The main principle of the functioning of the central nervous system is the process of regulation, control of physiological functions, which are aimed at maintaining the constancy of the properties and composition of the internal environment of the body. The central nervous system ensures the optimal relationship of the organism with the environment, stability, integrity, and the optimal level of vital activity of the organism.

There are two main types of regulation: humoral and nervous.

The humoral control process involves a change in the physiological activity of the body under the influence of chemicals that are delivered by the liquid media of the body. The source of information transfer is chemical substances - utilizons, metabolic products (carbon dioxide, glucose, fatty acids), informons, hormones of endocrine glands, local or tissue hormones.

The nervous process of regulation provides for the control of changes in physiological functions along nerve fibers with the help of an excitation potential under the influence of information transmission.

Characteristics:

1) is a later product of evolution;

2) provides fast handling;

3) has an exact addressee of the impact;

4) implements an economical way of regulation;

5) provides high reliability of information transmission.

In the body, the nervous and humoral mechanisms work as a single system of neurohumoral control. This is a combined form, where two control mechanisms are used simultaneously, they are interconnected and interdependent.

The nervous system is a collection of nerve cells, or neurons.

According to localization, they distinguish:

1) the central section - the brain and spinal cord;

2) peripheral - processes of nerve cells of the brain and spinal cord.

According to functional features, they distinguish:

1) somatic department that regulates motor activity;

2) vegetative, regulating the activity of internal organs, endocrine glands, blood vessels, trophic innervation of muscles and the central nervous system itself.

Functions of the nervous system:

1) integrative-coordination function. Provides the functions of various organs and physiological systems, coordinates their activities with each other;

2) ensuring close ties between the human body and the environment at the biological and social levels;

3) regulation of the level of metabolic processes in various organs and tissues, as well as in itself;

4) ensuring mental activity by the higher departments of the central nervous system.

2. Neuron. Features of the structure, meaning, types

The structural and functional unit of the nervous tissue is the nerve cell. neuron.

A neuron is a specialized cell that is able to receive, encode, transmit and store information, establish contacts with other neurons, and organize the body's response to irritation.

Functionally in a neuron, there are:

1) the receptive part (the dendrites and the membrane of the soma of the neuron);

2) integrative part (soma with axon hillock);

3) the transmitting part (axon hillock with axon).

The receiving part.

Dendrites- the main perceiving field of the neuron. The dendrite membrane is able to respond to neurotransmitters. The neuron has several branching dendrites. This is explained by the fact that a neuron as an information formation must have a large number of inputs. Through specialized contacts, information flows from one neuron to another. These contacts are called spikes.

The soma membrane of a neuron is 6 nm thick and consists of two layers of lipid molecules. The hydrophilic ends of these molecules are turned towards the aqueous phase: one layer of molecules is turned inward, the other is turned outward. The hydrophilic ends are turned towards each other - inside the membrane. Proteins are embedded in the lipid bilayer of the membrane, which perform several functions:

1) pump proteins - move ions and molecules in the cell against the concentration gradient;

2) proteins built into the channels provide selective membrane permeability;

3) receptor proteins recognize the desired molecules and fix them on the membrane;

4) enzymes facilitate the flow of a chemical reaction on the surface of the neuron.

In some cases, the same protein can function as both a receptor, an enzyme, and a pump.

integrative part.

axon hillock the exit point of an axon from a neuron.

The soma of a neuron (the body of a neuron) performs, along with an informational and trophic function, regarding its processes and synapses. The soma provides the growth of dendrites and axons. The soma of the neuron is enclosed in a multilayer membrane, which ensures the formation and distribution of the electrotonic potential to the axon hillock.

transmitting part.

axon- an outgrowth of the cytoplasm adapted to carry information that is collected by dendrites and processed in a neuron. The axon of a dendritic cell has a constant diameter and is covered with a myelin sheath, which is formed from glia; the axon has branched endings that contain mitochondria and secretory formations.

Functions of neurons:

1) generalization of the nerve impulse;

2) receipt, storage and transmission of information;

3) the ability to summarize excitatory and inhibitory signals (integrative function).

