Types of autonomic reflexes. Higher centers of autonomic regulation

Question.

The metsympathetic nervous system is a collection of microganglia located in organ tissue. They consist of three types of nerve cells - afferent, efferent and intercalary, therefore, they perform the following functions:

1) provides intraorganic innervation;

2) are an intermediate link between the tissue and the extraorganic nervous system. Under the action of a weak stimulus, the metsympathetic department is activated, and everything is decided at the local level. When strong impulses are received, they are transmitted through the parasympathetic and sympathetic divisions to the central ganglia, where they are processed.

The metsympathetic nervous system regulates the work of smooth muscles that are part of most organs of the gastrointestinal tract, myocardium, secretory activity, local immunological reactions, etc.

2question.

Sympathetic nervous system carries out the innervation of all organs and tissues (stimulates the work of the heart, increases the lumen of the respiratory tract, inhibits the secretory, motor and absorption activity of the gastrointestinal tract, etc.). It performs homeostatic and adaptive-trophic functions.

Its homeostatic role is to maintain the constancy of the internal environment of the body in an active state, i.e., the sympathetic nervous system is included in the work only during physical exertion, emotional reactions, stress, pain effects, blood loss.

The adaptive-trophic function is aimed at regulating the intensity of metabolic processes. This ensures the adaptation of the organism to the changing conditions of the environment of existence.

Thus, the sympathetic department begins to act in an active state and ensures the functioning of organs and tissues.

parasympathetic nervous system is a sympathetic antagonist and performs homeostatic and protective functions, regulates the emptying of hollow organs.

The homeostatic role is restorative and operates at rest. This manifests itself in the form of a decrease in the frequency and strength of heart contractions, stimulation of the activity of the gastrointestinal tract with a decrease in blood glucose levels, etc.

All protective reflexes rid the body of foreign particles. For example, coughing clears the throat, sneezing clears the nasal passages, vomiting causes food to be expelled, etc.

Emptying of hollow organs occurs with an increase in the tone of smooth muscles that make up the wall. This leads to the entry of nerve impulses into the central nervous system, where they are processed and sent along the effector path to the sphincters, causing them to relax.

Relationships between sympathetic and parasympathetic regulation of functions. Since most of the effects of sympathetic and parasympathetic nervous regulation are opposite, their relationship is sometimes characterized as antagonistic. The existing interrelationships between higher autonomic centers and even at the level of postganglionic synapses in tissues receiving double innervation makes it possible to apply the concept of reciprocal regulation.

However, the interaction of the parasympathetic and sympathetic nervous systems can be not only antagonistic, but also synergistic. So, for example, both departments cause an increase in salivation. Synergism is most clearly manifested in the effect on tissue trophism. In general, an increase in the tone of one section of the autonomic nervous system usually causes an increase in the activity of another section. The interaction of the two departments is also manifested in the implementation of adaptive reactions, when the sympathetic nervous system provides a quick "emergency" mobilization of energy resources and activates functional responses to stimuli, while the parasympathetic nervous system corrects and maintains homeostasis, providing reserves for active regulation. Therefore, it is believed that sympathetic influences provide ergotropic regulation of adaptation, and parasympathetic - trophotropic regulation.

3question.

Types of autonomic reflexes

Vegetative reflexes are usually divided into:
1) viscero-visceral, when both afferent and efferent links, i.e. the beginning and effect of the reflex refers to the internal organs or the internal environment (gastro-duodenal, gastrocardial, angiocardial, etc.);

2) viscero-somatic, when the reflex, which begins with irritation of the interoceptors, is realized in the form of a somatic effect due to the associative connections of the nerve centers. For example, when the chemoreceptors of the carotid sinus are irritated by an excess of carbon dioxide, the activity of the respiratory intercostal muscles increases and breathing becomes more frequent;

3) viscero-sensory, - change in sensory information from exteroceptors when stimulating interoceptors. For example, during oxygen starvation of the myocardium, there are so-called reflected pains in areas of the skin (Ged's zones) that receive sensory conductors from the same segments of the spinal cord;

4) somato-visceral, when, with stimulation of the afferent inputs of the somatic reflex, the vegetative reflex is realized. For example, during thermal irritation of the skin, the skin vessels expand and the vessels of the abdominal organs narrow.

Somatovegetative reflexes also include the Danini-Ashner reflex - a decrease in the pulse with pressure on the eyeballs.

Vegetative reflexes are also divided into segmental, those. implemented by the spinal cord and brain stem structures, and suprasegmental, the implementation of which is provided by the higher centers of autonomic regulation located in the suprasegmental structures of the brain.

axon-reflex occurs when skin receptors are irritated within the axon of one nerve cell, causing an expansion of the lumen of the vessel in this area .

