Central nervous system (CNS). Human central nervous system: structure and main functions Human central nervous system

With the evolutionary complication of multicellular organisms, the functional specialization of cells, the need arose for the regulation and coordination of life processes at the supracellular, tissue, organ, systemic and organismal levels. These new regulatory mechanisms and systems should have appeared along with the preservation and complication of the mechanisms for regulating the functions of individual cells with the help of signaling molecules. Adaptation of multicellular organisms to changes in the environment of existence could be carried out on the condition that new regulatory mechanisms would be able to provide fast, adequate, targeted responses. These mechanisms must be able to memorize and retrieve from the memory apparatus information about previous effects on the body, as well as have other properties that ensure effective adaptive activity of the body. They were the mechanisms of the nervous system that appeared in complex, highly organized organisms.

Nervous system is a set of special structures that unites and coordinates the activity of all organs and systems of the body in constant interaction with the external environment.

The central nervous system includes the brain and spinal cord. The brain is subdivided into the hindbrain (and the pons), the reticular formation, subcortical nuclei,. The bodies form the gray matter of the CNS, and their processes (axons and dendrites) form the white matter.

General characteristics of the nervous system

One of the functions of the nervous system is perception various signals (stimuli) of the external and internal environment of the body. Recall that any cells can perceive various signals of the environment of existence with the help of specialized cellular receptors. However, they are not adapted to the perception of a number of vital signals and cannot instantly transmit information to other cells that perform the function of regulators of integral adequate reactions of the body to the action of stimuli.

The impact of stimuli is perceived by specialized sensory receptors. Examples of such stimuli can be light quanta, sounds, heat, cold, mechanical influences (gravity, pressure change, vibration, acceleration, compression, stretching), as well as signals of a complex nature (color, complex sounds, words).

To assess the biological significance of the perceived signals and organize an adequate response to them in the receptors of the nervous system, their transformation is carried out - coding into a universal form of signals understandable to the nervous system - into nerve impulses, holding (transferred) which along the nerve fibers and pathways to the nerve centers are necessary for their analysis.

The signals and the results of their analysis are used by the nervous system to response organization to changes in the external or internal environment, regulation and coordination functions of cells and supracellular structures of the body. Such responses are carried out by effector organs. The most common variants of responses to influences are motor (motor) reactions of skeletal or smooth muscles, changes in the secretion of epithelial (exocrine, endocrine) cells initiated by the nervous system. Taking a direct part in the formation of responses to changes in the environment of existence, the nervous system performs the functions homeostasis regulation, ensure functional interaction organs and tissues and their integration into a single whole body.

Thanks to the nervous system, an adequate interaction of the organism with the environment is carried out not only through the organization of responses by effector systems, but also through its own mental reactions - emotions, motivations, consciousness, thinking, memory, higher cognitive and creative processes.

The nervous system is divided into central (brain and spinal cord) and peripheral - nerve cells and fibers outside the cranial cavity and spinal canal. The human brain contains over 100 billion nerve cells. (neurons). Accumulations of nerve cells that perform or control the same functions form in the central nervous system nerve centers. The structures of the brain, represented by the bodies of neurons, form the gray matter of the CNS, and the processes of these cells, uniting into pathways, form the white matter. In addition, the structural part of the CNS is glial cells that form neuroglia. The number of glial cells is about 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

According to the features of the functions performed and the structure, the nervous system is divided into somatic and autonomous (vegetative). Somatic structures include the structures of the nervous system, which provide the perception of sensory signals mainly from the external environment through the sense organs, and control the work of the striated (skeletal) muscles. The autonomic (vegetative) nervous system includes structures that provide the perception of signals mainly from the internal environment of the body, regulate the work of the heart, other internal organs, smooth muscles, exocrine and part of the endocrine glands.

In the central nervous system, it is customary to distinguish structures located at different levels, which are characterized by specific functions and a role in the regulation of life processes. Among them, the basal nuclei, brain stem structures, spinal cord, peripheral nervous system.

The structure of the nervous system

The nervous system is divided into central and peripheral. The central nervous system (CNS) includes the brain and spinal cord, and the peripheral nervous system includes the nerves extending from the central nervous system to various organs.

Rice. 1. The structure of the nervous system

Rice. 2. Functional division of the nervous system

Significance of the nervous system:

• unites the organs and systems of the body into a single whole;
• regulates the work of all organs and systems of the body;
• carries out the connection of the organism with the external environment and its adaptation to environmental conditions;
• forms the material basis of mental activity: speech, thinking, social behavior.

Structure of the nervous system

The structural and physiological unit of the nervous system is - (Fig. 3). It consists of a body (soma), processes (dendrites) and an axon. Dendrites strongly branch and form many synapses with other cells, which determines their leading role in the perception of information by the neuron. The axon starts from the cell body with the axon mound, which is the generator of a nerve impulse, which is then carried along the axon to other cells. The axon membrane in the synapse contains specific receptors that can respond to various mediators or neuromodulators. Therefore, the process of mediator release by presynaptic endings can be influenced by other neurons. Also, the membrane of the endings contains a large number of calcium channels through which calcium ions enter the ending when it is excited and activate the release of the mediator.

Rice. 3. Scheme of a neuron (according to I.F. Ivanov): a - structure of a neuron: 7 - body (pericaryon); 2 - core; 3 - dendrites; 4.6 - neurites; 5.8 - myelin sheath; 7- collateral; 9 - node interception; 10 — a kernel of a lemmocyte; 11 - nerve endings; b — types of nerve cells: I — unipolar; II - multipolar; III - bipolar; 1 - neuritis; 2 - dendrite

Usually, in neurons, the action potential occurs in the region of the axon hillock membrane, the excitability of which is 2 times higher than the excitability of other areas. From here, the excitation spreads along the axon and the cell body.

Axons, in addition to the function of conducting excitation, serve as channels for the transport of various substances. Proteins and mediators synthesized in the cell body, organelles and other substances can move along the axon to its end. This movement of substances is called axon transport. There are two types of it - fast and slow axon transport.

Each neuron in the central nervous system performs three physiological roles: it receives nerve impulses from receptors or other neurons; generates its own impulses; conducts excitation to another neuron or organ.

According to their functional significance, neurons are divided into three groups: sensitive (sensory, receptor); intercalary (associative); motor (effector, motor).

In addition to neurons in the central nervous system, there are glial cells, occupying half the volume of the brain. Peripheral axons are also surrounded by a sheath of glial cells - lemmocytes (Schwann cells). Neurons and glial cells are separated by intercellular clefts that communicate with each other and form a fluid-filled intercellular space of neurons and glia. Through this space there is an exchange of substances between nerve and glial cells.

Neuroglial cells perform many functions: supporting, protective and trophic role for neurons; maintain a certain concentration of calcium and potassium ions in the intercellular space; destroy neurotransmitters and other biologically active substances.

