Types of autonomic reflexes. Autonomic reflexes, features of the reflex arc, classification and clinical significance Classification of autonomic reflexes

Autonomic reflexes are caused by stimulation of both inter and exteroceptors. Among the numerous and varied autonomic reflexes, viscero-visceral, viscerodermal, dermatovisceral, visceromotor and motor-visceral are distinguished.

Viscero-visceral reflexes are caused by irritation of interoreceptors (visceroreceptors) located in the internal organs. They are playing important role V functional interaction internal organs and their self-regulation. These reflexes include viscerocardial, cardiocardiac, gastrohepatic, etc. Some patients with damage to the stomach experience gastrocardial syndrome, one of the manifestations of which is disruption of the heart, up to the appearance of angina attacks caused by insufficient coronary circulation.

Viscerodermal reflexes occur when receptors are stimulated visceral organs and are manifested by impaired skin sensitivity, sweating, and skin elasticity in limited areas of the skin surface (dermatome). Such reflexes can be observed in the clinic. Thus, with diseases of the internal organs, tactile (hyperesthesia) and pain (hyperalgesia) sensitivity increases in limited areas of the skin. It is possible that painful and non-painful cutaneous afferent fibers and visceral afferents belonging to a specific segment of the spinal cord are converted on the same neurons of the sympothalamic pathway.

Dermatovisceral reflexes manifest themselves in the fact that irritation of certain areas of the skin is accompanied by vascular reactions and dysfunction of certain internal organs. This is the basis for the use of a number of therapeutic procedures (physiotherapy, reflexology). Thus, damage to the thermoreceptors of the skin (by heating or cooling) through the sympathetic centers leads to redness of the skin, inhibition of the activity of internal organs that are innervated from the segments of the same name.

Visceromotor and motor-visceral reflexes. With the manifestation of segmental organization autonomic innervation internal organs are also associated with visceromotor reflexes, in which excitation of receptors of internal organs leads to a reduction or inhibition of the current activity of skeletal muscles.

There are “corrective” and “trigger” influences from the receptor fields of internal organs on skeletal muscles. The former lead to changes in skeletal muscle contractions, which occur under the influence of other afferent stimuli, enhancing or suppressing them. The latter independently activate contractions of skeletal muscles. Both types of influences are associated with an increase in signals received by the afferent pathways of the autonomic reflex arc. Visceromotor reflexes are often observed in diseases of internal organs. For example, with cholecystitis or appendicitis, muscle tension occurs in the stalemate area. process. Protective visceromotor reflexes also include the so-called forced postures that a person takes in case of diseases of the internal organs (for example, flexion and adduction lower limbs to the stomach).

6. Levels of regulation of autonomic functions. The hypothalamus as the highest subcortical center for the regulation of autonomic functions.

In the system of regulation of vegetative functions, there are several levels that interact with each other and subordination is observed lower levels higher-lying departments.

Coordination of the activities of all three parts of the autonomic nervous system is carried out by segmental and suprasegmental centers (apparatuses) with the participation of the cerebral cortex.

Segmental centers due to the peculiarities of their organization and patterns of functioning, they are truly autonomous. In the central nervous system they are located in the spinal cord and in the brain stem (separate nuclei cranial nerves), and on the periphery they form a complex system of plexuses, ganglia, and fibers.

Suprasegmental centers located in the brain mainly at the limbic-reticular level. These integrative centers provide holistic forms of behavior, adaptation to changing conditions of the external and internal environment.

All these complex mechanisms regulation of the activity of visceral functions are conditionally united by a multi-story hierarchical structure. Its basic (first) level is intraorgan reflexes. The second structural level is the extramural paravertebral ganglia of the mesenteric and celiac plexuses. Both first levels have pronounced autonomy. The third structural level is represented by the centers of the spinal cord and brain stem. The highest level of regulation (fourth) is represented by the hypothalamus, reticular formation, limbic system and cerebellum. The new KBP closes the hierarchy pyramid.

Spinal level. At the level of the last cervical and two upper thoracic segments of the spinal cord is the spinociliary center. Its fibers end on the muscles of the eye. When these neurons are stimulated, dilation of the pupil (mydriasis), widening of the palpebral fissure and protrusion of the eye (exophthalmos) are observed. When this department is damaged, Bernard-Horner syndrome is observed - constriction of the pupil (miosis), narrowing of the palpebral fissure and retraction of the eye (endophthalmos).

The five upper segments of the thoracic spinal cord send impulses to the heart and bronchi. Damage to individual segments of the thoracic and upper lumbar causes the disappearance of vascular tone and sweating.

IN sacral region the centers with the participation of which the reflexes of the genitourinary system and defecation are regulated are localized. If the spinal cord is ruptured above the sacral region, these functions may disappear.

In the medulla oblongata The vasomotor center is located, which coordinates the activity of the sympathetic nerves located in the thoracolumbar spinal cord. Also in the medulla oblongata there are centers that inhibit the functions of the heart and activate the gastrointestinal glands, regulating the acts of sucking, swallowing, sneezing, coughing, vomiting, and lacrimation. These influences are transmitted to the executive organs through the fibers of the vagus, glossopharyngeal and facial nerves.

In the midbrain center localized pupillary reflex and accommodation of the eye. These departments are subordinate to the higher-lying structures.