Details

Fine sympathetic and parasympathetic systems are constantly active, and their basal levels of activity are known as sympathetic tone and parasympathetic tone, respectively.
The meaning of tone is that it allows the single nervous system to both increase and decrease the activity of the stimulated organ. For example, sympathetic tone normally keeps almost all systemic arterioles constricted to about half their maximum diameter. With an increase in the degree of sympathetic stimulation above the norm, these vessels can narrow even more; conversely, when stimulation decreases below normal, arterioles may dilate. In the absence of a constant background tone, sympathetic stimulation would only lead to vasoconstriction and never to their expansion.

Another interesting example of tone is the background parasympathetic tone in the gastrointestinal tract. Surgical removal of the parasympathetic supply to most of the intestine by cutting the vagus nerves can cause severe and prolonged atony of the stomach and intestines. As a result, a significant part of the normal movement of the contents forward is blocked, with the subsequent development of severe constipation. This example demonstrates the importance of having a normal parasympathetic tone in the digestive tract for its function. The tone can decrease, which inhibits the motility of the gastrointestinal tract, or increase, contributing to an increase in the activity of the digestive tract.

Tone associated with basal secretion of adrenaline and norepinephrine by the adrenal medulla. At rest, the adrenal medulla normally secretes approximately 0.2 μg/kg/min of epinephrine and approximately 0.05 μg/kg/min of norepinephrine. These amounts are significant as they are sufficient to maintain an almost normal blood pressure level even if all direct sympathetic pathways to the cardiovascular system are removed. Consequently, much of the overall tone of the sympathetic nervous system is the result of basal secretion of epinephrine or norepinephrine in addition to the tone resulting from direct sympathetic stimulation.

Reflexes of the autonomic nervous system.

Many visceral functions of the body are regulated by autonomic reflexes.

Cardiovascular autonomic reflexes.

Certain reflexes in the cardiovascular system help regulate blood pressure and heart rate. One of them is the baroreceptor reflex. In the walls of some large arteries, including the internal carotid arteries and the aortic arch, there are stretch receptors called baroreceptors. When stretched under high pressure, signals are transmitted to the brainstem, where they inhibit sympathetic impulses to the heart and blood vessels and excite the parasympathetic pathway; this allows blood pressure to return to normal.

Gastrointestinal autonomic reflexes.

The uppermost part of the digestive tract and the rectum are mainly regulated by vegetative reflexes. For example, the smell of tasty food or its ingestion in the mouth initiates signals sent from the nose and mouth to the nuclei of the vagus and glossopharyngeal nerves, as well as to the salivary nuclei of the brainstem. These, in turn, carry signals through the parasympathetic nerves to the secretory glands of the mouth and stomach, causing the secretion of digestive juices, sometimes even before the food enters the mouth.

When faecal matter fills the rectum at the other end of the alimentary canal, sensory impulses initiated by its distention are sent to the sacral spinal cord, and the reflex signal is conducted back through the sacral parasympathetic fibers to the distal colon; this leads to strong peristaltic contractions causing defecation.
Other autonomic reflexes. Bladder emptying is regulated in the same way as rectal emptying. Distension of the bladder causes impulses to travel to the sacral spinal cord, and this, in turn, causes a reflex contraction of the bladder and relaxation of the urinary tract sphincters, thus facilitating urination.

Sexual reflexes.

Also important are sexual reflexes, which are initiated by both mental stimuli from the brain and stimuli from the genital organs. Impulses from these sources converge at the level of the sacral spinal cord, which in men leads first to an erection, which is mainly a parasympathetic function, and then to ejaculation, which is partly a function of the sympathetic system.

Other functions of autonomic control include the regulation of pancreatic secretion, gallbladder emptying, urinary excretion by the kidney, sweating, and blood glucose concentration.

The role of adrenaline and norepinephrine in the autonomic nervous system.

Sympathetic stimulation of the adrenal medulla causes the release of large amounts of adrenaline and norepinephrine into the circulating blood, and these two hormones are in turn carried by the blood to all body tissues. On average, about 80% of the secret is epinephrine, and 20% is norepinephrine, although the relative proportion can vary markedly under different physiological conditions.

Circulating epinephrine and norepinephrine have almost the same effect on various organs that occurs with direct sympathetic stimulation, except that the effects last 5-10 times longer, since both substances are removed from the blood slowly - within 2-4 minutes.