Functions of the central nervous system

The central nervous system performs several functions.

Integrative: The body of animals and humans is a complex highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. This relationship, the unification of the various components of the body into a single whole (integration), their coordinated functioning is provided by the central nervous system.

Coordinating: the functions of various organs and systems of the body must proceed in a coordinated manner, since only with this way of life it is possible to maintain the constancy of the internal environment, as well as successfully adapt to changing environmental conditions. The coordination of the activity of the elements that make up the body is carried out by the central nervous system.

Regulatory: the central nervous system regulates all the processes occurring in the body, therefore, with its participation, the most adequate changes in the work of various organs occur, aimed at ensuring one or another of its activities.

Trophic: the central nervous system regulates trophism, the intensity of metabolic processes in the tissues of the body, which underlies the formation of reactions that are adequate to the ongoing changes in the internal and external environment.

Adaptive: the central nervous system communicates the body with the external environment by analyzing and synthesizing various information coming to it from sensory systems. This makes it possible to restructure the activities of various organs and systems in accordance with changes in the environment. It performs the functions of a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world.

Formation of non-directional behavior: the central nervous system forms a certain behavior of the animal in accordance with the dominant need.

Reflex regulation of nervous activity

The adaptation of the vital processes of an organism, its systems, organs, tissues to changing environmental conditions is called regulation. The regulation provided jointly by the nervous and hormonal systems is called neurohormonal regulation. Thanks to the nervous system, the body carries out its activities on the principle of a reflex.

The main mechanism of the activity of the central nervous system is the response of the body to the actions of the stimulus, carried out with the participation of the central nervous system and aimed at achieving a useful result.

Reflex in Latin means "reflection". The term "reflex" was first proposed by the Czech researcher I.G. Prohaska, who developed the doctrine of reflective actions. The further development of the reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious is accomplished by the type of reflex. But then there were no methods for an objective assessment of brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and he received the name of the method of conditioned reflexes. Using this method, the scientist proved that the basis of the higher nervous activity of animals and humans are conditioned reflexes, which are formed on the basis of unconditioned reflexes due to the formation of temporary connections. Academician P.K. Anokhin showed that the whole variety of animal and human activities is carried out on the basis of the concept of functional systems.

The morphological basis of the reflex is , consisting of several nerve structures, which ensures the implementation of the reflex.

Three types of neurons are involved in the formation of a reflex arc: receptor (sensitive), intermediate (intercalary), motor (effector) (Fig. 6.2). They are combined into neural circuits.

Rice. 4. Scheme of regulation according to the reflex principle. Reflex arc: 1 - receptor; 2 - afferent path; 3 - nerve center; 4 - efferent path; 5 - working body (any organ of the body); MN, motor neuron; M - muscle; KN — command neuron; SN — sensory neuron, ModN — modulatory neuron

The receptor neuron's dendrite contacts the receptor, its axon goes to the CNS and interacts with the intercalary neuron. From the intercalary neuron, the axon goes to the effector neuron, and its axon goes to the periphery to the executive organ. Thus, a reflex arc is formed.

Receptor neurons are located on the periphery and in internal organs, while intercalary and motor neurons are located in the central nervous system.

In the reflex arc, five links are distinguished: the receptor, the afferent (or centripetal) path, the nerve center, the efferent (or centrifugal) path and the working organ (or effector).

The receptor is a specialized formation that perceives irritation. The receptor consists of specialized highly sensitive cells.

The afferent link of the arc is a receptor neuron and conducts excitation from the receptor to the nerve center.

The nerve center is formed by a large number of intercalary and motor neurons.

This link of the reflex arc consists of a set of neurons located in different parts of the central nervous system. The nerve center receives impulses from receptors along the afferent pathway, analyzes and synthesizes this information, and then transmits the generated action program along the efferent fibers to the peripheral executive organ. And the working body carries out its characteristic activity (the muscle contracts, the gland secretes a secret, etc.).

A special link of reverse afferentation perceives the parameters of the action performed by the working organ and transmits this information to the nerve center. The nerve center is the action acceptor of the back afferent link and receives information from the working organ about the completed action.

The time from the beginning of the action of the stimulus on the receptor until the appearance of a response is called the reflex time.

All reflexes in animals and humans are divided into unconditioned and conditioned.

Unconditioned reflexes - congenital, hereditary reactions. Unconditioned reflexes are carried out through reflex arcs already formed in the body. Unconditioned reflexes are species-specific, i.e. common to all animals of this species. They are constant throughout life and arise in response to adequate stimulation of the receptors. Unconditioned reflexes are also classified according to their biological significance: food, defensive, sexual, locomotor, indicative. According to the location of the receptors, these reflexes are divided into: exteroceptive (temperature, tactile, visual, auditory, gustatory, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscular, tendon, etc.). By the nature of the response - to motor, secretory, etc. By finding the nerve centers through which the reflex is carried out - to the spinal, bulbar, mesencephalic.

Conditioned reflexes - reflexes acquired by the organism in the course of its individual life. Conditioned reflexes are carried out through newly formed reflex arcs on the basis of reflex arcs of unconditioned reflexes with the formation of a temporary connection between them in the cerebral cortex.

Reflexes in the body are carried out with the participation of endocrine glands and hormones.

At the heart of modern ideas about the reflex activity of the body is the concept of a useful adaptive result, to achieve which any reflex is performed. Information about the achievement of a useful adaptive result enters the central nervous system through the feedback link in the form of reverse afferentation, which is an essential component of reflex activity. The principle of reverse afferentation in reflex activity was developed by P.K. Anokhin and is based on the fact that the structural basis of the reflex is not a reflex arc, but a reflex ring, which includes the following links: receptor, afferent nerve pathway, nerve center, efferent nerve pathway, working organ , reverse afferentation.

When any link of the reflex ring is turned off, the reflex disappears. Therefore, the integrity of all links is necessary for the implementation of the reflex.

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

Excitation in the nerve centers spreads unilaterally from the receptor to the effector, which is associated with the ability to conduct excitation only from the presynaptic membrane to the postsynaptic one.

Excitation in the nerve centers is carried out more slowly than along the nerve fiber, as a result of slowing down the conduction of excitation through the synapses.

In the nerve centers, summation of excitations can occur.

There are two main ways of summation: temporal and spatial. At temporary summation several excitatory impulses come to the neuron through one synapse, are summed up and generate an action potential in it, and spatial summation manifests itself in the case of receipt of impulses to one neuron through different synapses.

In them, the rhythm of excitation is transformed, i.e. a decrease or increase in the number of excitation impulses leaving the nerve center compared to the number of impulses coming to it.

The nerve centers are very sensitive to the lack of oxygen and the action of various chemicals.