Hypothalamus is the highest center for the regulation of vegetative functions, which are responsible for the state of the internal environment of the body. It is an important integrative center of autonomic, somatic and endocrine functions.
Hypothalamus - central department diencephalon. It lies ventral to the thalamus. The inferior border of the thalamus is midbrain, and the top one is the terminal plate, the anterior commissure and the optic chiasm. It has about 48 pairs of nuclei. The following areas are distinguished in the hypothalamus: 1) preoptic, 2) anterior group, 3) middle group, 4) outer group, 5) back group. Among the nuclei, specific and nonspecific ones are distinguished. Specific nuclei are connected to the pituitary gland and are capable of neurocrinia, i.e. synthesis and release of a number of hormones.
The nuclei of the hypothalamus are neither sympathetic nor parasympathetic, although it is generally accepted that in the posterior nuclei of the hypothalamus there are groups of neurons connected primarily to the sympathetic system, and in its anterior nuclei there are neurons that regulate functions parasympathetic system. The hypothalamus regulates the functions of both parts of the autonomic nervous system depending on the nature and level of afferentation entering its nuclei. It forms two-way (afferent and efferent) connections with various parts of the brain - upper sections brain stem, central gray matter of the midbrain, with the structures of the limbic system of the thalamus, reticular formation, subcortical nuclei and cortex. Afferent signals enter the hypothalamus from the surface of the body and internal organs, as well as from some parts of the brain. In the medial region of the hypothalamus there are special neurons (osmo-, gluco-, thermoreceptors) that control important parameters of the blood (water-electrolyte composition of plasma, blood temperature, etc.) and cerebrospinal fluid, that is, they “monitor” the state of the internal environment of the body. Through neural mechanisms, the medial portion of the hypothalamus controls the activity of the neurohypophysis, and through humoral mechanisms, the adenohypophysis.
The hypothalamus regulates water-electrolyte metabolism, body temperature, functions endocrine glands, puberty, activity of the cardiovascular, respiratory systems, digestive organs, kidneys. It is involved in the formation of food and sexual protection, in the regulation of the sleep-vigor cycle, etc. Therefore, any effect on the hypothalamus is accompanied by a complex of reactions from many body systems, which is expressed in visceral, somatic and mental effects.
In case of damage to the hypothalamus (tumors, traumatic or inflammatory lesions), disorders of energy and water balance, thermoregulation, and functions are observed. cardiovascular system, digestive organs, endocrine disorders, emotional reactions.
The autonomic functions of the body are significantly influenced by the limbic structures of the brain.

The structure of the hypothalamus . The hypothalamus belongs to the phylogenetically ancient formations of the brain and is already well developed in lower vertebrates. It forms the floor of the third ventricle and lies between the chiasm optic nerves and the posterior edge of the mammillary bodies. The hypothalamus includes the gray tubercle, the median eminence, the infundibulum and the posterior or neural lobe of the pituitary gland. Anteriorly, it borders on the preoptic area, which some authors also include in the hypothalamus system.

PHYSIOLOGY OF HIGHER NERVOUS ACTIVITY

1. Conditioned reflex as a form of human adaptation to changing conditions of existence. Differences between conditioned and unconditioned reflexes. Patterns of formation and manifestation of conditioned reflexes.

Adaptation of animals and humans to changing conditions of existence in external environment is ensured by the activity of the nervous system and is realized through reflex activity. In the process of evolution, hereditarily fixed reactions (unconditioned reflexes) arose that combine and coordinate the functions of various organs and carry out adaptation of the body. In humans and higher animals, in the process of individual life, qualitatively new reflex reactions arise, which I. P. Pavlov called conditioned reflexes, considering them the most perfect form devices.

While relatively simple forms of nervous activity determine the reflex regulation of homeostasis and autonomic functions of the body, higher nervous activity (HNA) provides complex individual forms of behavior in changing living conditions. GNI is realized due to the dominant influence of the cortex on all underlying structures of the central nervous system. The main processes that dynamically replace each other in the central nervous system are the processes of excitation and inhibition. Depending on their ratio, strength and localization, the control influences of the cortex are built. The functional unit of the GNI is the conditioned reflex.

Reflexes are conditioned and unconditioned. An unconditioned reflex is a reflex that is inherited and passed on from generation to generation. In humans, by the time of birth, the almost reflex arc of unconditioned reflexes is fully formed, with the exception of sexual reflexes. Unconditioned reflexes are species-specific, that is, they are characteristic of individuals of a given species.

Conditioned reflexes (CR) are an individually acquired reaction of the body to a previously indifferent stimulus (stimulus is any material agent, external or internal, conscious or unconscious, acting as a condition for subsequent states of the body. Signal stimulus (also indifferent) is a stimulus that has not previously caused corresponding reaction, but under certain conditions of formation of a conditioned reflex, which begins to cause it), reproducing unconditioned reflex. SDs are formed throughout life and are associated with the accumulation of life experience. They are individual for each person or animal. Able to fade away if not reinforced. Extinguished conditioned reflexes do not disappear completely, that is, they are capable of recovery.

General properties of conditioned reflexes. Despite certain differences, conditioned reflexes are characterized by the following general properties (features):

· All conditioned reflexes represent one of the forms of adaptive reactions of the body to changing environmental conditions.

· SDs are acquired and canceled during the individual life of each individual.

· All UR are formed with the participation of the central nervous system.

· SD are formed on the basis of unconditioned reflexes; Without reinforcement, conditioned reflexes are weakened and suppressed over time.

All types of conditioned reflex activity are of a warning signal nature. That is, they precede and prevent the subsequent occurrence of BD. They prepare the body for any biologically targeted activity. UR is a reaction to a future event. SDs are formed due to the plasticity of the NS.

Biological role SD is to expand the range of adaptive capabilities of the body. SD complements BR and allows subtle and flexible adaptation to a wide variety of conditions environment.

Differences between conditioned reflexes and unconditioned ones

1. Unconditioned reactions are innate, hereditary reactions; they are formed on the basis of hereditary factors and most of them begin to function immediately after birth. Conditioned reflexes are acquired reactions in the process of individual life.

2. Unconditioned reflexes are species-specific, that is, these reflexes are characteristic of all representatives of a given species. Conditioned reflexes are individual; some animals may develop certain conditioned reflexes, while others may develop others.

