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:

Solid. This is the outer shell. It is located in the internal cavity of the skull and spinal canal.
Arachnoid. This cover is located under the hard part. In its structure it has nerves and blood vessels.
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

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.
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.
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.
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.
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.

1. Structure of the telencephalon.

Surfaces of the cerebral hemispheres.

Cortex.

Basal ganglia and white matter terminal

2. Structure of the diencephalon.

Hypothalamus.

III ventricle.

3. The main pathways of the brain.

Ascending afferent pathways.

Descending efferent pathways.

1. Structure of the telencephalon.

Finite brain(telencephalon) consists of two cerebral hemispheres, separated from each other by a longitudinal fissure. In the depths of the gap there is a connection connecting them corpus callosum. In addition to the corpus callosum, the hemispheres also connect front, back spikes And vault commissure. Each hemisphere has three poles: frontal, occipital and temporal. Three edges (superior, inferior and medial) divide the hemispheres into three surfaces: superolateral, medial and inferior. Each hemisphere is divided into lobes. Central sulcus(Rolandova) separates the frontal lobe from the parietal lobe, lateral groove(Sylvian) temporal from the frontal and parietal, the parieto-occipital fissure separates the parietal and occipital lobes. The insular lobe is located deep in the lateral sulcus. Smaller grooves divide the lobes into convolutions.

Superolateral surface of the cerebral hemisphere. Frontal lobe, located in the anterior section of each hemisphere of the cerebrum, is limited below by the lateral (Sylvian) fissure, and behind by the deep central groove (Rolandic), located in the frontal plane. Anterior to the central sulcus, almost parallel to it, is located precentral sulcus. From the precentral sulcus forward, almost parallel to each other, they are directed top And inferior frontal sulcus, which divide the superolateral surface of the frontal lobe from the gyrus. Between the central sulcus posteriorly and the precentral sulcus anteriorly there is precentral gyrus. Lying above the superior frontal sulcus superior frontal gyrus occupies the upper part of the frontal lobe.

Between the superior and inferior frontal sulci passes middle frontal gyrus. Located inferior to the inferior frontal sulcus inferior frontal gyrus, into which they protrude from behind ascending And anterior branch of the lateral sulcus, dividing the lower part of the frontal lobe into small convolutions. Tegmental part (frontal operculum), located between the ascending branch and the lower part of the lateral sulcus, covers the insular lobe, which lies deep in the sulcus. Orbital part lies inferiorly from the anterior branch, continuing to the inferior surface of the frontal lobe. At this point, the lateral groove widens, turning into lateral fossa cerebrum .

Parietal lobe, located posterior to the central sulcus, separated from the occipital parieto-occipital sulcus, which is located on the medial surface of the hemisphere, protruding deeply into its upper edge. The parieto-occipital groove passes to the lateral surface, where the border between the parietal and occipital lobes is a conventional line - the continuation of this groove downwards. The inferior border of the parietal lobe is the posterior branch of the lateral sulcus, separating it from the temporal lobe. Postcentral sulcus runs behind the central sulcus, almost parallel to it.

Between the central and postcentral sulci is located postcentral gyrus, which at the top passes to the medial surface of the cerebral hemisphere, where it connects with the precentral gyrus of the frontal lobe, forming with it precentral lobule. On the superior lateral surface of the hemisphere below, the postcentral gyrus also passes into the precentral gyrus, covering the central sulcus from below. It extends posteriorly from the postcentral sulcus intraparietal sulcus, parallel to the upper edge of the hemisphere. Above the intraparietal sulcus there is a group of small convolutions called superior parietal lobule; located below inferior parietal lobule.

The smallest occipital lobe located behind parieto-occipital sulcus and its conditional continuation on the superolateral surface of the hemisphere. The occipital lobe is divided into several convolutions by grooves, of which the most constant is transverse occipital sulcus .