Nerve centers, unlike nerve fibers, are capable of rapid fatigue. Synaptic fatigue during prolonged activation of the center is expressed in a decrease in the number of postsynaptic potentials. This is due to the consumption of the mediator and the accumulation of metabolites that acidify the environment.

The nerve centers are in a state of constant tone, due to the continuous flow of a certain number of impulses from the receptors.

Nerve centers are characterized by plasticity - the ability to increase their functionality. This property may be due to synaptic facilitation - improved conduction in synapses after a short stimulation of the afferent pathways. With frequent use of synapses, the synthesis of receptors and mediator is accelerated.

Along with excitation, inhibitory processes occur in the nerve center.

CNS coordination activity and its principles

One of the important functions of the central nervous system is the coordination function, which is also called coordination activities CNS. It is understood as the regulation of the distribution of excitation and inhibition in neuronal structures, as well as the interaction between nerve centers, which ensure the effective implementation of reflex and voluntary reactions.

An example of the coordination activity of the central nervous system can be the reciprocal relationship between the centers of respiration and swallowing, when during swallowing the center of respiration is inhibited, the epiglottis closes the entrance to the larynx and prevents food or liquid from entering the airways. The coordination function of the central nervous system is fundamentally important for the implementation of complex movements carried out with the participation of many muscles. Examples of such movements can be the articulation of speech, the act of swallowing, gymnastic movements that require the coordinated contraction and relaxation of many muscles.

Principles of coordination activities

• Reciprocity - mutual inhibition of antagonistic groups of neurons (flexor and extensor motoneurons)
• End neuron - activation of an efferent neuron from different receptive fields and competition between different afferent impulses for a given motor neuron
• Switching - the process of transferring activity from one nerve center to the antagonist nerve center
• Induction - change of excitation by inhibition or vice versa
• Feedback is a mechanism that ensures the need for signaling from the receptors of the executive organs for the successful implementation of the function
• Dominant - a persistent dominant focus of excitation in the central nervous system, subordinating the functions of other nerve centers.

The coordination activity of the central nervous system is based on a number of principles.

Convergence principle is realized in convergent chains of neurons, in which the axons of a number of others converge or converge on one of them (usually efferent). Convergence ensures that the same neuron receives signals from different nerve centers or receptors of different modalities (different sense organs). On the basis of convergence, a variety of stimuli can cause the same type of response. For example, the watchdog reflex (turning the eyes and head - alertness) can be caused by light, sound, and tactile influences.

The principle of a common final path follows from the principle of convergence and is close in essence. It is understood as the possibility of implementing the same reaction triggered by the final efferent neuron in the hierarchical nervous circuit, to which the axons of many other nerve cells converge. An example of a classic final pathway is the motor neurons of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves, which directly innervate the muscles with their axons. The same motor response (for example, bending the arm) can be triggered by the receipt of impulses to these neurons from the pyramidal neurons of the primary motor cortex, neurons of a number of motor centers of the brain stem, interneurons of the spinal cord, axons of sensory neurons of the spinal ganglia in response to the action of signals perceived by different sense organs (to light, sound, gravitational, pain or mechanical effects).

Principle of divergence is realized in divergent chains of neurons, in which one of the neurons has a branching axon, and each of the branches forms a synapse with another nerve cell. These circuits perform the functions of simultaneously transmitting signals from one neuron to many other neurons. Due to divergent connections, signals are widely distributed (irradiated) and many centers located at different levels of the CNS are quickly involved in the response.

The principle of feedback (reverse afferentation) consists in the possibility of transmitting information about the ongoing reaction (for example, about movement from muscle proprioceptors) back to the nerve center that triggered it, via afferent fibers. Thanks to feedback, a closed neural circuit (circuit) is formed, through which it is possible to control the progress of the reaction, adjust the strength, duration and other parameters of the reaction, if they have not been implemented.

The participation of feedback can be considered on the example of the implementation of the flexion reflex caused by mechanical action on skin receptors (Fig. 5). With reflex contraction of the flexor muscle, the activity of proprioreceptors and the frequency of sending nerve impulses along the afferent fibers to the a-motoneurons of the spinal cord, which innervate this muscle, change. As a result, a closed control loop is formed, in which the role of the feedback channel is played by afferent fibers that transmit information about the contraction to the nerve centers from the muscle receptors, and the role of the direct communication channel is played by the efferent fibers of motor neurons going to the muscles. Thus, the nerve center (its motor neurons) receives information about the change in the state of the muscle caused by the transmission of impulses along the motor fibers. Thanks to the feedback, a kind of regulatory nerve ring is formed. Therefore, some authors prefer to use the term "reflex ring" instead of the term "reflex arc".

The presence of feedback is important in the mechanisms of regulation of blood circulation, respiration, body temperature, behavioral and other reactions of the body and is discussed further in the relevant sections.

Rice. 5. Feedback scheme in neural circuits of the simplest reflexes

The principle of reciprocal relations is realized in the interaction between the nerve centers-antagonists. For example, between a group of motor neurons that control arm flexion and a group of motor neurons that control arm extension. Due to reciprocal relationships, excitation of neurons in one of the antagonistic centers is accompanied by inhibition of the other. In the given example, the reciprocal relationship between the flexion and extension centers will be manifested by the fact that during the contraction of the flexor muscles of the arm, an equivalent relaxation of the extensor muscles will occur, and vice versa, which ensures smooth flexion and extension movements of the arm. Reciprocal relations are carried out due to the activation of inhibitory interneurons by the neurons of the excited center, the axons of which form inhibitory synapses on the neurons of the antagonistic center.

Dominant principle is also realized on the basis of the characteristics of the interaction between the nerve centers. The neurons of the dominant, most active center (center of excitation) have persistent high activity and suppress excitation in other nerve centers, subjecting them to their influence. Moreover, the neurons of the dominant center attract afferent nerve impulses addressed to other centers and increase their activity due to the receipt of these impulses. The dominant center can be in a state of excitation for a long time without signs of fatigue.

An example of a state caused by the presence of a dominant focus of excitation in the central nervous system is the state after an important event experienced by a person, when all his thoughts and actions somehow become connected with this event.

Dominant Properties

• Hyperexcitability
• Excitation persistence
• Excitation inertia
• Ability to suppress subdominant foci
• Ability to sum excitations

The considered principles of coordination can be used, depending on the processes coordinated by the CNS, separately or together in various combinations.

In order to cope with such various duties, the human nervous system must have an appropriate structure.

In the human nervous system, there are:
- central nervous system;
- peripheral nervous system.