3. Unconditioned reflexes are constant; they persist throughout the life of the organism. Conditioned reflexes are not constant; they can arise, become established and disappear.

4. Unconditioned reflexes are carried out due to the lower parts of the central nervous system (subcortical nuclei, brain stem, spinal cord). Conditioned reflexes are primarily a function of the higher parts of the central nervous system - the cerebral cortex.

5. Unconditioned reflexes are always carried out in response to adequate stimulation acting on a certain receptive field, i.e. they are structurally fixed. Conditioned reflexes can be formed to any stimuli, from any receptive field.

6. Unconditioned reflexes are reactions to direct irritations (food, being in the oral cavity, causes salivation). Conditioned reflex - a reaction to the properties (signs) of a stimulus (the smell of food, the type of food causes salivation). Conditioned reactions are always signaling in nature. They signal the upcoming action of the stimulus, and the body meets the influence of the unconditioned stimulus when all the responses that ensure the body is balanced by the factors that cause this unconditioned reflex are already included. So, for example, food, entering the oral cavity, encounters saliva there, released conditionally reflexively (at the sight of food, at its smell); muscular work begins when the conditioned reflexes developed for it have already caused a redistribution of blood, increased breathing and blood circulation, etc. This reveals the highest adaptive nature of conditioned reflexes.

7. Conditioned reflexes are developed on the basis of unconditioned ones.

8. A conditioned reflex is a complex multicomponent reaction.

9. Conditioned reflexes can be developed in real life and in laboratory conditions.

A conditioned reflex is a multicomponent adaptive reaction of a signal nature, carried out by the higher parts of the central nervous system through the formation of temporary connections between the signal stimulus and the signaled reaction.

In the zone of the cortical representation of the conditioned stimulus and the cortical (or subcortical) representation of the unconditioned stimulus, two foci of excitation are formed. The focus of excitation caused by an unconditional stimulus of the external or internal environment of the body, as a stronger (dominant) one, attracts to itself excitation from the focus of weaker excitation caused by the conditioned stimulus. After several repeated presentations of the conditioned and unconditioned stimuli, a stable path of excitation movement is “trodden” between these two zones: from the focus caused by the conditioned stimulus to the focus caused by the unconditioned stimulus. As a result, the isolated presentation of only the conditioned stimulus now leads to the response caused by the previously unconditioned stimulus.

The main cellular elements of the central mechanism for the formation of a conditioned reflex are intercalary and associative neurons of the cerebral cortex.

For the formation of a conditioned reflex it is necessary to comply following rules: 1) an indifferent stimulus (which must become conditioned, signal) must have sufficient strength to excite certain receptors; 2) it is necessary that the indifferent stimulus be reinforced by an unconditioned stimulus, and the indifferent stimulus must either slightly precede or be presented simultaneously with the unconditioned one; 3) it is necessary that the stimulus used as a conditional stimulus be weaker than the unconditional one. To develop a conditioned reflex, normal physiological state cortical and subcortical structures that form the central representation of the corresponding conditioned and unconditioned stimuli, the absence of strong extraneous stimuli, the absence of significant pathological processes in the body.

Parasympathetic nervous system consists of two sections: the brain (medulla oblongata and midbrain) and the sacral, and its ganglia are located either near the innervated organ or directly in it.

The parasympathetic nervous system also regulates the activity of almost all tissues and organs.

The mediator that transmits excitation of the parasympathetic nervous system is acetylcholine.

Excitation of parasympathetic centers is observed in a state of rest - during sleep, rest, after eating. In this case, the following vegetative reactions occur:

· bronchi dilate, breathing slows down;

· heart contractions slow down and weaken;

· blood pressure in the vessels decreases;

· skin vessels dilate;

· blood vessels of organs dilate abdominal cavity and digestion processes are enhanced;

· the processes of urine formation intensify;

· the work of the endocrine glands and sweat glands slows down;

· the pupil of the eye narrows;

· skeletal muscles relax;

· inhibition of brain neurons occurs - drowsiness occurs;

· the amount of blood in the vessels decreases, a certain amount of it leaves the vessels to the liver and spleen.

Neurons of the sympathetic and parasympathetic system take part in the formation of certain autonomic reflexes. Autonomic reflexes manifest themselves in changes in the state of internal organs when the body position changes and when receptors are irritated.

Autonomic reflexes are of the following types:

· viscero-visceral reflexes;

· cutanovisceral reflexes;

· motor-visceral reflexes;

· eye-heart reflex.

Viscero-visceral reflexes – These are those reactions that are caused by irritation of the receptors of internal organs and are manifested by a change in the condition of the internal organs. For example, when narrowing blood vessels the amount of blood in the spleen increases.

Cutanovisceral reflexes– are expressed in the fact that when certain areas of the skin are irritated, vascular reactions and changes in the activity of certain internal organs occur. For example, acupressure skin affects the condition of internal organs. Or, applying cold to the skin causes blood vessels to constrict.

Motor-visceral reflexes- manifest themselves in changes in value blood pressure and the number of heart contractions when changing body position. For example, if a person moves from a lying position to a sitting position, then his blood pressure will increase and the heart will contract more strongly.

Oculocardiac reflex- manifests itself in changes in heart function when the eyeball is irritated.

- Autonomic reflexes and centers for the regulation of autonomic functions

Pharmacological ways of modulating the work of vegetative synapses I. Excitation of cholinergic and adrenoreactive apparatuses can occur through indirect action For example, inactivation of cholinesterase: physostigmine and proserine. In this case, acetylcholine is not destroyed, and...

Viscero-visceral reflexes are caused by irritation of interoreceptors (visceroreceptors) located in the internal organs. They play an important role in the functional interaction of internal organs and their self-regulation. These reflexes include viscerocardial, cardiocardiac, gastrohepatic, etc. Some patients with damage to the stomach experience gastrocardial syndrome, one of the manifestations of which is disruption of the heart, up to the appearance of angina attacks caused by insufficient coronary circulation.