Types of neurons:

1) by localization:

a) central (brain and spinal cord);

b) peripheral (cerebral ganglia, cranial nerves);

2) depending on the function:

a) afferent (sensitive), carrying information from receptors in the central nervous system;

b) intercalary (connector), in the elementary case, providing a connection between the afferent and efferent neurons;

c) efferent:

- motor - anterior horns of the spinal cord;

- secretory - lateral horns of the spinal cord;

3) depending on the functions:

a) exciting;

b) inhibitory;

4) depending on the biochemical characteristics, on the nature of the mediator;

5) depending on the quality of the stimulus that is perceived by the neuron:

a) monomodal;

b) polymodal.

3. Reflex arc, its components, types, functions

The activity of the body is a natural reflex reaction to a stimulus. Reflex- the reaction of the body to irritation of receptors, which is carried out with the participation of the central nervous system. The structural basis of the reflex is the reflex arc.

reflex arc- a chain of nerve cells connected in series, which ensures the implementation of a reaction, a response to irritation.

The reflex arc consists of six components: receptors, afferent (sensory) pathway, reflex center, efferent (motor, secretory) pathway, effector (working organ), feedback.

Reflex arcs can be of two types:

1) simple - monosynaptic reflex arcs (reflex arc of the tendon reflex), consisting of 2 neurons (receptor (afferent) and effector), there is 1 synapse between them;

2) complex - polysynaptic reflex arcs. They include 3 neurons (there may be more) - receptor, one or more intercalary and effector.

The idea of ​​a reflex arc as an expedient response of the body dictates the need to supplement the reflex arc with one more link - a feedback loop. This component establishes a link between the realized result of the reflex reaction and the nerve center that issues executive commands. With the help of this component, the open reflex arc is transformed into a closed one.

Features of a simple monosynaptic reflex arc:

1) geographically close receptor and effector;

2) the reflex arc is two-neuron, monosynaptic;

3) nerve fibers of group A? (70-120 m/s);

4) short reflex time;

5) muscles that contract as a single muscle contraction.

Features of a complex monosynaptic reflex arc:

1) territorially separated receptor and effector;

2) the receptor arc is three-neuronal (maybe more neurons);

3) the presence of nerve fibers of groups C and B;

4) muscle contraction by the type of tetanus.

Features of the autonomic reflex:

1) the intercalary neuron is located in the lateral horns;

2) from the lateral horns begins the preganglionic nerve path, after the ganglion - postganglionic;

3) the efferent path of the reflex of the autonomic neural arch is interrupted by the autonomic ganglion, in which the efferent neuron lies.

The difference between the sympathetic neural arch and the parasympathetic one: in the sympathetic neural arch, the preganglionic path is short, since the autonomic ganglion lies closer to the spinal cord, and the postganglionic path is long.

In the parasympathetic arch, the opposite is true: the preganglionic path is long, since the ganglion lies close to the organ or in the organ itself, and the postganglionic path is short.

4. Functional systems of the body

Functional system- temporary functional association of the nerve centers of various organs and systems of the body to achieve the final beneficial result.

A useful result is a self-forming factor of the nervous system. The result of the action is a vital adaptive indicator that is necessary for the normal functioning of the body.

There are several groups of end useful results:

1) metabolic - a consequence of metabolic processes at the molecular level, which create substances and end products necessary for life;

2) homeostatic - the constancy of indicators of the state and composition of the environment of the body;

3) behavioral - the result of a biological need (sexual, food, drinking);

4) social - satisfaction of social and spiritual needs.

The functional system includes various organs and systems, each of which takes an active part in achieving a useful result.

The functional system, according to P.K. Anokhin, includes five main components:

1) a useful adaptive result - something for which a functional system is created;

2) control apparatus (result acceptor) - a group of nerve cells in which a model of the future result is formed;

3) reverse afferentation (supplies information from the receptor to the central link of the functional system) - secondary afferent nerve impulses that go to the acceptor of the result of the action to evaluate the final result;

4) control apparatus (central link) - functional association of nerve centers with the endocrine system;

5) executive components (reaction apparatus) are the organs and physiological systems of the body (vegetative, endocrine, somatic). Consists of four components:

a) internal organs;

b) endocrine glands;

c) skeletal muscles;

d) behavioral responses.