Purpose of the peripheral nervous system- connect the central nervous system with the sensory receptors of the body and muscles. It includes the autonomic (autonomous) and somatic nervous systems.

somatic nervous system is intended for the implementation of voluntary, conscious sensory and motor functions. Its task is to transmit sensory signals caused by external stimuli to the central nervous system and control the movements corresponding to these signals.

autonomic nervous system- this is a kind of "autopilot", automatically supporting the modes of operation of the blood vessels of the heart, respiratory organs, digestion, urination and endocrine glands. The activity of the autonomic nervous system is subordinated to the brain centers of the human nervous system.

The human nervous system:
- Departments of the nervous system
1) Central
- Brain
- Spinal cord
2) Peripheral
- Somatic system
- Vegetative (autonomous) system
1) Sympathetic system
2) Parasympathetic system

In the autonomic system, the sympathetic and parasympathetic nervous systems are distinguished.

Sympathetic nervous system It is a weapon of self defense. In situations requiring a quick response (especially in situations of danger), the sympathetic nervous system:
- inhibits the activity of the digestive system as irrelevant at the moment (in particular, reduces the blood circulation of the stomach);
- increases the content of adrenaline and glucose in the blood, thereby expanding the blood vessels of the heart, brain and skeletal muscles;
- mobilizes the work of the heart, increasing blood pressure and the rate of its coagulation in order to avoid possible large blood loss;
- dilates the pupils and palpebral fissures, forming the appropriate facial expressions.

parasympathetic nervous system is included in the work when the tense situation subsides and the time comes for peace and relaxation. All processes caused by the action of the sympathetic system are restored. The normal functioning of these systems is characterized by their dynamic equilibrium. Violation of this balance occurs when one of the systems is overexcited. With prolonged and frequent states of overexcitation of the sympathetic system, there is a threat of a chronic increase in blood pressure (hypertension), angina pectoris and other pathological disorders.

In case of overexcitation of the parasympathetic system, gastrointestinal diseases may appear (the occurrence of attacks of bronchial asthma and exacerbation of ulcer pain during night sleep are explained by the increased activity of the parasympathetic system at this time of day and inhibition of the sympathetic system).

There is a possibility of volitional regulation of vegetative functions with the help of special methods of suggestion and self-hypnosis (hypnosis, autogenic training, etc.). However, in order to avoid harm to the body (and the psyche), this requires caution and conscious possession of psychological technologies of this kind.

The central nervous system includes:
- brain;
- spinal cord.

Anatomically, they are located in the skull and spine. The bones of the skull and spine protect the brain from physical injury.

The spinal cord is a long column of nerve tissue that runs through the spinal canal, from the second lumbar vertebra to the medulla oblongata. It solves two main tasks:
- transmits sensory information from peripheral receptors to the brain;
- provides the body's response to external and internal signals through the activation of the muscular system. The spinal cord is formed by 31 identical blocks ~ segments connected to different parts of the human body. Each of the segments consists of gray and white matter. The white matter forms the ascending, descending and internal nerve pathways. The former transmit information to the brain, the latter - from the brain to various parts of the body, the third - from segment to segment.

The structure of the gray matter is formed by the nuclei of the spinal nerves, extending from each of the segments. In turn, each spinal nerve consists of a sensory and a motor nerve. The first perceives sensory information from the receptors of internal organs, muscles and skin. The second transmits motor excitation from the spinal nerves to the periphery of the human body.

The brain is the highest instance of the nervous system. It is the largest division of the central nervous system. The mass of the brain is not an informative indicator of the level of intellectual development of its owner. So, in relation to the body, the human brain is 1/45 part, the brain of a monkey is 1/25, the brain of a whale is 1/10,000 part. The absolute weight of the brain in men is about 1400 g, in women - 1250 g.

The mass of the brain changes during a person's life. Starting with a weight of 350 g (in newborns), the brain “gains” maximum weight by age 25, then keeps it constant until the age of 50, and then begins to “lose weight” by an average of 30 g in each subsequent decade. All these parameters depend on a person's belonging to a particular race (however, there is no correlation with the level of intelligence here). For example, the maximum brain weight of a Japanese is observed at 30-40 years old, a European - by 20-25 years old.

The structure of the brain includes: anterior, middle, posterior and medulla oblongata.

Modern ideas associate the development of the human brain with three levels:
- the highest level - the forebrain;
- middle level - middle brain;
- lower level - hindbrain.

Forebrain. All parts of the brain work together, but the "central control" of the nervous system is located in the forebrain, which consists of the cerebral cortex, diencephalon, and olfactory brain (Fig. 4). It is here that most of the neurons are located and strategic tasks for managing processes are formed, as well as commands for their execution. The implementation of commands is taken over by the middle and lower levels. At the same time, the commands of the cerebral cortex can be innovative in nature, be completely unusual. The lower levels work out these commands according to the habitual for a person, "well-worn" programs. This "division of labor" has developed historically.

Representatives of the materialistic concept argue that the anterior part of the brain arose as a result of the evolution of the sense of smell. At the moment, he controls the instinctive (genetically conditioned), individual and collective (conditioned by labor activity and speech) forms of human behavior. The collective form of behavior caused the appearance of new superficial layers of the cerebral cortex. There are six such layers in total, each of which consists of the same type of nerve cells, which have their own shape and orientation. Occurred by time<дения принято различать древнюю, старую и новую кору. Древняя кора занимает около 0,6 % площади всей коры и состоит из одного слоя нейронов. Площадь старой коры - 2,6 %. Остальная площадь принадлежит новой коре.

Outwardly, the bark resembles a walnut kernel: a wrinkled surface with numerous convolutions and furrows. This configuration is the same for all people. Under the cortex are located the right and left hemispheres of the brain, which account for about 80% of the weight of the entire brain. The hemispheres are filled with axons connecting cortical neurons with neurons in other parts of the brain. Each hemisphere of the brain consists of the frontal, temporal, parietal, and occipital lobes that function together.

In connection with the role played by the cerebral cortex in the mental life of a person, it is advisable to consider in more detail the functions that it performs.

In the cortex, several functional zones (centers) associated with the performance of certain functions are conventionally distinguished.

Each of the sensory (primary projective) zones receives signals from "its" sense organs and is directly involved in the formation of sensations. The visual and auditory sensory areas are located separately from the others. Damage to the sensory areas causes a loss of a certain type of sensitivity (hearing, vision, etc.).

Motor zones set in motion various parts of the body. By irritating sections of the motor zones with a weak electric current, various organs can be forced to move (even against the will of a person) (lips stretch in a smile, arm bend, etc.).

Damage to areas of this zone is accompanied by partial or complete paralysis.

The so-called basal nodes located under the frontal lobes take part in the regulation of voluntary and involuntary movements. The consequences of their defeat are convulsions, tics, twitching, masking of the face, muscle trembling, etc.