Viscerodermal reflexes occur when the receptors of the visceral organs are irritated and are manifested by impaired skin sensitivity, sweating, and skin elasticity in limited areas of the skin surface (dermatome). Such reflexes can be observed in the clinic. Thus, with diseases of the internal organs, tactile (hyperesthesia) and pain (hyperalgesia) sensitivity increases in limited areas of the skin. It is possible that painful and non-painful cutaneous afferent fibers and visceral afferents belonging to a specific segment of the spinal cord are converted on the same neurons of the sympothalamic pathway.

Visceromotor and motor-visceral reflexes. The manifestation of the segmental organization of the autonomic innervation of internal organs is also associated with visceromotor reflexes, in which excitation of the receptors of internal organs leads to a reduction or inhibition of the current activity of skeletal muscles.

The activity of the body is a natural reflex reaction to a stimulus. Reflex is the body’s reaction 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.

A reflex arc is a sequentially connected chain of nerve cells that ensures the implementation of a reaction, a response to stimulation.

The reflex arc consists of six components: receptors, afferent pathway, reflex center, efferent 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 consist of 3 neurons (there may be more) - a receptor, one or more intercalary and an effector.

The feedback loop establishes a connection between the realized result of the reflex response 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) reflex arc two-neuron, monosynaptic;

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

4) short time reflex;

5) muscles contracting according to the type of single muscle contraction.

Features of a complex monosynaptic reflex arc:

1) territorially separated receptor and effector;

2) three-neuron receptor arch;

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

4) muscle contraction according to the tetanus type. Features of the autonomic reflex:

1) the interneuron is located in the lateral horns;

2) the preganglionic begins from the lateral horns neural pathway, after the ganglion - postganglionic;

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

The difference between the sympathetic nervous arch and the parasympathetic: the sympathetic nervous arch has a short preganglionic pathway, since the autonomic ganglion lies closer to the spinal cord, and the postganglionic pathway is long.

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

The mechanism of reflex action (by modern ideas): 1 - spinal cord (transverse plane); 2 - muscle; 3 - skin; 4 - skin receptor; 5 - muscle receptor (muscle spindle); 6, 7 - afferent conductors; 8 - afferent neurons (cells): 9 - motor neuron (motor cell); 10 - intermediate neurons (interneurons); 11 - motor conductor; 12 - neuromuscular synapse.

Neurons of the autonomic nervous system are involved in many reflex reactions, called autonomic reflexes. The latter can be caused by irritation of both intero- and exteroceptors. The criterion for classifying a reflex as a vegetative one is the receipt of impulses to the efferent peripheral organ with the central nervous system sympathetic or parasympathetic nerves.

Reflexes of the ganglia of the autonomic nervous system. Reflexes of the metasympathetic department

Many autonomic ganglia perform the function of being located in the periphery reflex centers. They have all the structures necessary to perform reflex switching. The intramural ganglia and nerve plexuses present in empty organs are no exception. These ganglia are part of the efferent pathway of the parasympathetic nervous system. But at the same time, nerve cells come to them from internal organ receptors, there are also interneurons here, therefore, already in the ganglion itself, the transfer of influences from the receptor neuron to the efferent one is possible. Weighty arguments In favor of the presence of receptor neurons in the peripheral nerve ganglia, facts of preservation of afferent, intercalary and efferent neurons and nerve fibers coming from them, as well as local internal organ reflex regulation in the transplanted heart, were revealed. If these receptors, nerve cells and nerve fibers belonged to neurons whose bodies are located in the central nervous system, that is, outside the transplanted heart, their degeneration should occur.

The structure of the intramural ganglia resembles typical nerve centers. Each neuron is surrounded by a large number neuroglia cells. In addition, there are structures that selectively allow only certain substances from the blood to reach the neuron, which in their function resemble the BBB. Thus, ganglion neurons, like brain neurons, are protected from the direct effects of substances circulating in the blood

Among the structures of the metasympathetic division of the autonomic nervous system is pacemaker cells, that have the ability to spontaneous depolarization, which ensures the rhythm of activity and the reduction of all disturbances muscle cells organ. This activity is corrected by impulses of its own afferentation depending on the state of the organ and its individual parts.

“Local” peripheral reflexes, which are performed by the intramural autonomic ganglia, regulate the functioning of the heart, intestinal motility, and interconnect various parts of the stomach and some other organs. The neurons entering these ganglia, their processes, synapses and endings form intraorgan reflex structures that regulate the functioning of the organ with internal peripheral reflexes.

The influence of parasympathetic nerve centers on metasympathetic reflexes.

Impulses entering the organ by preganglionic fibers of the parasympathetic nerves interact with impulses that carry out the processes of internal organ reflex regulation. The nature of the organ's response determines the result of this interaction. Therefore, the effect of irritation of preganglionic fibers is not unambiguous. On organs in which intramural reflex mechanisms of regulation are found, preganglionic parasympathetic fibers can have (depending on the functional state of the organ that is innervated) both exciting, so and inhibitory influence.

The opposite influences of parasympathetic fibers are by no means “paradoxical”. This is a natural manifestation of multidirectional influences necessary to ensure the normal function of organs and tissues. The parasympathetic department is a system capable of carrying out ongoing regulation physiological processes and ensure full maintenance of the constancy of the internal environment of the body. The number of intramural neurons per 1 cm2 of intestinal surface can reach 20,000. As a consequence, only one part of the metasympathetic system, which is located in the intestines, contains approximately the same number of neurons as the entire spinal cord.