Circulating norepinephrine causes constriction of almost all blood vessels in the body; it also enhances the activity of the heart, inhibits the activity of the gastrointestinal tract, dilates the pupils of the eyes, etc.
Epinephrine produces the same effects as norepinephrine, but there are some differences. First of all, adrenaline due to more pronounced stimulation of beta receptors has a stronger effect on the heart than norepinephrine. Second, epinephrine causes only a slight constriction of the blood vessels in the muscles compared to the much stronger constriction caused by norepinephrine. Since muscle vessels make up the majority of the body's vessels, this distinction is especially important because norepinephrine significantly increases total peripheral resistance and increases blood pressure, while epinephrine raises pressure to a lesser extent, but increases cardiac output more.

Third difference between the action of adrenaline and noradrenaline is associated with their effect on tissue metabolism. Adrenaline has a 5-10 times longer metabolic effect than norepinephrine. Indeed, adrenaline, secreted by the adrenal medulla, can increase the metabolic rate of the whole body by more than 100% above normal, thus increasing the activity and excitability of the body. It also increases the rate of other metabolic events, such as glycogenolysis in the liver and muscles and the release of glucose into the blood.

Autonomic reflexes are an integral part of the autonomic nervous system responsible for the functioning of internal organs - respiration, digestion, the hematopoietic system, etc., their regulation and operational state.

Reflex arc - basic concepts

Reflex - a typical, standard response of the human body to irritation (irritation or stimulation), embodied with the help of the nervous system.

The main basic component of the reflex is the reflex arc (vegetative reflex arc), which is a complex of morphologically interconnected formations responsible for the perception, transmission and processing of signals required to implement the body's reaction.

Pathways - chains or links consisting of neurons that are conductors of signals from perception receptors and, conversely, to the nervous system. They differ in direction, that is, in the strict direction of movement of signals from and to the center of the nervous system - afferent, associative and efferent paths.

The arc structure includes the following elements:

• Receptors are sensors that perceive irritation of the environment and internal environment of a person.
• Afferent conductors that provide signal transmission to the nerve center.
• Efferent conductor responsible for the transmission of signals from the nerve center to the effector.
• The effector is the executive organs of the system.

Types of vegetative reflexes and their significance in the organization of the body's work

Vegetative reflexes by their nature and types of relationships between the channels for receiving and transmitting nerve signals should be divided into:

1. Viscero-visceral, when the elements of the reflex arc are in the internal environment of the body or its organs. These types of reactions are very important for the functioning of internal organs and their self-regulation.
2. Viscerodermal arise when stimulating signals are received by the nerve endings of the internal organs and are expressed by changes in the sensitivity of the skin. Such types of reactions are observed in medical institutions, when, with certain diseases of the organs, a violation of tactile and pain sensitivity is observed in certain areas of the skin, such as an echo of pain in the left hand with angina pectoris.
3. Dermatovisceral reflexes are expressed in the fact that when certain areas of the skin are stimulated, changes occur in the work of human organs. Many methods of medical and preventive procedures widely used in medical practice are based on this principle of operation of the system.
4. Visceromotor reflexes. So, when the nerve endings of the internal organs are stimulated, inhibition or high activity of the skeletal muscle mass occurs.
5. Motor-visceral reflexes are the opposite, that is, with the active activity of the muscles, stimulation of the organs occurs, which is used in physiotherapy exercises and treatment.

Often, such reactions occur in acute organ disease, for example, with appendicitis, muscle tension occurs in the abdomen, which in essence is a protective measure for the abdominal cavity. Also, such reflexes realize forced protective postures in certain diseases.

How do higher regulatory centers influence the vegetative system?

In addition to the reactions presented above, in the brain and spinal cord there are a significant number of complexes of formations that change or affect the work of the entire vegetative system of the body, depending on its needs.

There are three levels of regulation:

First level. At this level, the maintenance of autonomous work of the entire autonomic nervous system of the body is ensured; these reactions are not associated with strong environmental factors. Despite the fact that a significant part of these functions is concentrated in parts of the spinal cord such as the centers of respiration, swallowing, etc., the majority is concentrated in the hypothalamus, which is responsible for most of the visceral functions. So, for example, stimulation of the nuclei of the hypothalamus leads to an increase in blood pressure, an increase in sugar, and leads to aggressive human behavior.

The second level is aimed at coordinating the vegetative system in the interaction of the body with the environment, through the vegetative support of the organs. This level is associated with a truly huge number of processes in the spinal cord, limbic system and cerebellum. Thus, the spinal cord, which receives signals from the middle ear, regulates the tone of the skeletal muscle mass, the frequency of respiration, blood circulation, etc.

The third level is the implementation of optional vegetative support associated with human activity - mental, physical labor and behavior. Thus, the incoming signals to the brain make it possible to develop conditioned reactions, which, in turn, change the functioning of the organs. Independently, not every person can realize this, but almost everyone is able to do this under the influence of hypnosis. After special training and practice, a person can dramatically slow down the heartbeat, which is very often observed in yogis. The cerebral cortex is the highest level of the hierarchy, which is able to subjugate the other two levels.