Associative (integrative) zones are able to simultaneously respond to signals from several sense organs and form integral perceptual images (perception). These zones do not have clearly defined boundaries (in any case, the boundaries have not yet been established). When the associative zones are affected, signs of a different kind appear: sensitivity to a certain type of stimulus (visual, auditory, etc.) is preserved, but the ability to correctly assess the value of the acting stimulus is impaired. So:
- damage to the visual association zone leads to “word blindness”, when vision is preserved, but the ability to understand what you see is lost (a person can read a word, but not understand its meaning);
- if the auditory associative zone is damaged, a person hears, but does not understand the meaning of words (verbal deafness);
- disruption of the tactile associative zone leads to the fact that a person is not able to recognize objects by touch;
damage to the associative zones of the frontal lobe leads to a loss of the ability to plan and predict events while maintaining memory and skills;
- injuries of the frontal lobe dramatically change the character of the individual in the direction of intemperance, rudeness and promiscuity, while maintaining other abilities necessary for the daily life of the individual.

Autonomous centers of speech, strictly speaking, do not exist. Here they often talk about the center of auditory perception of speech (Wernicke's center) and the motor center of speech (Broca's center). The representation of the speech function in most people is located in the left hemisphere in the region of the third gyrus of the cortex. This is evidenced by the facts of violation of the processes of speech formation in case of damage to the frontal lobe and loss of speech understanding in case of damage to the posterior parts of the lobe. The "capture" of the functions of speech (and with it the functions of logical thinking, reading and writing) by the left hemisphere is called the functional asymmetry of the brain.

The right hemisphere got the processes associated with the regulation of feelings. In this regard, the right hemisphere is involved in the formation of a holistic image of the object. The left is designed to analyze the little things in the perception of the object, that is, it forms the image of the object sequentially, in detail. It is the "spokesman" of the brain. But information processing takes place in close cooperation between both hemispheres: as soon as one hemisphere refuses to work, the other turns out to be helpless.

The diencephalon patronizes the activity of the sense organs, regulates all autonomic functions. Its composition:
- thalamus (visual tubercle);
- hypothalamus (hypothalamus).

The thalamus (visual tubercle) is a sensory control center for information flows, the largest "transport" node of the nervous system. The main function of the thalamus is to receive information from sensory neurons (from the eyes, ears, tongue, skin, internal organs, except for smell) and transmit it to the higher parts of the brain.

The hypothalamus (hypothalamus) controls the functioning of internal organs, endocrine glands, metabolic processes, and body temperature. This is where the emotional states of a person are formed. The hypothalamus influences human sexual behavior.

The olfactory brain is the smallest part of the forebrain, providing the function of smell, marked by the gray millennia of the evolution of the human psyche.

The midbrain is located between the hindbrain and diencephalon (see Fig. 3). Here are the primary centers of vision and hearing, as well as nerve fibers connecting the spinal cord and medulla oblongata with the cerebral cortex. The midbrain includes a significant part of the limbic system (visceral brain). The elements of this system are the hippocampus and tonsils.

The medulla oblongata is the lowest part of the brain. Anatomically, it is a continuation of the spinal cord. The "duties" of the medulla oblongata include:
- coordination of movements, regulation of respiration, heartbeat, tone of blood vessels, etc.;
- regulation by reflex acts of chewing, swallowing, sucking, vomiting, blinking and coughing;
- control of body balance in space.

The hindbrain is located between the middle and oblong. Consists of the cerebellum and the pons. The bridge contains the centers of the auditory, vestibular, skin and muscle sensory systems, autonomic centers for the regulation of the lacrimal and salivary glands. He is involved in the implementation and development of complex forms of movements.

An important role in the work of the human nervous system is played by the reticular (mesh) formation, which is located in the spinal, medulla oblongata and hindbrain. Its influence extends to the activity of the brain, the state of the cortex and subcortical structures of the brain, cerebellum, and spinal cord. This is the source of the body's activity, its performance. Its main functions:
- maintenance of a waking state;
- increased tone of the cerebral cortex;
- selective inhibition of the activity of certain parts of the brain (auditory and visual centers of subcortical structures), which is important for controlling attention;
- formation of standard adaptive forms of response to familiar external stimuli;
- the formation of orienting reactions to unusual external stimuli, on the basis of which reactions of the first type can be formed and the normal functioning of the body is ensured.

Violation of the work of this formation leads to failures of the biorhythms of the body. For example, a person cannot fall asleep for a long time or, conversely, sleep becomes very long.

The hippocampus plays a significant role in memory processes. Violation of its work leads to deterioration or complete loss of short-term memory. Long-term memory is not affected. The hippocampus is believed to be involved in the transfer of information from short-term memory to long-term memory. In addition, it participates in the formation of emotions, which ensures reliable memorization of the material.

The tonsils are two clusters of neurons that influence feelings of aggressiveness, rage, and fear. However, the tonsils are not the center of these feelings. Even Aristotle tried to localize feelings (the soul ejects a thought, the body gives rise to various sensations, and the heart is the receptacle for feelings, passions, mind and voluntary movements). Thomas Aquinas supported his idea. Descartes argued that feelings of joy and danger are generated by the pineal gland, which then transmits them to the soul, brain and heart. The hypothesis of I. M. Sechenov is that emotions are a systemic phenomenon.

The first experimental attempts to link emotions with the work of certain parts of the brain (to localize emotions) were made by V. M. Bekhterev. By stimulating parts of the birds' thalamus, he analyzed the emotional content of their motor reactions. Subsequently, V. Cannon and P. Bard (USA) gave the thalamus a decisive role in the formation of emotions. Even later, E. Gelgorn and J. Lufborrow came to the conclusion that the hypothalamus is the main center for the formation of emotions.

Experimental studies conducted by S. Olds and P. Milner (USA) on rats made it possible to single out the zones of "heaven" and "hell" in them. It turned out that about 35% of brain points are responsible for the formation of a feeling of pleasure, 5% cause a feeling of displeasure and 60% remain neutral regarding these feelings. Naturally, these results cannot be fully transferred to the human psyche.

With the penetration into the secrets of the psyche, the opinion that the organization of emotions is a widely branched system of nervous formations became more and more strengthened. At the same time, the main functional role of negative emotions is to preserve a person as a species, and positive ones - to acquire new properties. If negative emotions were not necessary for survival, then they would simply disappear from the psyche. The main control and regulation of emotional behavior is carried out by the frontal lobes of the cerebral cortex.

The search for areas responsible for certain mental states and processes is still ongoing. Moreover, the problem of localization has grown into a psychophysiological problem.

CNS - what is it? The structure of the human nervous system is described as an extensive electrical network. Perhaps this is the most accurate metaphor possible, since a current really runs through thin threads-fibers. Our cells themselves generate microdischarges in order to quickly deliver information from receptors and sensory organs to the brain. But the system does not function by chance, everything is subject to a strict hierarchy. That is why they single out

Departments of the central nervous system

Let's consider this system in more detail. And yet, the central nervous system - what is it? Medicine provides an exhaustive answer to this question. This is the main part of the nervous system of chordates and humans. It consists of structural units - neurons. In invertebrates, this whole structure is similar to a cluster of nodules that do not have a clear subordination to each other.