Functional system properties:

1) dynamism. The functional system may include additional organs and systems, depending on the complexity of the situation;

2) the ability to self-regulation. When the controlled value or the final useful result deviates from the optimal value, a series of spontaneous complex reactions occur, which returns the indicators to the optimal level. Self-regulation is carried out in the presence of feedback.

Several functional systems work simultaneously in the body. They are in continuous interaction, which is subject to certain principles:

1) the principle of the system of genesis. Selective maturation and evolution of functional systems take place (functional systems of blood circulation, respiration, nutrition, mature and develop earlier than others);

2) the principle of multiply connected interaction. There is a generalization of the activity of various functional systems, aimed at achieving a multicomponent result (parameters of homeostasis);

3) the principle of hierarchy. Functional systems are lined up in a certain row in accordance with their significance (functional tissue integrity system, functional nutrition system, functional reproduction system, etc.);

4) the principle of consistent dynamic interaction. There is a clear sequence of changing the activity of one functional system of another.

5. Coordinating activity of the CNS

Coordination activity (CA) of the CNS is a coordinated work of CNS neurons based on the interaction of neurons with each other.

CD functions:

1) provides a clear performance of certain functions, reflexes;

2) ensures the consistent inclusion in the work of various nerve centers to ensure complex forms of activity;

3) ensures the coordinated work of various nerve centers (during the act of swallowing, the breath is held at the moment of swallowing; when the swallowing center is excited, the respiratory center is inhibited).

Basic principles of CNS CD and their neural mechanisms.

1. The principle of irradiation (spread). When small groups of neurons are excited, the excitation spreads to a significant number of neurons. Irradiation is explained:

1) the presence of branched endings of axons and dendrites, due to branching, impulses propagate to a large number of neurons;

2) the presence of intercalary neurons in the CNS, which ensure the transmission of impulses from cell to cell. Irradiation has a boundary, which is provided by an inhibitory neuron.

2. The principle of convergence. When a large number of neurons are excited, the excitation can converge to one group of nerve cells.

3. The principle of reciprocity - the coordinated work of the nerve centers, especially in opposite reflexes (flexion, extension, etc.).

4. The principle of dominance. Dominant- the dominant focus of excitation in the central nervous system at the moment. This is a focus of persistent, unwavering, non-spreading excitation. It has certain properties: it suppresses the activity of other nerve centers, has increased excitability, attracts nerve impulses from other foci, summarizes nerve impulses. There are two types of dominant foci: exogenous origin (caused by environmental factors) and endogenous (caused by internal environmental factors). The dominant underlies the formation of a conditioned reflex.

5. The principle of feedback. Feedback - the flow of impulses to the nervous system, which informs the central nervous system about how the response is carried out, whether it is sufficient or not. There are two types of feedback:

1) positive feedback, causing an increase in the response from the nervous system. Underlies a vicious circle that leads to the development of diseases;

2) negative feedback, which reduces the activity of CNS neurons and the response. Underlies self-regulation.

6. The principle of subordination. In the CNS, there is a certain subordination of departments to each other, the highest department is the cerebral cortex.

7. The principle of interaction between the processes of excitation and inhibition. The central nervous system coordinates the processes of excitation and inhibition:

both processes are capable of convergence, the process of excitation and, to a lesser extent, inhibition, are capable of irradiation. Inhibition and excitation are connected by inductive relationships. The process of excitation induces inhibition, and vice versa. There are two types of induction:

1) consistent. The process of excitation and inhibition replace each other in time;

2) mutual. At the same time, there are two processes - excitation and inhibition. Mutual induction is carried out by positive and negative mutual induction: if inhibition occurs in a group of neurons, then foci of excitation arise around it (positive mutual induction), and vice versa.

According to IP Pavlov's definition, excitation and inhibition are two sides of the same process. The coordination activity of the CNS provides a clear interaction between individual nerve cells and individual groups of nerve cells. There are three levels of integration.

The first level is provided due to the fact that impulses from different neurons can converge on the body of one neuron, as a result, either summation or a decrease in excitation occurs.

The second level provides interactions between separate groups of cells.

The third level is provided by the cells of the cerebral cortex, which contribute to a more perfect level of adaptation of the activity of the central nervous system to the needs of the body.

6. Types of inhibition, interaction of the processes of excitation and inhibition in the central nervous system. Experience of I. M. Sechenov

Braking- an active process that occurs under the action of stimuli on the tissue, manifests itself in the suppression of another excitation, there is no functional administration of the tissue.

Inhibition can only develop in the form of a local response.

There are two types of braking:

1) primary. For its occurrence, the presence of special inhibitory neurons is necessary. Inhibition occurs primarily without prior excitation under the influence of an inhibitory mediator. There are two types of primary inhibition:

a) presynaptic in the axo-axonal synapse;

b) postsynaptic in the axodendric synapse.

2) secondary. It does not require special inhibitory structures, it arises as a result of a change in the functional activity of ordinary excitable structures, it is always associated with the process of excitation. Types of secondary braking:

a) beyond, arising from a large flow of information entering the cell. The flow of information lies outside the neuron's performance;

b) pessimal, arising at a high frequency of irritation;

c) parabiotic, arising from strong and long-acting irritation;

d) inhibition following excitation, resulting from a decrease in the functional state of neurons after excitation;

e) braking according to the principle of negative induction;

f) inhibition of conditioned reflexes.

The processes of excitation and inhibition are closely related, occur simultaneously and are different manifestations of a single process. The foci of excitation and inhibition are mobile, cover larger or smaller areas of neuronal populations, and may be more or less pronounced. Excitation will certainly be replaced by inhibition, and vice versa, i.e., there are inductive relations between inhibition and excitation.

Inhibition underlies the coordination of movements, protects the central neurons from overexcitation. Inhibition in the central nervous system can occur when nerve impulses of various strengths from several stimuli simultaneously enter the spinal cord. Stronger stimulation inhibits the reflexes that should have come in response to weaker ones.

In 1862, I. M. Sechenov discovered the phenomenon of central inhibition. He proved in his experiment that irritation of the frog's optic tubercles with a sodium chloride crystal (the large hemispheres of the brain were removed) causes inhibition of spinal cord reflexes. After elimination of the stimulus, the reflex activity of the spinal cord was restored. The result of this experiment allowed I. M. Secheny to conclude that in the central nervous system, along with the process of excitation, a process of inhibition develops, which is capable of inhibiting the reflex acts of the body. N. E. Vvedensky suggested that the principle of negative induction underlies the phenomenon of inhibition: a more excitable section in the central nervous system inhibits the activity of less excitable sections.

The modern interpretation of the experience of I. M. Sechenov (I. M. Sechenov irritated the reticular formation of the brain stem): excitation of the reticular formation increases the activity of inhibitory neurons of the spinal cord - Renshaw cells, which leads to inhibition of β-motor neurons of the spinal cord and inhibits the reflex activity of the spinal cord.

7. Methods for studying the central nervous system

There are two large groups of methods for studying the CNS:

1) an experimental method that is carried out on animals;

2) a clinical method that is applicable to humans.

To the number experimental methods Classical physiology includes methods aimed at activating or suppressing the studied nerve formation. These include:

1) the method of transverse transection of the central nervous system at various levels;

2) method of extirpation (removal of various departments, denervation of the organ);

3) the method of irritation by activation (adequate irritation - irritation by an electrical impulse similar to a nervous one; inadequate irritation - irritation by chemical compounds, graded irritation by electric current) or suppression (blocking the transmission of excitation under the influence of cold, chemical agents, direct current);

4) observation (one of the oldest method of studying the functioning of the central nervous system that has not lost its significance. It can be used independently, more often used in combination with other methods).

Experimental methods are often combined with each other when conducting an experiment.

clinical method aimed at studying the physiological state of the central nervous system in humans. It includes the following methods:

1) observation;

2) a method for recording and analyzing the electrical potentials of the brain (electro-, pneumo-, magnetoencephalography);

3) radioisotope method (explores neurohumoral regulatory systems);

4) conditioned reflex method (studies the functions of the cerebral cortex in the mechanism of learning, development of adaptive behavior);

5) the method of questioning (assesses the integrative functions of the cerebral cortex);

6) modeling method (mathematical modeling, physical, etc.). A model is an artificially created mechanism that has a certain functional similarity with the mechanism of the human body under study;

7) cybernetic method (studies the processes of control and communication in the nervous system). It is aimed at studying organization (systemic properties of the nervous system at various levels), management (selection and implementation of the influences necessary to ensure the operation of an organ or system), information activity (the ability to perceive and process information - an impulse in order to adapt the body to environmental changes).

The functioning of the nervous system is based on reflex activity. Reflex (from lat. Reflexio - I reflect) is the body's response to external or internal irritation with the mandatory participation of the nervous system.

The reflex principle of the functioning of the nervous system

A reflex is the body's response to an external or internal stimulus. Reflexes are divided into:

1. unconditioned reflexes: innate reactions of the body to stimuli carried out with the participation of the spinal cord or brain stem;
2. conditioned reflexes: temporary reactions of the body acquired on the basis of unconditioned reflexes, carried out with the obligatory participation of the cerebral cortex, which form the basis of higher nervous activity.

The morphological basis of the reflex is a reflex arc, represented by a chain of neurons that provide the perception of irritation, the transformation of the energy of irritation into a nerve impulse, the conduction of a nerve impulse to the nerve centers, the processing of incoming information and the implementation of a response.

Reflex activity presupposes the presence of a mechanism consisting of three main elements connected in series:

1. Receptors that perceive irritation and transform it into a nerve impulse; usually receptors are represented by various sensitive nerve endings in organs;

2. Effectors, which result in the effect of stimulating receptors in the form of a specific reaction; effectors include all internal organs, blood vessels and muscles;

3. chains connected in series neurons, which, by directionally transmitting excitation in the form of nerve impulses, ensure the coordination of the activity of effectors depending on the stimulation of the receptors.

A chain of neurons connected in series with each other forms reflex arc, which constitutes the material substratum of the reflex.

Functionally, the neurons that form the reflex arc can be divided into:

1. afferent (sensory) neurons that perceive stimulation and transmit it to other neurons. Sensory neurons are always located outside the central nervous system in the sensory ganglia of the spinal and cranial nerves. Their dendrites form sensitive nerve endings in the organs.

2. efferent (motor, motor) neurons, or motor neurons, transmit excitation to effectors (for example, muscles or blood vessels);

3. interneurons (interneurons) interconnect afferent and efferent neurons and thereby close the reflex connection.

The simplest reflex arc consists of two neurons - afferent and efferent. Three neurons are involved in a more complex reflex arc: afferent, efferent and intercalary. The maximum number of neurons involved in the reflex response of the nervous system is limited, especially in cases where different parts of the brain and spinal cord are involved in the reflex act. At present, the basis of reflex activity is taken reflex ring. The classical reflex arc is supplemented by the fourth link - the reverse afferentation from the effectors. All neurons involved in reflex activity have a strict localization in the nervous system.

Nerve center

Anatomically, the center of the nervous system is a group of adjacent neurons that are closely related structurally and functionally and perform a common function in reflex regulation. In the nerve center, perception, analysis of incoming information and its transmission to other nerve centers or effectors take place. Therefore, each nerve center has its own system of afferent fibers, through which it is brought into an active state, and a system of efferent connections that conduct nervous excitation to other nerve centers or effectors. Distinguish peripheral nerve centers, represented by nodes ( ganglia ): sensitive and vegetative. In the central nervous system there are nuclear centers (nuclei)- local clusters of neurons, and cortical centers - extensive settlement of neurons on the surface of the brain.

Blood supply to the brain and spinal cord

I. Blood supply to the brain carried out by branches of the left and right internal carotid arteries and branches of the vertebral arteries.

internal carotid artery, entering the cranial cavity, it divides into the ophthalmic artery and the anterior and middle cerebral arteries. Anterior cerebral artery nourishes mainly the frontal lobe of the brain, middle cerebral artery - parietal and temporal lobes, and ophthalmic artery supplies blood to the eyeball. The anterior cerebral arteries (right and left) are connected by a transverse anastomosis - the anterior communicating artery.

Vertebral arteries (right and left) in the region of the brain stem unite and form an unpaired basilar artery, feeding the cerebellum and other parts of the trunk, and two posterior cerebral arteries supplying blood to the occipital lobes of the brain. Each of the posterior cerebral arteries is connected to the middle cerebral artery of its side by means of the posterior communicating artery.

Thus, on the basis of the brain, an arterial circle of the cerebrum is formed.