Temporal lobe, occupying the inferolateral parts of the hemisphere, is separated from the frontal and parietal lobes by the lateral sulcus. The insular lobe is covered by the edge of the temporal lobe. On the lateral surface of the temporal lobe, almost parallel to the lateral sulcus, runs top And inferior temporal gyrus. On the upper surface of the superior temporal gyrus, several weakly defined transverse gyri are visible ( Heschl's convolutions). Between the superior and inferior temporal grooves are located middle temporal gyrus. Below the inferior temporal sulcus is inferior temporal gyrus .

Insula (islet) located in the depths of the lateral sulcus, covered by a tegmentum formed by parts of the frontal, parietal and temporal lobes. Deep circular groove of the insula separates the insula from the surrounding parts of the brain. The inferoanterior part of the insula is devoid of grooves and has a slight thickening - threshold of the island. On the surface of the islet there is long And short convolutions.

Medial surface of the cerebral hemisphere. All of its lobes, except the insular lobe, take part in the formation of the medial surface of the cerebral hemisphere. Sulcus of the corpus callosum goes around it from above, separating the corpus callosum from lumbar gyrus, goes down and forward and continues in hippocampal sulcus .

Passes over the cingulate gyrus cingulate groove, which begins anteriorly and inferiorly from the beak of the corpus callosum. As it rises, the groove turns back and runs parallel to the groove of the corpus callosum. At the level of its ridge, its marginal part extends upward from the cingulate sulcus, and the sulcus itself continues into the subparietal sulcus. The marginal part of the cingulate groove posteriorly limits pericentral lobule, and in front - precuneus, which belongs to the parietal lobe. Inferiorly and posteriorly through the isthmus, the cingulate gyrus passes into parahippocampal gyrus which ends in front crochet and bounded from above hippocampal sulcus . Cingulate gyrus, isthmus And parahippocampal gyrus united under the name vaulted gyrus. Located deep in the hippocampal sulcus dentate gyrus. At the level of the splenium of the corpus callosum, it branches upward from the cingulate sulcus marginal part of the cingulate groove .

Inferior surface of the cerebral hemisphere has the most difficult terrain. In front is the surface of the frontal lobe, behind it is the temporal pole and the lower surface of the temporal and occipital lobes, between which there are no clear boundaries. Between longitudinal slot hemispheres and olfactory sulcus frontal lobe is located gyrus rectus. Lateral to the olfactory sulcus lie orbital gyri . Lingual gyrus the occipital lobe on the lateral side is limited by the occipitotemporal (collateral) groove. This groove passes to the inferior surface of the temporal lobe, dividing parahippocampal And medial occipitotemporal gyrus. Anterior to the occipitotemporal sulcus is nasal groove, limiting the anterior end of the parahippocampal gyrus - hook. Occipitotemporal sulcus divides medial And lateral occipitotemporal gyrus.

Cortex , cortex cerebri, is the most highly differentiated part of the nervous system.

The cerebral cortex consists of a huge number of cells, which, according to their morphological characteristics, can be divided into six layers:

1. outer zonal, or molecular layer, lamina zonalis ;

2. outer granular layer, lamina granularis externa ;

3. pyramidal layer, lamina pyramidalis ;

4. inner granular layer, lamina granularis interna ;

5. ganglion layer, lamina ganglionaris ;

6. polymorphic layer, lamina multiformis .

The structure of each of these layers of the cortex in different parts of the brain has its own characteristics, expressed in a change in the number of layers, in different numbers, sizes, topography and structure of the nerve cells that form it.

Based on a subtle study of various parts of the cerebral cortex, a large number of fields have now been described in it (see Fig.), each of which is characterized by the individual characteristics of its architectonics, which made it possible to create a map of the fields of the cerebral cortex (cytoarchitectonics), as well as to establish the features distribution of cortical fibers (myeloarchitecture).

Cortical sections Each analyzer in the cerebral cortex has certain areas where their nuclei are localized, and, in addition, separate groups of nerve cells located outside these areas. The nuclei of the motor analyzer are localized in the circumcentral gyrus, precentral gyrus, and the posterior part of the middle and inferior frontal gyri.

