What principle underlies the work of the nervous system? What is called a reflex? Name the links of the reflex arc, their position and functions.

The reflex principle is the basis of the work of the nervous system.

Reflex - the body's response to irritation of receptors, carried out with the participation of the central nervous system (CNS). The path along which the reflex is carried out is called the reflex arc. The reflex arc consists of the following components:

Receptor that perceives irritation;

Sensitive (centripetal) nerve pathway through which excitation is transmitted from the receptor to the central nervous system;

Nerve center - a group of intercalary neurons located in the central nervous system and transmitting nerve impulses from sensory nerve cells to motor ones;

The motor (centrifugal) nerve pathway that transmits excitation from the central nervous system to the executive organ (muscle, etc.), the activity of which changes as a result of the reflex.

The simplest reflex arcs are formed by two neurons (knee reflex) and contain sensory and motor neurons. The reflex arcs of most reflexes include not two, but a larger number of neurons: sensory, one or more intercalary and motor. Through the intercalary neurons, communication is carried out with the overlying parts of the central nervous system and information is transmitted about the adequacy of the response of the executive (working) organ to the received stimulus.

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).

1. Dominant principle 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. The dominant focus of excitation is characterized by the following properties:

* increased excitability;

* persistence of excitation (inertia), because 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. The principle of 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) (Fig. 13) 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. Therefore, the severity of such a total reflex response will be greater. This phenomenon is called the central relief. It is more often observed when weak stimuli act on the body.

3. Principle of occlusion. This principle is the opposite of spatial facilitation and it lies in the fact that two afferent inputs jointly excite a smaller group of motoneurons compared to the effects when they are activated separately, the reason for occlusion is that the afferent inputs to the convergence force are partly addressed to the same motoneurons that are inhibited when both inputs are activated simultaneously (Fig. 13). The phenomenon of occlusion is manifested in cases of application of strong afferent stimuli.

4. Feedback principle. The processes of self-regulation in the body are similar to the 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 gain - 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. Thus, during the formation of the ascending part of the AP, the depolarization of the membrane increases its sodium permeability, which, in turn, increases the depolarization of the membrane.

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

5. The principle of reciprocity (combination, conjugation, mutual exclusion). 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 (Fig. 18). Reciprocal inhibition plays an important role in the automatic coordination of motor acts,

The principle of a common final 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.

33. INHIBITION PROCESSES IN THE CENTRAL NERVOUS SYSTEM.

In the central nervous system, two main, interrelated processes are constantly functioning - excitation and inhibition.

Braking- this is an active biological process aimed at weakening, stopping or preventing the occurrence of the excitation process. The phenomenon of central inhibition, i.e., inhibition in the central nervous system, was discovered by I. M. Sechenov in 1862 in an experiment called "Sechenov's inhibition experiment." The essence of the experiment: in a frog, a crystal of table salt was applied to the cut of the optic tubercles, which led to an increase in the time of motor reflexes, i.e., to their inhibition. Reflex time is the time from the onset of irritation to the onset of a response.

Inhibition in the CNS performs two main functions. Firstly, it coordinates functions, i.e., it directs excitation along certain paths to certain nerve centers, while turning off those paths and neurons whose activity is not currently needed to obtain a specific adaptive result. The importance of this function of the inhibition process for the functioning of the organism can be observed in an experiment with the introduction of strychnine to an animal. Strychnine blocks inhibitory synapses in the CNS (mainly glycinergic) and thus eliminates the basis for the formation of the inhibition process. Under these conditions, irritation of the animal causes an uncoordinated reaction, which is based on diffuse (generalized) irradiation of excitation. In this case, adaptive activity becomes impossible. Secondly, inhibition performs a protective or protective function, protecting nerve cells from overexcitation and exhaustion under the action of superstrong and prolonged stimuli.

THEORIES OF BRAKING. NE Vvedensky (1886) showed that very frequent nerve stimulation of a neuromuscular preparation causes muscle contractions in the form of a smooth tetanus, the amplitude of which is small. N. E. Vvedensky believed that in a neuromuscular preparation with frequent irritation, a process of pessimal inhibition occurs, that is, inhibition is, as it were, a consequence of overexcitation. It has now been established that its mechanism is a prolonged, congestive depolarization of the membrane caused by an excess of the mediator (acetylcholine) released during frequent nerve stimulation. The membrane completely loses excitability due to the inactivation of sodium channels and is unable to respond to the arrival of new excitations by releasing new portions of the mediator. Thus, excitation turns into the opposite process - inhibition. Consequently, excitation and inhibition are, as it were, one and the same process, they arise in the same structures, with the participation of the same mediator. This theory of inhibition is called unitary-chemical or monistic.