Smaller ramifications of blood vessels in the pia mater

reach the brain, penetrate into its substance, where they are divided into numerous capillaries. From the capillaries, blood is collected in small, and then large venous vessels. Blood from the brain flows into the sinuses of the dura mater. Blood flows from the sinuses through the jugular foramina at the base of the skull into the internal jugular veins.

2. Blood supply to the spinal cord through the anterior and posterior spinal arteries. The outflow of venous blood goes through the veins of the same name to the internal vertebral plexus, located along the entire length of the spinal canal outside of the hard shell of the spinal cord. From the internal vertebral plexus, blood flows into the veins that run along the spinal column, and from them into the inferior and superior vena cava.

Liquor system of the brain

Inside the bone cavities, the brain and spinal cord are in suspension and are washed from all sides by cerebrospinal fluid - liquor. Liquor protects the brain from mechanical influences, ensures the constancy of intracranial pressure, is directly involved in the transport of nutrients from the blood to the brain tissues. Cerebrospinal fluid is produced by the choroid plexuses of the ventricles of the brain. CSF circulation through the ventricles is carried out according to the following scheme: from the lateral ventricles, the fluid enters through the foramen of Monro into the third ventricle, and then through the Sylvian aqueduct into the fourth ventricle. From it, the cerebrospinal fluid passes through the holes of Magendie and Luschka into the subarachnoid space. The outflow of cerebrospinal fluid into the venous sinuses occurs through the granulation of the arachnoid - pachyon granulations.

Between neurons and blood in the brain and spinal cord there is a barrier called blood-brain, which ensures the selective flow of substances from the blood to nerve cells. This barrier performs a protective function, as it ensures the constancy of the physico-chemical properties of the liquor.

Picks

Neurotransmitters (neurotransmitters, mediators) are biologically active chemicals through which an electrical impulse is transmitted from a nerve cell through the synaptic space between neurons. The nerve impulse entering the presynaptic ending causes the mediator to be released into the synaptic cleft. The mediator molecules react with specific receptor proteins of the cell membrane, initiating a chain of biochemical reactions that cause a change in the transmembrane current of ions, which leads to membrane depolarization and the emergence of an action potential.

Until the 1950s, mediators included two groups of low molecular weight compounds: amines (acetylcholine, adrenaline, norepinephrine, serotonin, dopamine) and amino acids (gamma-aminobutyric acid, glutamate, aspartate, glycine). Later, it was shown that neuropeptides constitute a specific group of mediators, which can also act as neuromodulators (substances that change the magnitude of a neuron's response to a stimulus). It is now known that a neuron can synthesize and release several neurotransmitters.

In addition, there are special nerve cells in the nervous system - neurosecretory, which provide a link between the central nervous system and the endocrine system. These cells have a typical neuron structural and functional organization. They are distinguished from a neuron by a specific function - neurosecretory, which is associated with the secretion of biologically active substances. Axons of neurosecretory cells have numerous extensions (Hering's bodies), in which neurosecretion temporarily accumulates. Within the brain, these axons are typically devoid of myelin sheath. One of the main functions of neurosecretory cells is the synthesis of proteins and polypeptides and their further secretion. In this regard, in these cells, the protein-synthesizing apparatus is extremely developed - the granular endoplasmic reticulum, the Golgi complex, and the lysosomal apparatus. By the number of neurosecretory granules in a cell, one can judge its activity.



1. Principle dominants was formulated by A. A. Ukhtomsky as the basic principle of the work of nerve centers. According to this principle, the activity of the nervous system is characterized by the presence in the central nervous system of the dominant (dominant) foci of excitation in a given period of time, in the nerve centers, which determine the direction and nature of body functions during this period.

Dominant focus excitation is characterized by the following properties:

Increased excitability;

Persistence of excitation (inertness), since it is difficult to suppress other excitation;

The ability to summation of subdominant excitations;

The ability to inhibit subdominant foci of excitation in functionally different nerve centers.