In the upper section In the precentral gyrus and pericentral lobule, the cortical sections of the motor analyzers of the muscles of the lower limb are localized; below are areas related to the muscles of the pelvis, abdominal wall, trunk, upper limbs, neck and, finally, in the lowest section - the head.

In the posterior region middle frontal gyrus The cortical section of the motor analyzer for combined rotation of the head and eyes is localized. There is also a motor analyzer of written speech, which is related to voluntary movements associated with writing letters, numbers and other characters.

Posterior part of the inferior frontal gyrus is the location of the motor speech analyzer.

Cortical section of the olfactory analyzer(and taste) is in the hook; visual - occupies the edges of the sulcus of the bird's spur, auditory - in the middle part of the superior temporal gyrus, and as far as posterior, in the posterior part of the superior temporal gyrus - the auditory analyzer of speech signals (control of one's own speech and perception of someone else's).

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Rice. 8.19 Spinal cord at the midcervical level. The main tracts of the white matter of the spinal cord are shown.

Spinal cord is part of the central nervous system and consists of ascending and descending tracts that transmit information between the brain and the PNS. The tracts are connected at various levels by short interneurons, which allow for increased integration and control of motor function and sensitivity at the spinal level (Fig. 8.19).

Rice. 8.20 Medulla oblongata, pons and midbrain, (a) The medulla oblongata is the first part of the brain stem in which motor fibers and some sensory fibers intersect, (b) The pons lies between the spinal cord and the midbrain. It can be considered as a relay station between the cerebellum, cerebrum and peripheral nervous system, (c) The superior colliculus of the midbrain allows monitoring of visual stimuli. (d) The inferior colliculus of the midbrain provides selective perception of auditory stimuli.

Medulla directly connected to the spinal cord and is its continuation and the first part of the brain stem (Fig. 8.20a). The medulla oblongata contains nuclei for cranial nerves V, IX, X, XI and XII, where motor fibers and some sensory fibers intersect.

Between the medulla oblongata and the midbrain is located bridge. It can be considered as a relay station between the cerebellum, cerebrum and PNS. The pons contains nuclei for cranial nerves V, VI, VII, and VIII and motor nuclei in the pons reticular formation, which are involved in postural, cardiovascular, and respiratory control (see Fig. 8.206).

Rice. 8.21 Lateral view of the brain.

Cerebellum located behind the pons (Fig. 8.21) and has incoming and outgoing connections with the sensory and motor tracts ascending and descending from the spinal cord. It is the largest motor structure in the brain. Although the function of the cerebellum is not completely understood, its diversity of connections allows the cerebellum to control movement and act as a center for integrating sensory and motor information to perform complex tasks.

Above the bridge is midbrain. This is the most primitive part of the human brain. The midbrain terminates in two huge bundles of fibers that form the cerebral peduncles, carrying fibers to and from the thalamus and hemispheres. The midbrain also contains the superior (visual) and inferior (auditory) colliculi (see Fig. 8.20c, 8.20d), nuclei for cranial nerves III and IV pairs, two motor nuclei, the red nucleus and the substantia nigra, which connects and acts as a relay between the main ganglion and the motor system (see Fig. 8.20c).

Rice. 8.22 Diencephalon. Consists of the hypothalamus, subthalamus, epithalamus and thalamus.