Thus, impulses arriving to the organ by preganglionic fibers of the parasympathetic nerves interact with impulses that carry out the processes of internal organ reflex regulation. Depending on the current state of physiological processes in this organ or system, they can turn on or off, strengthen or weaken this or that function of the organ, carrying out a variety of regulatory influences necessary to maintain normal current activities and homeostasis.

Physiological significance of "local" reflexes.

Efferent intramural neurons are the common final pathway for impulses of intraorgan and extraorgan (central) origin. The presence of “local” mechanisms of nervous regulation of the functions of internal organs, which is carried out with the help of peripheral reflexes by the ganglia of the autonomic nervous system, internal and external organs, is of great physiological importance. As a result this The central nervous system is freed from the need to process excess information coming from internal organs. In addition, peripheral reflexes increase the reliability of regulation of the physiological functions of these organs. Such regulation, being basic, aimed at maintaining homeostasis. At the same time, if necessary, it can be easily corrected by higher levels of the autonomic nervous system and humoral mechanisms. In addition, this regulation can also occur after the connection between organs and the central nervous system is turned off.

Spinal reflexes

At the level of the spinal cord, the reflex arcs of many autonomic reflexes close (Fig. 58).

The nature of the reflex response is largely determined by the presence of nerve centers of the sympathetic (thoracolumbar) and parasympathetic (sacral) divisions of the autonomic nervous system. The spinal section of the sympathetic nervous system has signs of a segmental (metameric) organization. This is expressed in the fact that a clear switching of sensory inputs to efferent ones occurs within a specific segment. Although there are also zones of overlap of adjacent segments, in this case the response to irritation of adjacent roots is less pronounced. The most indicative in this regard are the reflexes of the cardiovascular system and excretory organs (cardio-cardiac, gastrointestinal, evacuation reflexes).

The interneuronal apparatus of the spinal cord ensures the interaction of reflex pathways both within the autonomic nervous system and between it and the somatic nervous system. As a result, the wide involvement of various internal organs in the reflex response is ensured. It is also important that the reflex can be started from the receptors of one, and end with the effectors of another part of the nervous system.

Spinal centers for the regulation of autonomic functions.

At the level of the last cervical and two upper thoracic segments of the spinal cord there are neurons that innervate the three muscles of the eye: the muscle that dilates the pupil, the orbital part of the orbicularis oculi muscle and one of the muscles of the upper eyelid.

In the upper thoracic segments of the spinal cord there are neurons that are part of the center, which regulates the functioning of the heart and the condition of the blood vessels (see section 3). There are neurons that innervate the bronchi.

In all thoracic and upper lumbar segments of the spinal cord there are neurons that innervate the sweat glands. Defeats of individual segments

Rice. 58.(along the legs): afferent pathways of each nerve of the somatic nervous system (1). autonomic nerve (2), somatic reflex (3), autonomic reflex (4)

cops causes the cessation of sweating in areas of the body that have lost sympathetic innervation.

The sacral portion of the spinal cord contains the spinal centers for the reflexes of urination, defecation, erection and ejaculation. The destruction of these centers causes impotence, urinary and fecal incontinence. Disorders of urination and defecation occur due to paralysis of the closing muscles of the bladder and rectum.

Autonomic reflexes can be divided into: Viscero-visceral, viscerodermal And dermatovisceral.

Viscero-visceral reflexes are caused by irritation of receptors located in internal organs and end with a change in the activity of internal organs. In addition, these reflexes can begin and end in the organs of one functional system(for example, cardiovascular) or be intersystemic. Viscero-visceral reflexes include reflex changes in cardiac activity, vascular tone, blood supply to the spleen due to an increase or decrease in pressure in the aorta, carotid sinus or pulmonary vessels, reflex cardiac arrest due to irritation of the abdominal organs, etc.

Viscerodermal reflexes occur when internal organs are irritated and manifest themselves in changes in sweating, electrical resistance (electrical conductivity) of the skin and skin sensitivity in limited areas of the body surface, the topography of which varies depending on which organ is irritated.

Dermatovisceral reflexes are expressed in the fact that when certain areas of the skin are irritated, vascular reactions occur and changes in the activity of certain internal organs.

Many of these autonomic reflexes are used in practical medicine, and their application is multifaceted.

An example of the use of the dermatovisceral reflex in the clinic is the use of heating pads or, conversely, ice packs to influence the pathological focus in the internal organs. Therapeutic effect different types of acupuncture are also based on similar reflexes. Viscerodermal reflexes are often used in the diagnosis of pathology of internal organs. Thus, the development of a pathological focus in any internal organ can increase the sensitivity of certain areas of the skin, which is manifested by their pain with a light touch or even without an irritant (referred pain in the Ged-Zakharyin zones) (Fig. 59). Such a reflex can begin with interoceptors, and skeletal muscles can become an effector: during a “fire” in the abdominal cavity, the

Rice. 59. 1-section of the lungs and bronchi; 2 -heart area; WITH- part of the intestines; 4,5 - area of the bladder; b- kidney area; 7,9 - area of the liver; 8 - area of the stomach and pancreas; 10 - area of the urinary and genital organs

The tone of the flexor muscles is felt (the person curls up into a ball), the muscles of certain parts of the abdominal wall tense.

Spinal shock.

These reflexes of the spinal cord in the whole organism are coordinated by the higher parts of the central nervous system. This clearly manifests itself after the connection between the brain and spinal cord is broken. As a result of such damage, as in the somatic nervous system, there appears spinal shock- temporary disappearance of autonomic reflexes of the spinal cord. Reflexes disappeared gradually, over 1-6 months. are restored, even such complex ones as emptying the bladder, colon, and genitals.

Restoration of spinal reflexes after spinal shock may be associated with the activation of former or the formation of new synapses on intercalary preganglionic and motor neurons.

In this situation, the parasympathetic (vagal) reflex arcs are not damaged.