2. Principle spatial relief

It manifests itself in the fact that the total response of the organism with the simultaneous action of two relatively weak stimuli will be greater than the sum of the responses obtained with their separate action. The reason for the relief is due to the fact that the axon of an afferent neuron in the CNS synapses with a group of nerve cells, in which a central (threshold) zone and a peripheral (subthreshold) "border" are isolated. Neurons located in the central zone receive from each afferent neuron a sufficient number of synaptic endings (for example, 2 each) to form an action potential. The neuron of the subthreshold zone receives from the same neurons a smaller number of endings (1 each), so their afferent impulses will be insufficient to cause the generation of action potentials in the "border" neurons, and only subthreshold excitation occurs. As a result, with separate stimulation of afferent neurons 1 and 2, reflex reactions occur, the total severity of which is determined only by the neurons of the central zone (3). But with simultaneous stimulation of afferent neurons, action potentials are also generated by neurons of the subthreshold zone due to the overlap of the border zone of two closely spaced neurons. Therefore, the severity of such a total reflex response will be greater. This phenomenon has been named central relief. It is more often observed when weak stimuli act on the body.

3.Principle occlusion. This principle is the opposite of spatial facilitation, and it consists in the fact that two afferent inputs jointly excite a smaller group of motor neurons compared to the effects when they are activated separately. The reason for occlusion is that the afferent inputs, due to convergence, are partly addressed to the same motor neurons (overlapping of neurons in the threshold zone occurs). The phenomenon of occlusion is manifested in cases of application of strong afferent stimuli.

4. Principle feedback.

The processes of self-regulation in the body are similar to technical ones, which involve automatic regulation of the process using feedback. The presence of feedback allows you to correlate the severity of changes in the parameters of the system with its work as a whole. The connection of the output of the system with its input with a positive gain is called positive feedback, and with a negative coefficient - negative feedback. In biological systems, positive feedback is realized mainly in pathological situations. Negative feedback improves the stability of the system, i.e., its ability to return to its original state after the influence of disturbing factors ceases.

Feedback can be classified according to various criteria. For example, according to the speed of action - fast (nervous) and slow (humoral) etc.

Many examples of feedback effects can be cited. For example, in the nervous system, the activity of motor neurons is regulated in this way. The essence of the process lies in the fact that excitation impulses propagating along the axons of motor neurons reach not only the muscles, but also specialized intermediate neurons (Renshaw cells), the excitation of which inhibits the activity of motor neurons. This effect is known as the rebound inhibition process.

An example of positive feedback is the process of generating an action potential. So, during the formation of the ascending part of the AP, the depolarization of the membrane increases its sodium permeability, which, in turn, by increasing the sodium current, increases the membrane depolarization.

The importance of feedback mechanisms in maintaining homeostasis is great. For example, maintaining a constant level of blood pressure is carried out by changing the impulse activity of the baroreceptors of the vascular reflexogenic zones, which change the tone of the vasomotor sympathetic nerves and thus normalize blood pressure.

5. Principle reciprocity (combinations, conjugations, mutual exclusions).

It reflects the nature of the relationship between the centers responsible for the implementation of opposite functions (inhalation and exhalation, flexion and extension of the limb, etc.). For example, activation of the proprioreceptors of the flexor muscle simultaneously excites the motor neurons of the flexor muscle and inhibits the motor neurons of the extensor muscle through intercalary inhibitory neurons. Reciprocal inhibition plays an important role in the automatic coordination of motor acts.

6. Principle common end path.

The effector neurons of the central nervous system (primarily the motor neurons of the spinal cord), being the final ones in the chain consisting of afferent, intermediate and effector neurons, can be involved in the implementation of various body reactions by excitations coming to them from a large number of afferent and intermediate neurons, for which they are the final path (by way from the CNS to the effector). For example, on the motoneurons of the anterior horns of the spinal cord, which innervate the muscles of the limb, the fibers of afferent neurons, neurons of the pyramidal tract and extrapyramidal system (nuclei of the cerebellum, reticular formation and many other structures) terminate. Therefore, these motor neurons, which provide the reflex activity of the limb, are considered as the final path for the general implementation of many nerve influences on the limb. This principle is based on the phenomenon convergence

7. Principleinduction or modular organization - around the excited central neurons of the ensemble, a zone of inhibited neurons appears - the inhibitory edging.

8. Principlestrength - if signals from different reflexogenic zones simultaneously arrive at one nerve center (according to the principle of a common final path), then the center reacts to a stronger excitation.

9. Principlesubordination or subordination - the lower divisions of the central nervous system are subordinate to the overlying ones. Moreover, ascending influences are predominantly excitatory, while descending influences are both excitatory and inhibitory (more often inhibitory).