Mediators on the postsynaptic membrane can cause not only depolarization (EPSP), but also hyperpolarization (TPSP). These mediators increase the permeability of the subsynaptic membrane to potassium and chloride ions, as a result of which the postsynaptic membrane becomes hyperpolarized and IPSP occurs. This theory of inhibition is called binary-chemical, according to which inhibition and excitation develop through different mechanisms, with the participation of inhibitory and excitatory mediators, respectively.

CLASSIFICATION OF CENTRAL BRAKING.

Inhibition in the CNS can be classified according to various criteria:

* according to the electrical state of the membrane - depolarization and hyperpolarization;

* in relation to the synapse - presynaptic and postsynaptic;

* according to neuronal organization - translational, lateral (lateral), recurrent, reciprocal.

Postsynaptic inhibition develops under conditions when the mediator secreted by the nerve ending changes the properties of the postsynaptic membrane in such a way that the ability of the nerve cell to generate excitation processes is suppressed. Postsynaptic inhibition can be depolarization if it is based on the process of prolonged depolarization, and hyperpolarization if it is hyperpolarization.

presynaptic inhibition due to the presence of intercalary inhibitory neurons that form axo-axonal synapses on afferent terminals that are presynaptic in relation to, for example, a motor neuron. In any case, the activation of the inhibitory interneuron, it causes depolarization of the membrane of afferent terminals, which worsens the conditions for conducting AP through them, which thus reduces the amount of mediator released by them, and, consequently, the efficiency of synaptic transmission of excitation to the motor neuron, which reduces its activity (Fig. 14) . The mediator in such axo-axonal synapses is apparently GABA, which causes an increase in the permeability of the membrane for chloride ions that leave the terminal and partially, but for a long time, depolarize it.

Forward braking due to the inclusion of inhibitory neurons along the path of excitation (Fig. 15).

Reverse braking carried out by intercalary inhibitory neurons (Renshaw cells). Impulses from motor neurons, through collaterals extending from its axon, activate the Renshaw cell, which in turn causes inhibition of the discharges of this motor neuron (Fig. 16). This inhibition is implemented due to inhibitory synapses formed by the Renshaw cell on the body of the motor neuron that activates it. Thus, a circuit with negative feedback is formed from two neurons, which makes it possible to stabilize the frequency of the motoneuron discharge and suppress its excessive activity.

Lateral (lateral) inhibition. Intercalated cells form inhibitory synapses on neighboring neurons, blocking the lateral pathways for the propagation of excitation (Fig. 17). In such cases, excitation is directed only along a strictly defined path. It is lateral inhibition that mainly provides systemic (directed) irradiation of excitation in the CNS.

Reciprocal inhibition. An example of reciprocal inhibition is the inhibition of the centers of antagonist muscles. The essence of this type of inhibition is that the excitation of the proprioreceptors of the flexor muscles simultaneously activates the motor neurons of these muscles and intercalary inhibitory neurons (Fig. 18). Excitation of the intercalary neurons leads to postsynaptic inhibition of the motor neurons of the extensor muscles.

To implement complex reactions, it is necessary to integrate the work of individual nerve centers. Most reflexes are complex, sequentially and simultaneously occurring reactions. Reflexes in the normal state of the body are strictly ordered, since there are common mechanisms for their coordination. Excitations arising in the central nervous system radiate through its centers.

Coordination is ensured by selective excitation of some centers and inhibition of others. Coordination is the unification of the reflex activity of the central nervous system into a single whole, which ensures the implementation of all body functions. The following basic principles of coordination are distinguished:

1. The principle of irradiation of excitations. The neurons of different centers are interconnected by intercalary neurons, therefore, impulses that arrive with strong and prolonged stimulation of the receptors can cause excitation not only of the neurons of the center of this reflex, but also of other neurons. For example, if one of the hind legs of a spinal frog is irritated by slightly squeezing it with tweezers, then it contracts (defensive reflex), if the irritation is increased, then both hind legs and even the front legs contract. The irradiation of excitation provides, with strong and biologically significant stimuli, the inclusion of a larger number of motor neurons in the response.

2. The principle of a common final path. Impulses coming to the CNS through different afferent fibers can converge (converge) to the same intercalary, or efferent, neurons. Sherrington called this phenomenon "the principle of a common final path". The same motor neuron can be excited by impulses coming from different receptors (visual, auditory, tactile), i.e. participate in many reflex reactions (include in various reflex arcs).