Brain stem reflexes

The autonomic centers of the brain stem are involved in the regulation of the functions of the cardiovascular and digestive systems, which carry out evacuation reflexes, control the reproductive organs, controlling their innervation by autonomic nerves. Here the spinal centers responsible for individual autonomic functions are united into functional complexes.

The medulla oblongata contains the boulevard section of the vasomotor center, which regulates the function of the heart and the condition of the blood vessels. It also contains centers that stimulate lacrimation and secretion of the salivary and gastric glands, pancreas, cause the release of bile from the gallbladder and bile duct, and stimulate the motility of the stomach and small intestine.

In the middle of the brain (in the anterior tubercles of the chotirigubic plate) there are nerve centers for the pupillary reflex and accommodation of the eye. In the anterior part of the midbrain is located one of the centers that are involved in emptying the bladder. These centers refer to parasympathetic division. But in the whole organism, in order to perform the reflex function, many of them (this is especially clearly demonstrated in the example of the vasomotor center) closely interact with other parts of the central nervous system. Thus, the vasomotor center of the medulla oblongata functions together with the sympathetic section of the thoracic region, and evacuation reflexes are carried out through the interaction of the centers of the brainstem with the Krijo centers of the parasympathetic nervous system. (These reflexes are discussed in more detail when presenting the relevant sections.)

Reflex regulation of functions by the nerve centers of the trunk is carried out with the direct participation of interneuron mechanisms that are responsible for the intercentral interaction of various parts of the central nervous system: sympathetic, parasympathetic, autonomic and somatic nervous systems. A good example- respiratory-cardiac reflex, or so-called respiratory arrhythmia: slowing of heart contractions at the end of exhalation before the next inhalation begins.

Naturally, all brain stem reflexes are under the control of the higher parts of the central nervous system. For example, the above evacuation reflexes are controlled by the cerebral cortex.

IN medical practice autonomic reflexes of the brain stem are used. For example, some reflexes that close here make it possible to determine the state of the autonomic nervous system (autonomic functional tests). These include: a) osocervical reflex, or Danin-Aschner reflex (short-term slowing of heartbeat when pressing on eyeballs); b) orthostatic reaction(increased heart rate and increased blood pressure during a change from a lying position to a standing position), etc.

Reflex

1). by origin:

conditional (acquired);

spinal (spinal cord);

· food;

· defensive;

· sexual

· indicative;

What are somatic and autonomic reflexes? How are their reflex arcs different?

Somatic reflex - the general name of reflexes manifested by changes in the tone of skeletal muscles or their contraction under any influence on the body. For somatic reflexes, the effector organ is the skeletal muscles, that is, as a result of a reflex act, certain muscles or muscle groups contract and some kind of movement occurs.

Autonomic reflexes are caused by irritation of both intero- and exteroceptors. Among the numerous and varied autonomic reflexes, viscero-visceral, viscerodermal, dermatovisceral, visceromotor and motor-visceral are distinguished.

The autonomic and somatic reflex arcs are built according to the same plan and consist of sensitive, associative and efferent circuits. They may share sensory neurons. The differences are that in the arc of the autonomic reflex, the efferent autonomic cells lie in ganglia outside the central nervous system.

What is a reflex arc and a reflex ring?

The material basis of the reflex is the “reflex arc”. According to I. P. Pavlov’s definition, “ reflex arc “is the anatomical substrate of the reflex,” or in other words, the path of passage of the excitation impulse from the receptor through the central nervous system to the working organ. The simplest reflex arc necessarily includes 5 components:

1). receptor;

2). afferent (centripetal) nerve;

3). nerve center;

4). efferent (centrifugal) nerve;

5). effector organ (working organ).

In the doctrine of reflex there is a concept - “ reflex ring " According to this concept, from receptors executive body(effector), the excitation impulse is sent again to the central nervous system, despite the fact that the reflex has already been carried out. This is necessary to evaluate and adjust the response performed.

What are extero-, intero- and proprioceptors?

Exteroceptors (receptors outer surface body);

interoreceptors or visceral (receptors of internal organs and tissues);

· proprioceptors (receptors of skeletal muscles, tendons, ligaments);

Nerve centers and their properties

In complex multicellular organisms of humans and animals, a single nerve cell is not able to regulate any functions. All main forms of activity of the central nervous system are provided by groups of nerve cells called the “nerve center”. Nerve center is a collection of brain neurons necessary to perform a specific function.

All nerve centers are united by common properties. These properties are largely determined by the work of synapses between neurons in nerve centers. The main properties of nerve centers include: unilateral conductivity, delay in excitation, summation, irradiation, transformation, aftereffect, inertia, tone, fatigue, plasticity.

One way conduction

In the nerve centers of the brain, excitation spreads only in one direction - from the afferent to the efferent neuron. This is due to the unilateral conduction of excitation through the synapse.

Excitation delay

The speed of excitation through the nerve centers slows down significantly. The reason lies in the peculiarities of synaptic transmission of excitation from one neuron to another. In this case, the following processes occur at the synapse, requiring a certain amount of time:

1). release of a mediator by the nerve ending of a synapse in response to an excitation impulse arriving at it;

2). diffusion of the transmitter through the synaptic cleft;

3). the appearance of an excitatory postsynaptic potential under the influence of a mediator.

This decrease in the speed of excitation in the nerve centers was called central delay. The more synapses on the excitation path, the greater the delay. It takes 1.5-2 milliseconds to conduct excitation through one synapse.

Excitation summation

This property of nerve centers was discovered in 1863 by I.M. Sechenov. There are two types of summation of excitation in nerve centers: temporary (sequential) and spatial.

Temporal summation is understood as the emergence or strengthening of a reflex under the action of weak and frequent stimuli, each of which individually, respectively, either does not cause a response or the response to it is very weak. So, if a single subthreshold irritation is applied to a frog’s paw, the animal is calm, but if a whole series of such frequent irritations is applied, the frog withdraws its paw.