The human central nervous system is represented by a bundle of the brain and spinal cord. In the latter, the cervical, thoracic, lumbar and sacrococcygeal regions are distinguished. They are located in the corresponding parts of the body. Almost all peripheral nerve impulses are conducted to the spinal cord.

The brain is also divided into several parts, each of which has a specific function, but coordinates their work with the neocortex, or the cerebral cortex. So, anatomically distinguish:

• brain stem;
• medulla;
• hindbrain (pons and cerebellum);
• midbrain (lamina of the quadrigemina and legs of the brain);
• forebrain

Each of these parts will be discussed in more detail below. Such a structure of the nervous system was formed in the process of human evolution so that he could ensure his existence in the new conditions of life.

Spinal cord

It is one of the two organs of the CNS. The physiology of its work does not differ from that in the brain: with the help of complex chemical compounds (neurotransmitters) and the laws of physics (in particular, electricity), information from small branches of nerves is combined into large trunks and either implemented in the form of reflexes in the corresponding section of the spinal cord, or enters the brain for further processing.

It is located in the hole between the arches and the bodies of the vertebrae. It is protected, like the head, by three shells: hard, arachnoid and soft. The space between these tissue sheets is filled with a fluid that nourishes the nervous tissue, and also acts as a shock absorber (muffles vibrations during movements). The spinal cord starts from the opening in the occipital bone, on the border with the medulla oblongata, and ends at the level of the first or second lumbar vertebra. Further there are only membranes, cerebrospinal fluid and long nerve fibers ("ponytail"). Conventionally, anatomists divide it into departments and segments.

On the sides of each segment (corresponding to the height of the vertebrae), sensory and motor nerve fibers, called roots, depart. These are long processes of neurons whose bodies are located directly in the spinal cord. They are a collector of information from other parts of the body.

Medulla

The medulla oblongata is also active. It is part of such a formation as the brain stem, and is in direct contact with the spinal cord. There is a conditional border between these anatomical formations - this is a decussation. It is separated from the bridge by a transverse groove and a section of the auditory pathways that pass in the rhomboid fossa.

In the thickness of the medulla oblongata are the nuclei of the 9th, 10th, 11th and 12th cranial nerves, fibers of the ascending and descending nerve pathways and the reticular formation. This area is responsible for the implementation of protective reflexes, such as sneezing, coughing, vomiting and others. It also keeps us alive by regulating our breathing and heartbeat. In addition, the medulla oblongata contains centers for regulating muscle tone and maintaining posture.

Bridge

Together with the cerebellum, it is the posterior part of the CNS. What is it? An accumulation of neurons and their processes located between the transverse sulcus and the exit point of the fourth pair of cranial nerves. It is a roller-shaped thickening with a depression in the center (there are vessels in it). From the middle of the bridge exit the fibers of the trigeminal nerve. In addition, the upper and middle cerebellar peduncles depart from the bridge, and the nuclei of the 8th, 7th, 6th, and 5th pair of cranial nerves, the auditory pathway, and the reticular formation are located in the upper part of the pons.

The main function of the bridge is to transmit information to the higher and lower parts of the central nervous system. Many ascending and descending paths pass through it, which end or begin their journey in different parts of the cerebral cortex.

Cerebellum

This is the part of the CNS (central nervous system), which is responsible for coordinating movements, maintaining balance and maintaining muscle tone. It is located between the pons and the midbrain. To obtain information about the environment, it has three pairs of legs in which nerve fibers pass.

The cerebellum acts as an intermediate collector of all information. It receives signals from sensory fibers of the spinal cord, as well as from motor fibers starting in the cortex. After analyzing the received data, the cerebellum sends impulses to the motor centers and corrects the position of the body in space. All this happens so quickly and smoothly that we do not notice his work. All our dynamic automatisms (dancing, playing musical instruments, writing) are the responsibility of the cerebellum.

midbrain

In the human CNS there is a department that is responsible for visual perception. It is the midbrain. It consists of two parts:

• The lower one is the legs of the brain, in which the pyramidal pathways pass.
• The upper one is the plate of the quadrigemina, on which, in fact, the visual and auditory centers are located.

The formations in the upper part are closely connected with the diencephalon, so there is not even an anatomical boundary between them. It can be conditionally assumed that this is the posterior commissure of the cerebral hemispheres. In the depths of the midbrain are the nuclei of the third cranial nerve - the oculomotor, and besides this, the red nucleus (it is responsible for controlling movements), the black substance (initiates movements) and the reticular formation.

The main functions of this area of ​​the CNS:

• orienting reflexes (reaction to strong stimuli: light, sound, pain, etc.);
• vision;
• pupil reaction to light and accommodation;
• friendly turn of the head and eyes;
• maintenance of skeletal muscle tone.

diencephalon

This formation is located above the midbrain, immediately below the corpus callosum. It consists of the thalamic part, the hypothalamus and the third ventricle. The thalamic part includes the thalamus proper (or thalamus), the epithalamus, and the metathalamus.

• The thalamus is the center of all types of sensitivity; it collects all afferent impulses and redistributes them into the corresponding motor pathways.
• The epithalamus (pineal gland, or pineal gland) is an endocrine gland. Its main function is the regulation of human biorhythms.
• The metathalamus is formed by the medial and lateral geniculate bodies. The medial bodies represent the subcortical center of hearing, and the lateral bodies represent vision.

The hypothalamus controls the pituitary gland and other endocrine glands. In addition, it regulates partly the autonomic nervous system. For the speed of metabolism and maintenance of body temperature, we must thank him. The third ventricle is a narrow cavity that contains the fluid necessary to feed the central nervous system.

The cortex of the hemispheres

Neocortex CNS - what is it? This is the youngest part of the nervous system, phylo - and ontogenetically it is one of the last to be formed and represents rows of cells densely layered on top of each other. This area occupies about half of the entire space of the cerebral hemispheres. It contains convolutions and furrows.

There are five parts of the cortex: frontal, parietal, temporal, occipital and insular. Each of them is responsible for their area of ​​work. For example, in the frontal lobe are the centers of movement and emotions. In the parietal and temporal - the centers of writing, speech, small and complex movements, in the occipital - visual and auditory, and the insular lobe corresponds to balance and coordination.

All information that is perceived by the endings of the peripheral nervous system, whether it be smell, taste, temperature, pressure or anything else, enters the cerebral cortex and is carefully processed. This process is so automated that when, in view of pathological changes, it stops or gets upset, the person becomes disabled.