Diencephalon- central nucleus of the brain - consists of the hypothalamus, subthalamus, epithalamus and thalamus (Fig. 8.22):

The hypothalamus contributes to many homeostatic functions, such as regulating the ANS and the endocrine system through the pituitary gland. It also plays a role in controlling the basic instincts: hunger, thirst, fatigue, self-preservation and sexual desire;

the subthalamus is involved in motor function and is connected with the basal ganglia, red nuclei and substantia nigra;

The epithalamus consists of the leash and the pineal gland (epiphysis). The leash ganglion is the center for the integration of olfactory, visceral and somatic centripetal pathways associated with the reticular formation. The function of the pineal gland is unclear, but it is known to contain high concentrations of melatonin and 5-hydroxytryptophan, which may play a role in regulating circadian rhythms;

The thalamus is the largest part of the midbrain. Functionally and anatomically, the thalamus is closely connected with the cerebral cortex. Almost all fibers going to the cerebral hemispheres pass through a synapse within the thalamus. It has outgoing connections to virtually every part of the brain. The function of the thalamus is probably to integrate incoming sensory information through the nuclei associated with it. The information is then sent to the cerebral cortex for interpretation.

Rice. 8.23 Basal ganglia. Bilateral masses of gray matter form deep structures. The striatum consists of the caudate nucleus and the lenticular nucleus, which are separated by an internal capsule, with the exception of the lower part of the caudate nucleus, the head of which is continuously connected with the putamen of the lenticular nucleus. The lentiform nucleus consists of the putamen and the globus pallidus.

Basal ganglia- a collective term given to the bilateral masses of deep gray matter (Fig. 8.23). The basal ganglia have centripetal and efferent connections with the cerebral cortex, thalamus, subthalamus, and brainstem and control motor function through the cerebral hemispheres.

The hemispheres of the brain form telencephalon. Consciousness, the ability to adapt and respond to changing circumstances, to think abstractly, to learn, to generate hypotheses, and to benefit not only from one’s own experience are determined by the complexity and size of the hemispheres. This higher functioning leads to the development of a rich emotional life, so the risk of profound mental illness is high.

Certain functions are more associated with certain areas of the cerebral hemispheres

Cerebral hemispheres divided into frontal, temporal, parietal and occipital lobes (see Fig. 8.21).

The exact localization of any specific function within the brain is unknown, perhaps because no individual function is localized exclusively to one specific region. However, as with the lower parts of the central nervous system, individual functions are more associated with certain areas:

precentral gyrus of the frontal lobe - with voluntary motor function;

postcentral gyrus of the parietal lobe - with sensory function;

part of the dominant frontal lobe is thought to play a primary role in the development and use of language;

parts of the frontal lobes on both sides are probably involved in the formation of personality, logic and intelligence;

the temporal lobes provide a greater proportion of the functions of memory, integration, and auditory centers;

The parietal lobes likely provide complex integrative function for sensory, motor, and, to a lesser extent, emotional functioning. They also enable the planning and initiation of complex actions and play a critical role in topographical, object and verbal recognition and their association with emotion;

The occipital cortex receives and processes visual information.

The limbic system is critical in the formation of memory and emotions

Limbic system- a set of related structures, including a variety of deep structures (for example, the amygdala), selected areas of the cerebral cortex (for example, the zonule) and segments of other structures (for example, the hypothalamus) (Table 8.9; Fig. 8.24). The main component of the limbic system is the circuit. Through this loop, the hippocampus transmits information through the fornix to the papillary bodies of the hypothalamus, which carry it to the anterior nucleus of the thalamus through the mamillothalamic tracts. It is then sent through the internal capsule back to the hippocampus. The exact functions of the limbic system remain unclear, but damage to certain parts of various loops leads to:

Amygdala (basolateral complex, centromedial complex, parts of stria terminalis and hypothalamus)

Caudate nuclei

Mamillary bodies

Anterior and dorsomedial nuclei of the thalamus (some include other cortical areas: orbitofrontal area, temporal fields and insula)

Symptoms of hallucinations and delusions in psychiatric patients may result from dysfunction of the limbic system.

The reticular formation has a nonspecific alerting signaling function and contributes to motor, sensory (pain) and autonomic functions

Reticular formation- a network of neurons with scattered dendritic connections that occupies the middle of the brain stem and extends upward from the substance intermedia to the spinal cord to the intralaminar nuclei of the thalamus. It is loosely organized into three longitudinal nuclear columns (medial, middle and lateral), each of which is subdivided into three ventrocaudal ones (mesencephalic, varolian and medullary).

The reticular formation has input from ascending sensory neurons, the cerebellum, basal ganglia, hypothalamus and cortex and outputs to the hypothalamus, thalamus and spinal cord.

The nonspecific alerting function of the reticular formation may be related to the ascending reticulothalamocortical pathways (ascending reticular activating system). The reticular formation also contributes to motor, sensory (pain) and autonomic functions, particularly affecting breathing and vasomotor function.

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.

Rice. 12. Spinal cord.

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 tender 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).

1-thin core;

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 pons 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 - nuclius paraventricularis; 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 the secretion of milk.

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.

*Fetal age (weeks)*	*Nervous system development*
2,5	A neural groove is outlined
3.5	The neural tube and nerve cords are formed
4	3 brain bubbles are formed; nerves and ganglia form
5	5 brain bubbles form
6	The meninges are outlined
7	The hemispheres of the brain reach a large size
8	Typical neurons appear in the cortex
10	The internal structure of the spinal cord is formed
12	General structural features of the brain are formed; differentiation of neuroglial cells begins
16	Distinct lobes of the brain
20-40	Myelination of the spinal cord begins (week 20), layers of the cortex appear (25 weeks), grooves and convolutions form (28-30 weeks), myelination of the brain begins (36-40 weeks)

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.

Blum F., Leiserson A., Hofstadter L. Brain, mind and behavior. M.: Mir, 1988.

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.

Nerve endings are located throughout the human body. They have a vital function and are an integral part of the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.

The physiology of the nervous system is a complex composite structure.

The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers that are excited when exposed and transmit impulses. The impulses reach the centers where they are analyzed. Having analyzed the received signal, the brain transmits the necessary reaction to the stimulus to the appropriate organs or parts of the body. The human nervous system is briefly described by the following functions:

providing reflexes;
regulation of internal organs;
ensuring the interaction of the body with the external environment, by adapting the body to changing external conditions and stimuli;
interaction of all organs.

The importance of the nervous system lies in ensuring the vital functions of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.

Structure of the central nervous system

The anatomy of the central nervous system (CNS) is a collection of neuronal cells and neural processes of the spinal cord and brain. A neuron is a unit of the nervous system.

The function of the central nervous system is to ensure reflex activity and process impulses coming from the PNS.

The anatomy of the central nervous system, the main unit of which is the brain, is a complex structure of branched fibers.

The higher nerve centers are concentrated in the cerebral hemispheres. This is a person’s consciousness, his personality, his intellectual abilities and speech. The main function of the cerebellum is to ensure coordination of movements. The brain stem is inextricably linked with the hemispheres and cerebellum. This section contains the main nodes of the motor and sensory pathways, which ensures such vital functions of the body as regulating blood circulation and ensuring respiration. The spinal cord is the distribution structure of the central nervous system; it provides branching of the fibers that form the PNS.

The spinal ganglion is the site of concentration of sensory cells. With the help of the spinal ganglion, the activity of the autonomic department of the peripheral nervous system is carried out. Ganglia or nerve ganglia in the human nervous system are classified as the PNS; they perform the function of analyzers. Ganglia do not belong to the human central nervous system.

Features of the structure of the PNS

Thanks to the PNS, the activity of the entire human body is regulated. The PNS consists of cranial and spinal neurons and fibers that form ganglia.

The human peripheral nervous system has a very complex structure and functions, so any slightest damage, for example, damage to blood vessels in the legs, can cause serious disruptions to its functioning. Thanks to the PNS, all parts of the body are controlled and the vital functions of all organs are ensured. The importance of this nervous system for the body cannot be overestimated.

The PNS is divided into two divisions - the somatic and autonomic PNS systems.

The somatic nervous system performs double duty - collecting information from the sensory organs, and further transmitting this data to the central nervous system, as well as ensuring the motor activity of the body by transmitting impulses from the central nervous system to the muscles. Thus, it is the somatic nervous system that is the instrument of human interaction with the outside world, as it processes signals received from the organs of vision, hearing and taste buds.

The autonomic nervous system ensures the functions of all organs. It controls the heartbeat, blood supply, and breathing. It contains only motor nerves that regulate muscle contraction.

To ensure the heartbeat and blood supply, the efforts of the person himself are not required - this is controlled by the autonomic part of the PNS. The principles of the structure and function of the PNS are studied in neurology.

Departments of the PNS

The PNS also consists of the afferent nervous system and the efferent nervous system.

The afferent region is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to any impact.

The efferent system differs in that it processes impulses transmitted from the brain to effectors, that is, muscles and glands.

One of the important parts of the autonomic division of the PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system controls the motility of the small and large intestines. This section also regulates the secretions released in the gastrointestinal tract and provides local blood supply.

The importance of the nervous system is to ensure the functioning of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The child’s central nervous system develops not only during the prenatal period, but also during the first year of life. Ontogenesis of the nervous system begins from the first week after conception.

The basis for brain development is formed already in the third week after conception. The main functional nodes are identified by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher parts of the brain are already better developed than the spinal part.

By the time a baby is born, the brain is the most developed. The size of the brain in a newborn is approximately an eighth of the child’s weight and ranges from 400 g.

The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may include an abundance of new irritating factors for the baby. This is how the plasticity of the nervous system manifests itself, that is, the ability of this structure to be rebuilt. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.

Types of CNS

In the centers located in the cerebral cortex, two processes simultaneously interact - inhibition and excitation. The rate at which these states change determines the types of nervous system. While one part of the central nervous system is excited, another is slowed down. This determines the features of intellectual activity, such as attention, memory, concentration.

Types of the nervous system describe the differences between the speed of inhibition and excitation of the central nervous system in different people.

People may differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the process of inhibition to the process of excitation, and vice versa.

The types of nervous system are divided into four types.

The weak type, or melancholic, is considered the most predisposed to the occurrence of neurological and psycho-emotional disorders. It is characterized by slow processes of excitation and inhibition. The strong and unbalanced type is choleric. This type is distinguished by the predominance of excitation processes over inhibition processes.
Strong and agile - this is a type of sanguine person. All processes occurring in the cerebral cortex are strong and active. A strong but inert, or phlegmatic type, is characterized by a low speed of switching nervous processes.

The types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes the physiological characteristics of the processes occurring in the central nervous system.

CNS protection

The anatomy of the nervous system is very complex. The central nervous system and PNS suffer due to the effects of stress, overexertion and lack of nutrition. For the normal functioning of the central nervous system, vitamins, amino acids and minerals are necessary. Amino acids take part in brain function and are building materials for neurons. Having figured out why vitamins and amino acids are needed and why, it becomes clear how important it is to provide the body with the necessary amount of these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The regimen for taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.

Damage to bundles of nerve fibers, congenital pathologies and abnormalities of brain development, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases - immobility, paresis, muscle atrophy, encephalitis and much more.

Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If an oncological disease of the central nervous system is suspected, an analysis is prescribed - histology of the affected parts, that is, an examination of the composition of the tissue. A neuron, as part of a cell, can also mutate. Such mutations can be identified by histology. Histological analysis is carried out according to the doctor’s indications and consists of collecting the affected tissue and its further study. For benign formations, histology is also performed.

The human body contains many nerve endings, damage to which can cause a number of problems. Damage often leads to impaired mobility of a body part. For example, an injury to the hand can lead to pain in the fingers and impaired movement. Osteochondrosis of the spine can cause pain in the foot due to the fact that an irritated or compressed nerve sends pain impulses to receptors. If the foot hurts, people often look for the cause in a long walk or injury, but the pain syndrome can be triggered by damage to the spine.

If you suspect damage to the PNS, as well as any related problems, you should be examined by a specialist.