Spatial summation is observed in the case of simultaneous arrival of nerve impulses in the same neuron along different afferent pathways, i.e. with simultaneous stimulation of several receptors of the same “receptive field”. The receptive field (reflexogenic zone) is a part of the body, when the receptors of which are irritated, a certain reflex act occurs.

The mechanism of summation is that in response to a single afferent wave (weak stimulus) going from receptors to neurons of the brain, or upon stimulation of one receptor of a specific receptive field, not enough transmitter is released in the presynaptic part of the synapse for an excitatory postsynaptic potential to occur on the postsynaptic membrane (EPSP). In order for the EPSP value to reach a “critical level” (10 millivolts) and an action potential to arise, the summation of many subthreshold EPSPs on the cell membrane is required.

Irradiation of excitation

Under the influence of strong and prolonged irritations, general excitation of the central nervous system is observed. Such excitation, spreading in a “broad wave,” was called irradiation. Irradiation is possible due to the huge number of collaterals (additional bypass paths) existing between individual neurons of the brain.

Aftereffect

After the end of the stimulus, the active state of the nerve cell (nerve center) remains for some time. This phenomenon was called aftereffect. The aftereffect mechanism is based on a long-term trace depolarization of the neuron membrane, which usually occurs as a result of prolonged rhythmic stimulation. On the wave of depolarization, a series of new action potentials may arise, “supporting” the reflex act without irritation. But in this case, only a short-term aftereffect is observed. The longer-lasting effect is explained by the possibility of long-term circulation of nerve impulses along closed circular pathways of neurons within the same nerve center. Sometimes such “stray” waves of excitation can enter the main path and thus “support” the reflex act, despite the fact that the effect of the main stimulus has long ended.

Short aftereffects (lasting about an hour) are the basis of the so-called. short-term (working) memory.

Inertia

In the nerve centers, traces of previous excitations may remain longer for a long time than what happens during the aftereffect. Thus, in the brain they do not disappear for several days, but in the cerebral cortex they remain for decades. This property of nerve centers is called inertia. Even I.P. Pavlov believed that this property underlies memory mechanisms. Modern physiological science adheres to a similar point of view. According to the biochemical theory of memory (Hiden), in the process of memorization there are structural changes in ribonucleic acid (RNA) molecules contained in nerve cells that conduct certain excitation waves. This leads to the synthesis of “changed” proteins that form the biochemical basis of memory. Unlike the aftereffect, inertia provides the so-called. long-term memory.

Fatigue

Fatigue of the nerve centers is characterized by a weakening or complete cessation of the reflex reaction with prolonged stimulation of the afferent pathways of the reflex arc. The cause of fatigue of the nerve centers is a violation of the transmission of excitation in interneuron synapses. This is caused by a sharp decrease in the reserves of the transmitter in the axon endings and a decrease in the sensitivity of the receptors of the postsynaptic membrane to it.

Tone

The tone of the nerve centers is the state of their slight constant excitation in which they remain. Tone is maintained by a continuous, rare flow of afferent impulses from numerous peripheral receptors, which leads to the release of a small amount of transmitter into the synaptic cleft.

Plastic

Plasticity is the ability of nerve centers to change or rearrange their function if necessary.

Coordination of nervous processes

The central nervous system constantly receives many excitation impulses coming from numerous extero-, intero- and proprioceptors. The central nervous system responds to these stimuli strictly selectively. This is ensured by one of the most important functions of the brain - coordination of reflex processes.

Coordination of reflex processes – this is the interaction of neurons, synapses, nerve centers and the processes of excitation and inhibition occurring in them, thanks to which the coordinated activity of various organs, vital systems and the body as a whole is ensured.

Coordination of nervous processes is possible due to the following phenomena:

Dominant

Dominant - this is a temporary, persistent excitation that dominates in any nerve center of the brain, subjugating all other centers and thereby determining the specific and appropriate nature of the body’s response not to external and internal stimuli. The principle of dominance was formulated by the Russian scientist A. A. Ukhtomsky.

The dominant focus of excitation is characterized by the following basic properties: increased excitability, the ability to summarize excitations, persistence of excitation, and inertia. The dominant center in the central nervous system is able to attract (attract) nerve impulses from other nerve centers that are less excited at the moment. Due to these impulses, which are not addressed to him, his excitement is even more intensified, and the activity of other centers is suppressed.

Dominants can be of exogenous and endogenous origin.

Exogenous dominance occurs under the influence of environmental factors. For example, a dog during training can be distracted from work by the appearance of some stronger stimulus: a cat, a loud shot, an explosion, etc.

The endogenous dominant is created by factors of the internal environment of the body. These can be hormones, physiologically active substances, metabolic products, etc. Thus, when the content of nutrients (especially glucose) in the blood decreases, the food center is excited and a feeling of hunger appears. From this moment on, the behavior of a person or animal will be focused exclusively on searching for food and satiation.

The most persistent dominants in humans and animals are food, sexual and defensive.

Feedback

Important for normal operation The principle of coordination in the brain is feedback (reverse afferentation). Every reflex act does not end immediately after the “command” received in the form of a flow of impulses from the brain to the effector organ. So, despite the fact that the working organ has carried out this “command”, reverse waves of excitation (secondary afferentation) are sent from its receptors to the central nervous system, signaling the degree and quality of the organ’s implementation of the “task” of the center. This allows the center to “compare” the actual result with what was planned and, if necessary, correct the reflex act. Thus, secondary afferent impulses carry out a function that in technology is called feedback.

Convergence

One of the conditions for the normal coordination of reflex processes is the principle of convergence and the principle of a common final path, discovered by the English physiologist Charles Sherrington. The essence of this discovery is that impulses arriving in the central nervous system along different afferent pathways can converge on the same intermediate and efferent neurons. This is facilitated, as noted earlier, by the fact that the number of afferent neurons is 4-5 times greater than efferent ones. Associated with convergence, for example, is the mechanism of spatial summation of excitation in nerve centers.