CNS functions

For such a complex formation as the central nervous system, the functions corresponding to it are also characteristic. The first of them is integrative-coordinating. It implies the coordinated work of various organs and systems of the body to maintain the constancy of the internal environment. The next function is the connection between a person and his environment, adequate reactions of the body to physical, chemical or biological stimuli. It also includes social activities.

The functions of the central nervous system also cover metabolic processes, their speed, quality and quantity. To do this, there are separate structures, such as the hypothalamus and pituitary gland. Higher mental activity is also possible only thanks to the central nervous system. When the cortex dies, the so-called “social death” is observed, when the human body still remains viable, but as a member of society it no longer exists (it cannot speak, read, write and perceive other information, as well as reproduce it).

It is difficult to imagine humans and other animals without the central nervous system. Its physiology is complex and not yet fully understood. Scientists are trying to figure out how the most complex biological computer ever worked. But this is like "a bunch of atoms studying other atoms," so advances in this area are not yet sufficient.

Each cell, system and internal organ is a single whole, in order to ensure the interaction and coordinated work of all organs, the central nervous system is necessary. This element of the organism is presented in the form of structural and functional units and processes branching from them of various lengths and purposes.

The central nervous system is formed from several components - this is the brain and spinal cord, interacting through the peripheral part of the nervous system. The human central nervous system is responsible for the following feelings and sensations:

• organs of hearing and vision, perception of sounds and light, response to external stimuli;
• smell and touch, through which the outside world and the environment are perceived;
• emotionality, susceptibility;
• memory and thought processes of the body, intellectual activity.

The brain structure of the CNS consists of gray and white matter. The gray substance is represented by nerve cells with small branching processes. This substance occupies the center of the spinal cord, affecting the spinal canal. In the brain, the gray matter is the main component of the cortex, having scattered formations in the essence of white. The white layer is located under the gray and is structurally formed from fibers involved in the formation of nerve bundles. Similar bundles of bundles line up the nerve.

Shells of the CNS

Surround the central NS shells, each of which is different:

1. Solid - external. It is this shell that is formed inside the cranial cavity, as well as inside the hollow formation of the spinal column.
2. Spider cover. This shell is equipped with nerve endings and blood vessels, located under the outer shell.
3. Vascular. Between the second and third membranes there is another cavity, the space of which is filled with medulla. The choroid, based on the name, is formed from a combination of arteries, capillaries, veins that perform the functions of blood vessels. This cover is directly connected to the brain, penetrating into its folds.

Brain

This organ has a simple structure and is represented by the following elements: an extended formation - the trunk, a small brain called the cerebellum, which takes responsibility for muscle tone, coordination and balance, as well as large hemispheres.

The main element, which includes the higher centers representing reason, mental abilities, speech abilities, is the cerebral hemispheres. Each of them is formed from a nucleus with gray matter, a white shell and a cerebral cortex that protects the remaining layers.

The cerebellum, which provides coordinated actions, is represented by gray matter, a sheath of white matter, and a layer of gray located from the outside.

The trunk is a part that has no separation by layers, is formed from a single array that is not divided into colors. This part communicates directly with the rest and corrects the work of breathing, circulatory systems, movement and feelings.

Spinal cord

This cylindrical organ is located in the bowels of the spinal column, has protection in the form of bone tissue formation. The spinal cord itself is under the membranes.

If you look at the organ in section, you can see the gray matter in the form of a butterfly or in shape resembling H, it is covered with a white shell on top. Some of the pathways originate in white matter and end in gray matter and vice versa. Many fibers located in the white array of the membrane organize the interaction of many sections of the gray matter located in the spinal cord.

Functionality of the CNS

The device of any individual is represented by many structures and organs interacting with each other, but all of them are aimed at contributing to the normal functioning of the human device, its protection, support, nutrition. The interconnection of systems among themselves provides the central nervous system. It is she who is the regulator of the processes that take place in the body, with her help the direction of work changes, the pace of functioning is set and all the conditions necessary for this are provided.

The central nervous system performs a number of basic functions, without which the body cannot exist:

1. Integration. Occurs due to the combination of functions. Integration is divided into 3 forms:

• nervous - association of departments of the central nervous system. For example, let's take food that has color and aroma, which is a conditioned reflex stimulus. Various reflexes occur in the body at the sight of food: saliva is secreted, gastric juice is produced. In this particular case, a combination of behavioral, nutritional and bodily prescriptions can be observed;
• humoral. It is a combination of various functions based on body fluids together with hormones. For example, various hormones of internal secretions tend to act synchronously, only increasing the action of each other, but there is a variant of sequential production, when one hormone increases the action of another. The process ends with the activation of a number of different functions. So, adrenaline can develop an increase in heart rate, increase blood glucose levels, start lung ventilation, etc .;
• mechanical. This shape is necessary to perform a specific function that ensures the structural integrity of the organ. If any of the organs or parts of the body is injured, then structural changes are formed, which further leads to a malfunction of the whole organism.

1. Correlation. It is necessary in order to most effectively form the relationship between systems, internal organs and processes, to bring them together.
2. Regulation. Ensuring the work of the entire central nervous system, it is necessary to regulate and monitor the main indicators of the body. The basis of this regulation is reflexes, the formation and organization of processes, self-regulation, thanks to which the body adapts to the constantly changing internal conditions of the surrounding world. It flows in forms that correct along the way, and nutritious. All kinds of influences are exerted by the nerve processes related to the body and to excitation.
3. Coordination. Synchronization and coordination of actions of all parts of one single system. Change of position or posture, various forms of movement, movement in space, adaptability of reactions to what is happening, labor activity, physical activity - all these components must be clearly coordinated and directed by the central nervous system.
4. Communication with the environment. The central nervous system is a center that forms a connection and transfers data from the outside world to the organs and systems of the body for subsequent coordinated actions.
5. Knowledge and adaptation. In order to adapt to certain circumstances, to choose the right model of behavior in special situations at this moment, to adapt to the activity, this function of the central nervous system is necessary. With the help of this system, a comfortable adaptation to the circumstances surrounding a person is ensured.

Possible problems

Damage and malfunctions in the functioning of the central nervous system are not uncommon, and therefore can occur for various reasons:

• genetic predisposition, congenital defects and disorders;
• injury or mechanical damage;
• inflammatory processes;
• viral infections;
• tumor formations, oncology;
• circulatory disorders, vascular pathologies, etc.

Often these pathological changes appear even in the womb, because many negative factors can affect the fetus:

• infectious diseases of a woman during pregnancy, which were not completed or not detected in time;
• injuries, incl. during difficult childbirth;
• radioactive exposure;
• toxic effects, intoxication;
• exposure to alcohol or drugs.

Heredity is fraught with the greatest danger, it is especially important to take care of pregnancy in the first months of pregnancy, because it is during this period that the female body is subject to changes and forms the child's nervous system. The fetus may develop hydrocephalus or microcephaly, which is fraught with dangerous consequences and will require long and expensive treatment in the future. And they can also make the child disabled for life.