So, for example, motor neurons innervating the respiratory muscles, in addition to providing inspiration, participate in such reflex reactions as sneezing, coughing, etc. On motor neurons, as a rule, impulses from the cerebral cortex and from many subcortical centers converge (through intercalary neurons or due to direct nerve connections).

On the motoneurons of the anterior horns of the spinal cord, innervating the muscles of the limb, the fibers of the pyramidal tract, extrapyramidal pathways, from the cerebellum, the reticular formation and other structures end. The motoneuron, which provides various reflex reactions, is considered as their common final path. In which specific reflex act the motor neurons will be involved depends on the nature of the stimuli and on the functional state of the organism.

3. The principle of dominance. It was discovered by A.A. Ukhtomsky, who discovered that irritation of the afferent nerve (or cortical center), which usually leads to contraction of the muscles of the limbs during overflow in the animal intestine, causes an act of defecation. In this situation, the reflex excitation of the defecation center "suppresses, inhibits the motor centers, and the defecation center begins to respond to signals that are foreign to it.

A.A. Ukhtomsky believed that at every given moment of life, a determining (dominant) focus of excitation arises, subordinating the activity of the entire nervous system and determining the nature of the adaptive reaction. Excitations from different areas of the central nervous system converge to the dominant focus, and the ability of other centers to respond to signals coming to them is inhibited. Due to this, conditions are created for the formation of a certain reaction of the body to an irritant that has the greatest biological significance, i.e. satisfying a vital need.

Under natural conditions of existence, the dominant excitation can cover entire systems of reflexes, resulting in food, defensive, sexual and other forms of activity. The dominant excitation center has a number of properties:

1) its neurons are characterized by high excitability, which contributes to the convergence of excitations to them from other centers;

2) its neurons are able to summarize incoming excitations;

3) excitation is characterized by persistence and inertness, i.e. the ability to persist even when the stimulus that caused the formation of the dominant has ceased to act.

Despite the relative stability and inertia of excitation in the dominant focus, the activity of the central nervous system under normal conditions of existence is very dynamic and changeable. The central nervous system has the ability to restructure dominant relationships in accordance with the changing needs of the body. The doctrine of the dominant has found wide application in psychology, pedagogy, the physiology of mental and physical labor, and sports.

4. The principle of feedback. The processes occurring in the central nervous system cannot be coordinated if there is no feedback, i.e. data on the results of function management. Feedback allows you to correlate the severity of changes in system parameters with its operation. The connection of the output of the system with its input with a positive gain is called positive feedback, and with a negative gain - negative feedback. Positive feedback is mainly characteristic of pathological situations.

Negative feedback ensures the stability of the system (its ability to return to its original state after the influence of disturbing factors ceases). There are fast (nervous) and slow (humoral) feedbacks. Feedback mechanisms ensure the maintenance of all homeostasis constants. For example, maintaining a normal 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 vagus and vasomotor sympathetic nerves.

5. The principle of reciprocity. 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 limbs), and consists in the fact that the neurons of one center, being excited, inhibit the neurons of the other and vice versa.

6. The principle of subordination (subordination). The main trend in the evolution of the nervous system is manifested in the concentration of the functions of regulation and coordination in the higher parts of the central nervous system - cephalization of the functions of the nervous system. There are hierarchical relationships in the CNS - the highest center of regulation is the cerebral cortex, the basal ganglia, the middle, medulla and spinal cord obey its commands.

7. The principle of function compensation. The central nervous system has a huge compensatory ability, i.e. can restore some functions even after the destruction of a significant part of the neurons that form the nerve center (see plasticity of the nerve centers). If individual centers are damaged, their functions can be transferred to other brain structures, which is carried out with the obligatory participation of the cerebral cortex. Animals that had their cortex removed after restoration of lost functions experienced their loss again.

With local insufficiency of inhibitory mechanisms or with excessive intensification of excitation processes in one or another nerve center, a certain set of neurons begins to autonomously generate pathologically increased excitation - a generator of pathologically increased excitation is formed.

With a high generator power, a whole system of non-ironal formations functioning in a single mode arises, which reflects a qualitatively new stage in the development of the disease; rigid connections between the individual constituent elements of such a pathological system underlie its resistance to various therapeutic effects. The study of the nature of these connections allowed G.N. Kryzhanovsky to discover a new form of intracentral relations and integrative activity of the central nervous system - the determinant principle.