To explain the above phenomenon, C. Sherrington proposed an illustration in the form of a “funnel,” which went down in history as the “Sherrington funnel.” Through its wide part, impulses enter the brain, through its narrow part, they exit.

General final path

The principle of a common final path should be understood as follows. A reflex act can be caused by irritation of a large number of different receptors, i.e. the same efferent neuron can be part of many reflex arcs. For example, turning the head, as the final reflex act, ends with irritation of various receptors (visual, auditory, tactile, etc.).

In 1896, N. E. Vvedensky, and somewhat later - Ch. Sherrington, discovered reciprocal (conjugate) innervation as a principle of coordination. An example is the work of antagonistic nerve centers. According to this principle, the excitation of one center is accompanied by reciprocal (conjugate) inhibition of the other. The basis of reciprocal innervation is translational postsynaptic inhibition.

Reciprocal inhibition

It underlies the functioning of antagonist muscles and ensures muscle relaxation at the moment of contraction of the antagonist muscle. The afferent fiber, which conducts excitation from muscle proprioceptors (for example, flexors), in the spinal cord is divided into two branches: one of them forms a synapse on the motor neuron innervating the flexor muscle, and the other - on the intercalary, inhibitory, forming an inhibitory synapse on the motor neuron innervating extensor muscle. As a result, excitation coming along the afferent fiber causes excitation of the motor neuron innervating the flexor muscle and inhibition of the motor neuron of the extensor muscle.

Induction

The name of the next principle of coordination of reflex processes - induction - was borrowed by physiologists from physicists (induction - “guidance”). There are two types of induction: simultaneous and sequential. By simultaneous induction we mean the induction by one process (excitation or inhibition), taking place in some nerve center, of a process of the opposite sign - in another center. Simultaneous induction is based on reciprocal inhibition in antagonist centers.

Sequential induction refers to contrasting changes in the state of the same nerve center after the cessation of excitatory or inhibitory stimulation. Such induction can be positive or negative. The first is accompanied by an increase in excitation in the center after the cessation of inhibition, the second, on the contrary, by an increase in inhibition after the cessation of excitation.

Spinal cord

The spinal cord is the most ancient part of the central nervous system of vertebrates. He is in spinal canal, covered meninges and surrounded on all sides cerebrospinal fluid(liquor).

In a cross section of the spinal cord, white and gray matter are distinguished. Gray matter, shaped like a butterfly, is represented by the bodies of nerve cells and has the so-called. “horns” - dorsal and ventral. White matter formed by processes of neurons. Two pairs of roots depart from each segment of the spinal cord - dorsal and ventral (in humans - posterior and anterior, respectively), which, when connected, form the peripheral spinal nerves. The dorsal roots are “responsible” for sensitivity, and the ventral roots are responsible for motor acts.

The spinal cord performs two important functions: reflex and conduction.

Reflex activity The spinal cord is determined by the presence in it of certain nerve centers responsible for specific reflex acts.

The most important centers This part of the brain is locomotor. They control and coordinate the work of the body's skeletal muscles, ensure the maintenance of their tone and are responsible for organizing elementary motor acts.

Special motor neurons located in the spinal cord innervate the respiratory muscles (in the area of 3-5 cervical vertebrae - the diaphragm, in the thoracic region - intercostal muscles).

The centers of defecation and genitourinary reflexes are localized in the sacral part of the spinal cord. Some parasympathetic and all sympathetic fibers depart from the spinal cord.

Conductor function The spinal cord is responsible for conducting impulses. This is provided by the white matter of the brain. The pathways of this part of the central nervous system are divided into ascending and descending. The first ones conduct excitations entering the central nervous system from numerous receptors to the brain, the second ones, on the contrary, from the brain to the spinal cord and effector organs.

The ascending tracts (tracts) of the spinal cord include: the Gaulle and Burdach bundles, the lateral and ventral spinothalamic tracts, the dorsal and ventral spinocerebellar tracts (Flexig and Gowers bundles, respectively).

The descending tracts of the spinal cord include: corticospinal (pyramidal) tract, rubrospinal (extrapyramidal) Monakov tract, vestibulospinal tracts, reticulospinal tract.

Hypothalamus and its functions

The hypothalamus (subthalamus) is the oldest formation of the brain, located under the visual thalamus. It is formed by 32 pairs of nuclei, the most important of which are: supraoptic, paraventricular, gray tubercle and mastoid body. The hypothalamus is connected to all parts of the central nervous system and is an intermediate link between the cerebral cortex and the autonomic nervous system. The hypothalamus contains nerve centers involved in the regulation of various metabolisms (protein, carbohydrate, fat, water-salt) and a thermoregulation center.

The hypothalamus forms a close morpho-functional connection with the pituitary gland - the “king” of all endocrine glands. The resulting so-called The “hypothalamic-pituitary system” combines the nervous and humoral mechanisms for regulating functions in the body. The hypothalamus is associated with many emotional and behavioral reactions.

The concept of reflexes. Classification of reflexes

Functional activity The central nervous system is, at its core, a reflex activity. It is based on a “reflex”.

Reflex - This is the body’s response to irritation with the participation of the central nervous system.

Reflexes are very diverse. They can be classified according to a number of characteristics into several groups:

1). by origin:

· unconditional (congenital, inherited);

conditional (acquired);

2). depending on the location of the receptors:

Exteroceptive (receptors on the external surface of the body);

· interoreceptive or visceral (receptors of internal organs and tissues);

· proprioceptive (receptors of skeletal muscles, tendons, ligaments);

3). according to the location in the central nervous system of the nerve centers “involved” in the implementation of the reflex: