fig. 40).

Rice. 40. The activating reticular system (ARS) is a nervous network through which sensory excitation is transmitted from the reticular formation of the brain stem to the nonspecific nuclei of the thalamus. Fibers from these nuclei regulate the level of activity of the cortex.

Subcortical nuclei

The subcortical nuclei are part of the telencephalon and are located inside the white matter of the cerebral hemispheres. These include the caudate body and putamen, collectively called the “striatum” (striatum) and the globus pallidus, consisting of the lentiform body, husk and tonsil. The subcortical nuclei and nuclei of the midbrain (red nucleus and substantia nigra) make up the system of basal ganglia (nuclei) (Fig. 41). The basal ganglia receives impulses from the motor cortex and cerebellum. In turn, signals from the basal ganglia are sent to the motor cortex, cerebellum and reticular formation, i.e. There are two neural loops: one connects the basal ganglia with the motor cortex, the other with the cerebellum.

Rice. 41. Basal ganglia system

The subcortical nuclei take part in the regulation of motor activity, regulating complex movements when walking, maintaining a posture, and when eating. They organize slow movements (stepping over obstacles, threading a needle, etc.).

There is evidence that the striatum is involved in the processes of memorizing motor programs, since irritation of this structure leads to impaired learning and memory. The striatum has an inhibitory effect on various manifestations of motor activity and on the emotional components of motor behavior, in particular on aggressive reactions.

The main transmitters of the basal ganglia are: dopamine (especially in the substantia nigra) and acetylcholine. Damage to the basal ganglia causes slow, writhing, involuntary movements accompanied by sharp muscle contractions. Involuntary jerky movements of the head and limbs. Parkinson's disease, the main symptoms of which are tremor (shaking) and muscle rigidity (a sharp increase in the tone of the extensor muscles). Due to rigidity, the patient can hardly begin to move. Constant tremor prevents small movements. Parkinson's disease occurs when the substantia nigra is damaged. Normally, the substantia nigra has an inhibitory effect on the caudate nucleus, putamen and globus pallidus. When it is destroyed, the inhibitory influences are eliminated, as a result of which the excitatory effect of the basal ganglia on the cerebral cortex and reticular formation increases, which causes the characteristic symptoms of the disease.

Limbic system

The limbic system is represented by sections of the new cortex (neocortex) and diencephalon located on the border. It unites complexes of structures of different phylogenetic ages, some of which are cortical, and some are nuclear.

The cortical structures of the limbic system include the hippocampal, parahippocampal and cingulate gyri (senile cortex). The ancient cortex is represented by the olfactory bulb and olfactory tubercles. The neocortex is part of the frontal, insular and temporal cortices.

The nuclear structures of the limbic system combine the amygdala and septal nuclei and anterior thalamic nuclei. Many anatomists consider the preoptic area of ​​the hypothalamus and the mammillary bodies to be part of the limbic system. The structures of the limbic system form 2-way connections and are connected to other parts of the brain.

The limbic system controls emotional behavior and regulates endogenous factors that provide motivation. Positive emotions are associated primarily with the excitation of adrenergic neurons, and negative emotions, as well as fear and anxiety, are associated with a lack of excitation of noradrenergic neurons.

The limbic system is involved in organizing orienting and exploratory behavior. Thus, “novelty” neurons were discovered in the hippocampus, changing their impulse activity when new stimuli appear. The hippocampus plays a significant role in maintaining the internal environment of the body and is involved in the processes of learning and memory.

Consequently, the limbic system organizes the processes of self-regulation of behavior, emotion, motivation and memory (Fig. 42).

Rice. 42. Limbic system

Autonomic nervous system

The autonomous (autonomic) nervous system provides regulation of internal organs, strengthening or weakening their activity, carries out an adaptive-trophic function, regulates the level of metabolism (metabolism) in organs and tissues (Fig. 43, 44).

1 - sympathetic trunk; 2 - cervicothoracic (stellate) node; 3 – middle cervical node; 4 - upper cervical node; 5 - internal carotid artery; 6 - celiac plexus; 7 - superior mesenteric plexus; 8 - inferior mesenteric plexus

Rice. 43. Sympathetic part of the autonomic nervous system,

III - oculomotor nerve; YII - facial nerve; IX - glossopharyngeal nerve; X - vagus nerve.