Its essence lies in the fact that the structure of the central nervous system, which forms a functional premise, subjugates those departments of the central nervous system to which it is addressed and forms a pathological system together with them, determining the nature of its activity. Such a system is characterized by the lack of constancy and inadequacy of functional premises, i.e. such a system is biologically negative. If, for one reason or another, the pathological system disappears, then the formation of the central nervous system, which played the main role, loses its determinant significance.

Neurophysiology of movements

The relationship of individual nerve cells and their totality form the most complex ensembles of processes that are necessary for the full life of a person, for the formation of a person as a society, defines him as a highly organized being, which puts a person on a higher level of development in relation to other animals. Thanks to the highly specific relationships of nerve cells, a person can produce complex actions and improve them. Consider below the processes necessary for the implementation of arbitrary movements.

The very act of movement begins to form in the motor area of ​​the cloak cortex. Distinguish between primary and secondary motor cortex. In the primary motor cortex (precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and limbs. It has an accurate topographic projection of the muscles of the body. In the upper parts of the precentral gyrus, the projections of the lower extremities and torso are focused, in the lower parts - the upper limbs of the head, neck and face, occupying most of the gyrus (Penfield's "motor man"). This area is characterized by increased excitability. The secondary motor zone is represented by the lateral surface of the hemisphere (field 6), it is responsible for planning and coordinating voluntary movements. It receives the bulk of the efferent impulses from the basal ganglia and the cerebellum, and is also involved in recoding information about complex movements. Irritation of the cortex of field 6 causes more complex coordinated movements (turning the head, eyes and torso to the opposite side, friendly contractions of the flexor-extensor muscles on the opposite side). In the premotor zone, there are motor centers responsible for human social functions: the center of written speech in the posterior part of the middle frontal gyrus, the center of motor speech of Broca (field 44) ​​in the posterior part of the inferior frontal gyrus, which provides speech praxis, as well as the musical motor center (field 45 ), which determines the tone of speech and the ability to sing.

In the motor cortex, a layer of large pyramidal Betz cells is better expressed than in other areas of the cortex. Motor cortex neurons receive afferent inputs through the thalamus from muscle, joint, and skin receptors, as well as from the basal ganglia and the cerebellum. Pyramidal and associated intercalary neurons are located vertically in relation to the cortex. Such adjacent neuronal complexes that perform similar functions are called functional motor columns. Pyramidal neurons of the motor column can inhibit or excite motor neurons of the stem or spinal centers, for example, innervating one muscle. Neighboring columns functionally overlap, and pyramidal neurons that regulate the activity of one muscle, as a rule, are located in several columns.

The pyramidal tracts consist of 1 million fibers of the corticospinal tract, starting from the cortex of the upper and middle third of the precentral gyrus, and 20 million fibers of the corticobulbar tract, starting from the cortex of the lower third of the precentral gyrus (projection of the face and head). The fibers of the pyramidal tract terminate on the alpha motor neurons of the motor nuclei of 3-7 and 9-12 cranial nerves (corticobulbar tract) or on the spinal motor centers (corticospinal tract). Arbitrary simple movements and complex purposeful motor programs (professional skills) are carried out through the motor cortex and pyramidal pathways, the formation of which begins in the basal ganglia and cerebellum and ends in the secondary motor zone. Most of the fibers of the motor pathway are crossed, but a small part of them go to the same side, which contributes to compensation for unilateral lesions.

The cortical extrapyramidal pathways include the corticorubral and corticoreticular pathways, starting approximately from the zones in which the pyramidal pathways begin. The fibers of the corticorubral pathway terminate on the neurons of the red nuclei of the midbrain, from which the rubrospinal pathway then begins. The fibers of the corticoreticular pathway terminate at the medial nuclei of the pontine reticular formation (beginning of the medial reticular pathway) and at the neurons of the giant cells of the reticular pathway of the medulla oblongata, from which the lateral reticulospinal pathways originate. Through these pathways, the regulation of tone and posture is carried out, providing precise movements. These extrapyramidal pathways are constituent elements of the extrapyramidal system, which also includes the cerebellum, basal ganglia, motor centers of the brain stem; it regulates the tone, posture of balance, the performance of learned motor acts, such as walking, running, speaking, writing, etc.

Assessing in general the role of various brain structures in the regulation of complex purposeful movements, it can be noted that the impulse to move is created in the limbic system, the idea of ​​movement is created in the associative zone of the cerebral hemispheres, the movement programs are in the basal ganglia, cerebellum and premotor cortex, and the execution of complex movements occur through the motor cortex, motor centers of the trunk and spinal cord.