The structure of the central nervous system has many complexities and parts responsible for the work. Therefore, any even minor deviations from the norm can serve as an obstacle to the full-fledged work of the whole organism. That is why it is necessary to listen to your body, recognize its danger signals in a timely manner, and eliminate malfunctions and malfunctions in the operation and interaction of individual parts.

It is important to plan the day correctly, correctly distribute the resources of the body, allocate time for proper rest and sleep. An important role is played by the diet, which should be balanced and natural. Breathe fresh air daily and do simple physical exercises that will help keep the body in shape and the body in harmony.

In the nervous system of humans and vertebrates, two large sections are distinguished - the central nervous system and the peripheral nervous system. The central nervous system (CNS) is the brain and spinal cord. Everything that lies outside the brain and spinal cord belongs to the peripheral nervous system - these are numerous nerves and ganglions.

The peripheral nervous system (PNS) connects the central nervous system to the organs and limbs. The neurons of the peripheral nervous system are located outside the central nervous system - the brain and spinal cord.

Unlike the central nervous system, the peripheral nervous system is not protected by the bones or the blood-brain barrier, and can be subject to mechanical damage and toxins.

The peripheral nervous system is functionally and structurally divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system is responsible for coordinating body movements as well as receiving external stimuli. It is a system that regulates consciously controlled activities. The autonomic nervous system is divided into the sympathetic nervous system, parasympathetic nervous system and enteric nervous system. The sympathetic nervous system is responsible for responding to impending danger or stress and, along with other physiological changes, is responsible for increasing the pulse rate and blood pressure, and also increases the level of adrenaline when a feeling of excitement arises. The parasympathetic nervous system, on the other hand, becomes noticeable when a person is resting and feeling relaxed, it is responsible for such things as constriction of the pupils, slowing of the heartbeat, dilation of blood vessels, and stimulation of the digestive and genitourinary systems. The role of the enteric nervous system is to control all aspects of digestion, from the esophagus to the stomach, small intestine, and rectum.

Central nervous system (CNS)- the main part of the nervous system of animals and humans, consisting of neurons and their processes; it is represented in invertebrates by a system of closely interconnected nerve nodes (ganglia), in vertebrates and humans - by the spinal cord and brain.

The main and specific function of the central nervous system is the implementation of simple and complex highly differentiated reflective reactions, called reflexes. In higher animals and humans, the lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - regulate the activity of individual organs and systems of a highly developed organism, communicate and interact between them, ensure the unity of the organism and the integrity of its activity. The highest department of the central nervous system - the cerebral cortex and the nearest subcortical formations - mainly regulates the connection and relationship of the body as a whole with the environment

The central nervous system is connected with all organs and tissues through the peripheral nervous system, which in vertebrates includes cranial nerves extending from the brain, and spinal nerves - from the spinal cord, intervertebral nerve nodes, as well as the peripheral part of the autonomic nervous system - nerve nodes, with suitable to them (preganglionic, from the Latin ganglion) and outgoing from them (postganglionic) nerve fibers. Sensitive, or afferent, nerve adductor fibers carry excitation to the central nervous system from peripheral receptors; along the efferent efferent (motor and autonomic) nerve fibers, excitation from the central nervous system is directed to the cells of the executive working apparatus (muscles, glands, blood vessels, etc.). In all parts of the CNS there are afferent neurons that perceive stimuli coming from the periphery, and efferent neurons that send nerve impulses to the periphery to various executive organs. Afferent and efferent cells, with their processes, can contact each other and form a two-neuron reflex arc that performs elementary reflexes (for example, tendon reflexes of the spinal cord). But, as a rule, interneurons, or interneurons, are located in the reflex arc between the afferent and efferent neurons. Communication between different parts of the CNS is also carried out with the help of many processes of afferent, efferent and intercalary neurons of these parts, which form intracentral short and long pathways. The CNS also includes neuroglial cells, which perform a supporting function in it, and also participate in the metabolism of nerve cells. The brain and spinal cord are dressed in three meninges: dura, arachnoid and vascular, and enclosed in a protective capsule consisting of the skull and spine.

Solid - external, connective-pharyngeal, lines the internal cavity of the skull and spinal canal. The arachnoid is located under the solid - it is a thin shell with a small number of nerves and blood vessels. The choroid is fused with the brain, enters the furrows and contains many blood vessels.

Spinal cord located in the spinal canal and has the appearance of a white cord. Longitudinal grooves are located along the anterior and posterior surfaces of the spinal cord. The spinal canal passes in the center, gray matter is concentrated around it - an accumulation of a huge number of nerve cells that form the contour of a butterfly.

The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments to each other, and the spinal cord to the brain. Some pathways are called ascending or sensitive, transmitting excitation to the brain, others are descending or motor, which conduct impulses from the brain to certain segments of the spinal cord. They perform two functions - reflex and conduction. The activity of the spinal cord is under the control of the brain, which regulates spinal reflexes.

Brain human is located in the cerebral region of the skull. Its average weight is 1300-1400 g. Brain growth continues up to 20 years. It consists of 5 departments: anterior, intermediate, middle, posterior and medulla oblongata. Inside the brain there are 4 interconnected cavities - cerebral ventricles. They are filled with cerebrospinal fluid. The phylogenetically older part is the brain stem. The trunk includes the medulla oblongata, pons, midbrain and diencephalon. 12 pairs of cranial nerves lie in the brain stem. The brain stem is covered by the cerebral hemispheres.

Medulla- continuation of the spinal cord and repeats its structure; furrows lie on the anterior and posterior surfaces. It consists of white matter, where clusters of gray matter are scattered - the nuclei from which the cranial nerves originate - from the 9th to the 12th pair.

Hind brain includes the pons and cerebellum. The pons of Varolii is limited from below by the medulla oblongata, from above it passes into the legs of the brain, its lateral sections form the middle legs of the cerebellum. The cerebellum is located behind the pons and medulla oblongata. Its surface consists of gray matter (bark). Under the bark are the nuclei.

midbrain located in front of the pons, it is represented by the quadrigemina and the legs of the brain. The diencephalon occupies the highest position and lies in front of the legs of the brain. Consists of visual hillocks, supratuberous, hypothalamic region and geniculate bodies. On the periphery of the diencephalon is white matter. The forebrain consists of strongly developed hemispheres and the median part connecting them. Furrows divide the surface of the hemispheres into lobes; There are 4 lobes in each hemisphere: frontal, parietal, temporal and occipital.

The activity of the analyzers reflects the external material world in our consciousness. The activity of the cerebral cortex of humans and higher animals was defined by IP Pavlov as the higher nervous activity, which is a conditioned reflex function of the cerebral cortex.