1 - ciliary node; 2 - pterygopalatine node; 3 - ear node; 4 - submandibular node; 5 - sublingual node; 6 - parasympathetic sacral nucleus; 7 - extramural pelvic node.

Rice. 44. Parasympathetic part of the autonomic nervous system.

The autonomic nervous system includes parts of both the central and peripheral nervous systems. Unlike the somatic nervous system, in the autonomic nervous system the efferent part consists of two neurons: preganglionic and postganglionic. Preganglionic neurons are located in the central nervous system. Postganglionic neurons are involved in the formation of autonomic ganglia.

The autonomic nervous system is divided into sympathetic and parasympathetic divisions.

In the sympathetic division, preganglionic neurons are located in the lateral horns of the spinal cord. The axons of these cells (preganglionic fibers) approach the sympathetic ganglia of the nervous system, located on both sides of the spine in the form of a sympathetic nerve chain.

Postganglionic neurons are located in the sympathetic ganglia. Their axons emerge as part of the spinal nerves and form synapses on the smooth muscles of internal organs, glands, vascular walls, skin and other organs.

In the parasympathetic nervous system, preganglionic neurons are located in the nuclei of the brainstem. The axons of preganglionic neurons are part of the oculomotor, facial, glossopharyngeal and vagus nerves. In addition, preganglionic neurons are also found in the sacral spinal cord. Their axons go to the rectum, bladder, and to the walls of the vessels that supply blood to the organs located in the pelvic area. Preganglionic fibers form synapses on postganglionic neurons of the parasympathetic ganglia located near or within the effector (in the latter case, the parasympathetic ganglion is called intramural).

All parts of the autonomic nervous system are subordinate to the higher parts of the central nervous system.

Functional antagonism of the sympathetic and parasympathetic nervous systems was noted, which is of great adaptive importance (see Table 1).

SECTION I V . DEVELOPMENT OF THE NERVOUS SYSTEM

The nervous system begins to develop in the 3rd week of intrauterine development from the ectoderm (outer germ layer).

On the dorsal (dorsal) side of the embryo, the ectoderm thickens. This forms the neural plate. The neural plate then bends deeper into the embryo and a neural groove is formed. The edges of the neural groove close together to form the neural tube. The long, hollow neural tube, which first lies on the surface of the ectoderm, is separated from it and plunges inward, under the ectoderm. The neural tube expands at the anterior end, from which the brain later forms. The rest of the neural tube is transformed into the brain (Fig. 45).

Rice. 45. Stages of embryogenesis of the nervous system in a transverse schematic section, a - medullary plate; b and c - medullary groove; d and e - brain tube. 1 - horny leaf (epidermis); 2 - ganglion cushion.

From cells migrating from the side walls of the neural tube, two neural crests are formed - nerve cords. Subsequently, spinal and autonomic ganglia and Schwann cells are formed from the nerve cords, which form the myelin sheaths of nerve fibers. In addition, neural crest cells participate in the formation of the pia mater and arachnoid membrane of the brain. In the inner part of the neural tube, increased cell division occurs. These cells differentiate into 2 types: neuroblasts (precursors of neurons) and spongioblasts (precursors of glial cells). Simultaneously with cell division, the head end of the neural tube is divided into three sections - the primary brain vesicles. Accordingly, they are called the forebrain (I vesicle), middle (II vesicle) and hindbrain (III vesicle). In subsequent development, the brain is divided into the telencephalon (cerebral hemispheres) and diencephalon. The midbrain is preserved as a single whole, and the hindbrain is divided into two sections, including the cerebellum with the pons and the medulla oblongata. This is the 5-vesical stage of brain development (Fig. 46, 47).

a - five brain tracts: 1 - first vesicle (end brain); 2 - second bladder (diencephalon); 3 - third bladder (midbrain); 4- fourth bladder (medulla oblongata); between the third and fourth bladder there is an isthmus; b - brain development (according to R. Sinelnikov).

Rice. 46. ​​Brain development (diagram)

A - formation of primary blisters (up to the 4th week of embryonic development). B - E - formation of secondary bubbles. B, C - end of the 4th week; G - sixth week; D - 8-9 weeks, ending with the formation of the main parts of the brain (E) - by 14 weeks.

3a - isthmus of the rhombencephalon; 7 end plate.

Stage A: 1, 2, 3 - primary brain vesicles

1 - forebrain,

2 - midbrain,

3 - hindbrain.

Stage B: the forebrain is divided into the hemispheres and basal ganglia (5) and diencephalon (6)

Stage B: The rhombencephalon (3a) is divided into the hindbrain, which includes the cerebellum (8), the pons (9) stage E and the medulla oblongata (10) stage E

Stage E: spinal cord is formed (4)

Rice. 47. The developing brain.

The formation of nerve vesicles is accompanied by the appearance of bends due to different rates of maturation of parts of the neural tube. By the 4th week of intrauterine development, the parietal and occipital curves are formed, and during the 5th week, the pontine curve is formed. By the time of birth, only the bend of the brain stem remains almost at a right angle in the area of ​​​​the junction of the midbrain and diencephalon (Fig. 48).

Lateral view illustrating curves in the midbrain (A), cervical (B), and pons (C).

1 - optic vesicle, 2 - forebrain, 3 - midbrain; 4 - hindbrain; 5 - auditory vesicle; 6 - spinal cord; 7 - diencephalon; 8 - telencephalon; 9 - rhombic lip. Roman numerals indicate the origin of the cranial nerves.

Rice. 48. The developing brain (from the 3rd to the 7th week of development).

At the beginning, the surface of the cerebral hemispheres is smooth. At 11-12 weeks of intrauterine development, the lateral sulcus (Sylvius) is formed first, then the central (Rollandian) sulcus. The laying of grooves within the lobes of the hemispheres occurs quite quickly; due to the formation of grooves and convolutions, the area of ​​the cortex increases (Fig. 49).

Rice. 49. Side view of the developing cerebral hemispheres.

A- 11th week. B- 16_ 17 weeks. B- 24-26 weeks. G- 32-34 weeks. D - newborn. The formation of the lateral fissure (5), the central sulcus (7) and other sulci and convolutions is shown.

I - telencephalon; 2 - midbrain; 3 - cerebellum; 4 - medulla oblongata; 7 - central groove; 8 - bridge; 9 - grooves of the parietal region; 10 - grooves of the occipital region;

II - furrows of the frontal region.

By migration, neuroblasts form clusters - nuclei that form the gray matter of the spinal cord, and in the brain stem - some nuclei of the cranial nerves.

Neuroblast somata have a round shape. The development of a neuron is manifested in the appearance, growth and branching of processes (Fig. 50). A small short protrusion forms on the neuron membrane at the site of the future axon - a growth cone. The axon extends and delivers nutrients to the growth cone. At the beginning of development, a neuron develops a larger number of processes compared to the final number of processes of a mature neuron. Some of the processes are retracted into the soma of the neuron, and the remaining ones grow towards other neurons with which they form synapses.

Rice. 50. Development of a spindle-shaped cell in human ontogenesis. The last two sketches show the difference in the structure of these cells in a child aged two years and an adult

In the spinal cord, axons are short in length and form intersegmental connections. Longer projection fibers form later. Somewhat later than the axon, dendritic growth begins. All branches of each dendrite are formed from one trunk. The number of branches and length of dendrites is not completed in the prenatal period.

The increase in brain mass during the prenatal period occurs mainly due to an increase in the number of neurons and the number of glial cells.

The development of the cortex is associated with the formation of cellular layers (in the cerebellar cortex there are three layers, and in the cerebral cortex there are six layers).

The so-called glial cells play an important role in the formation of the cortical layers. These cells take a radial position and form two vertically oriented long processes. Neuronal migration occurs along the processes of these radial glial cells. The more superficial layers of the bark are formed first. Glial cells also take part in the formation of the myelin sheath. Sometimes one glial cell participates in the formation of the myelin sheaths of several axons.

Table 2 reflects the main stages of development of the nervous system of the embryo and fetus.

Table 2.

The main stages of development of the nervous system in the prenatal period.

Thus, the development of the brain in the prenatal period occurs continuously and in parallel, but is characterized by heterochrony: the rate of growth and development of phylogenetically older formations is greater than that of phylogenetically younger formations.

Genetic factors play a leading role in the growth and development of the nervous system during the prenatal period. The average weight of a newborn's brain is approximately 350 g.

Morpho-functional maturation of the nervous system continues in the postnatal period. By the end of the first year of life, the weight of the brain reaches 1000 g, while in an adult the brain weight is on average 1400 g. Consequently, the main increase in brain weight occurs in the first year of a child’s life.

The increase in brain mass in the postnatal period occurs mainly due to an increase in the number of glial cells. The number of neurons does not increase, since they lose the ability to divide already in the prenatal period. The overall density of neurons (the number of cells per unit volume) decreases due to the growth of the soma and processes. The number of branches of dendrites increases.

In the postnatal period, myelination of nerve fibers also continues both in the central nervous system and the nerve fibers that make up the peripheral nerves (cranial and spinal).

The growth of spinal nerves is associated with the development of the musculoskeletal system and the formation of neuromuscular synapses, and the growth of cranial nerves with the maturation of sensory organs.

Thus, if in the prenatal period the development of the nervous system occurs under the control of the genotype and is practically independent of the influence of the external environment, then in the postnatal period external stimuli play an increasingly important role. Irritation of the receptors causes afferent impulse flows that stimulate the morpho-functional maturation of the brain.

Under the influence of afferent impulses, spines are formed on the dendrites of cortical neurons - outgrowths that are special postsynaptic membranes. The more spines, the more synapses and the more involved the neuron is in information processing.

Throughout postnatal ontogenesis up to puberty, as well as in the prenatal period, brain development occurs heterochronously. Thus, the final maturation of the spinal cord occurs earlier than the brain. The development of stem and subcortical structures, earlier than the cortical ones, the growth and development of excitatory neurons overtakes the growth and development of inhibitory neurons. These are general biological patterns of growth and development of the nervous system.

Morphological maturation of the nervous system correlates with the characteristics of its functioning at each stage of ontogenesis. Thus, earlier differentiation of excitatory neurons compared to inhibitory neurons ensures the predominance of flexor muscle tone over extensor tone. The arms and legs of the fetus are in a bent position - this determines a position that provides minimal volume, due to which the fetus takes up less space in the uterus.

Improving the coordination of movements associated with the formation of nerve fibers occurs throughout the preschool and school periods, which is manifested in the consistent development of sitting, standing, walking, writing, etc. postures.

The increase in the speed of movements is caused mainly by the processes of myelination of peripheral nerve fibers and an increase in the speed of excitation of nerve impulses.

The earlier maturation of subcortical structures compared to cortical ones, many of which are part of the limbic structure, determines the characteristics of the emotional development of children (greater intensity of emotions and the inability to restrain them are associated with the immaturity of the cortex and its weak inhibitory influence).

In old age and senility, anatomical and histological changes in the brain occur. Atrophy of the cortex of the frontal and superior parietal lobes often occurs. The fissures become wider, the ventricles of the brain enlarge, and the volume of white matter decreases. Thickening of the meninges occurs.

With age, neurons decrease in size, but the number of nuclei in cells may increase. In neurons, the content of RNA necessary for the synthesis of proteins and enzymes also decreases. This impairs the trophic functions of neurons. It has been suggested that such neurons fatigue more quickly.

In old age, the blood supply to the brain is also disrupted, the walls of blood vessels thicken and cholesterol plaques are deposited on them (atherosclerosis). It also impairs the functioning of the nervous system.

LITERATURE

Atlas “Human Nervous System”. Comp. V.M. Astashev. M., 1997.

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Borzyak E.I., Bocharov V.Ya., Sapina M.R. Human anatomy. - M.: Medicine, 1993. T.2. 2nd ed., revised. and additional

Zagorskaya V.N., Popova N.P. Anatomy of the nervous system. Course program. MOSU, M., 1995.

Kishsh-Sentagotai. Anatomical atlas of the human body. - Budapest, 1972. 45th edition. T. 3.

Kurepina M.M., Vokken G.G. Human anatomy. - M.: Education, 1997. Atlas. 2nd edition.

Krylova N.V., Iskrenko I.A. Brain and pathways (Human anatomy in diagrams and drawings). M.: Publishing house of the Russian Peoples' Friendship University, 1998.

Brain. Per. from English Ed. Simonova P.V. - M.: Mir, 1982.

Human morphology. Ed. B.A. Nikityuk, V.P. Chtetsova. - M.: Moscow State University Publishing House, 1990. P. 252-290.

Prives M.G., Lysenkov N.K., Bushkovich V.I. Human anatomy. - L.: Medicine, 1968. P. 573-731.

Savelyev S.V. Stereoscopic atlas of the human brain. M., 1996.

Sapin M.R., Bilich G.L. Human anatomy. - M.: Higher School, 1989.

Sinelnikov R.D. Atlas of human anatomy. - M.: Medicine, 1996. 6th ed. T. 4.

Schade J., Ford D. Fundamentals of Neurology. - M.: Mir, 1982.

Tissue is a collection of cells and intercellular substance that are similar in structure, origin and functions.

Some anatomists do not include the medulla oblongata in the hindbrain, but distinguish it as an independent section.

The central nervous system (CNS) is the main part of the nervous system in humans and animals, which consists of a cluster of neurons (nerve cells) and their processes. It is represented in humans and vertebrates by the brain and spinal cord. In invertebrates, it is a system of closely connected nerve ganglia. The main task and function of the central nervous system is the implementation of complex and simple reflexes.

Divisions of the central nervous system

The nervous system of humans and higher animals consists of the following sections:

1. Spinal cord;
2. Medulla;
3. Midbrain;
4. Diencephalon;
5. Cerebellum.

All these departments regulate the activity of systems in a highly developed organism and individual organs. They also connect them and carry out their interaction. Ensure the integrity of activity and the unity of the body.

The higher departments of the central nervous system are:

1. Cortex of the cerebral hemispheres;
2. Subcortical nearby formations.

They regulate the relationship and connection between the environment and the organism as a whole.

Functions of the central nervous system

Among the main functions of the central nervous system are the following:

Methods for studying the central nervous system and its functions

All research methods are associated with the intensive development of the physiology of the central nervous system. They are divided into the following types:

Reflexes

Reflex is a response of the body to any action of a stimulus, which is carried out with the participation of the central nervous system. When translated from Latin, this term means “display.” This term was discovered by the scientist R. Descartes in order to characterize the body's reaction to respond to irritation of the senses.

Reflexes are classified into the following subtypes depending on their type:

Properties of the centers of the nervous system

Nerve center is called a union of neurons that will take part in the work of one specific reflex of the body. Throughout the body, in order to form an adaptive complex process, a functional reconnection of neurons is carried out, which are located at different levels of the central nervous system.

Nerve centers have a number of features and properties. These include:

1. Excitation is one-sided - to the working organ from the receptor.
2. In nerve centers, excitation manifests itself more slowly than along nerve fibers.
3. The summation of excitations also occurs in the nerve centers. It can be sequential, simultaneous or temporary.
4. Transformation to the rhythm of excitement. It is a change in the number of impulses that leave the nerve centers compared to the number that leads to it. May manifest itself in an increase or decrease in the number of impulses.
5. The aftereffect of reflexes is the cessation of the reaction a little later compared to the action of the pathogen.
6. Increased sensitivity to substances of chemical origin and oxygen deficiency.
7. Nerve centers get tired quickly and have a low level of locality, and are easily inhibited.
8. Nerve centers have a plastic structure - they can change their functional purpose and partially restore functions that have been lost.

Principles in Central Nervous System Coordination

The basis of the coordination activity of the nervous system is the interaction of the processes of inhibition and excitation. There are a number of principles that ensure coordination interaction.