Autonomic reflexes are the most important part of the nervous system, responsible for the autonomous operation of internal organs, as well as their interaction with the environment and human activities.

The regulation of the activity of internal organs is carried out by the nervous system through its special department - the autonomic nervous system.

Features of the structure of the autonomic nervous system. All functions of the body can be divided into somatic, or animal, associated with the activity of skeletal muscles - the organization of posture and movement in space, and vegetative, associated with the activity of internal organs - the processes of respiration, blood circulation, digestion, excretion, metabolism, growth and breeding. This division is conditional, since vegetative processes are also inherent in the motor apparatus (for example, metabolism, etc.); motor activity is inextricably linked with a change in respiration, blood circulation, etc.

Irritations of various body receptors and reflex responses of nerve centers can cause changes in both somatic and autonomic functions, i.e., the afferent and central sections of these reflex arcs are common. Only their efferent departments are different.

The totality of efferent nerve cells of the spinal cord and brain, as well as cells of special nodes (ganglia) that innervate the internal organs, is called the autonomic nervous system. Therefore, this system is the efferent part of the nervous system, through which the central nervous system controls the activity of internal organs.

A characteristic feature of the efferent pathways included in the reflex arcs of vegetative reflexes is their two-neuron structure. From the body of the first efferent neuron, which is located in the central nervous system (in the spinal, medulla oblongata or midbrain), a long axon departs, forming a prenodal (or preganglionic) fiber. In the autonomic ganglia - clusters of cell bodies outside the central nervous system - excitation switches to the second efferent neuron, from which the post-nodal (or postganglionic) fiber departs to the innervated organ.

The autonomic nervous system is divided into 2 divisions - sympathetic and parasympathetic. The efferent pathways of the sympathetic nervous system originate in the thoracic and lumbar regions of the spinal cord from the neurons of its lateral horns. The transfer of excitation from the pre-nodal sympathetic fibers to the post-nodal occurs in the ganglia of the border sympathetic trunks with the participation of the mediator acetylcholine, and the transfer of excitation from the post-nodal fibers to the innervated organs occurs with the participation of the mediator norepinephrine, or sympathin. The efferent pathways of the parasympathetic nervous system begin in the brain from some nuclei of the middle and medulla oblongata and from the neurons of the sacral spinal cord. Parasympathetic ganglia are located in the immediate vicinity of the innervated organs or inside them. Conduction of excitation in the synapses of the parasympathetic pathway occurs with the participation of the mediator acetylcholine.

The role of the autonomic nervous system in the body. The autonomic nervous system, regulating the activity of internal organs, increasing the metabolism of skeletal muscles, improving their blood supply, increasing the functional state of the nerve centers, etc., contributes to the implementation of the functions of the somatic and nervous system, which provides an active adaptive activity of the body in the external environment (reception of external signals, their processing, motor activity aimed at protecting the body, searching for food, in humans - motor acts associated with household, labor, sports activities, etc.). The transmission of nerve influences in the somatic nervous system is carried out at a high speed (thick somatic fibers have high excitability and a conduction speed of 50-140 m / s). Somatic effects on individual parts of the motor apparatus are characterized by high selectivity. The autonomic nervous system is involved in these adaptive reactions of the body, especially during extreme stress (stress).

Another significant aspect of the activity of the autonomic nervous system is its huge role in maintaining the constancy of the internal environment of the body.

The constancy of physiological parameters can be ensured in various ways. For example, the constancy of the level of blood pressure is maintained by changes in the activity of the heart, the lumen of blood vessels, the amount of circulating blood, its redistribution in the body, etc. In homeostatic reactions, along with nervous influences transmitted through autonomic fibers, humoral influences are important. All these influences, in contrast to somatic influences, are transmitted in the body much more slowly and more diffusely. Thin autonomic nerve fibers are characterized by low excitability and low speed of conduction of excitation (in prenodal fibers, the speed of conduction is 3–20 m/s, and in postnodal fibers, 0.5–3 m/s).

All nervous influences are divided into starting, including the activity of the body, and trophic, changing its metabolism and functional state. Many influences of the autonomic nervous system can be considered as trophic.

Functions of the sympathetic division of the autonomic nervous system. With the participation of this department, many important reflexes in the body occur, aimed at ensuring its active state, including motor activity. These include reflexes of bronchial expansion, increased and increased heart rate, vasodilation of the heart and lungs with simultaneous narrowing of the vessels of the skin and abdominal organs (providing redistribution of blood), the release of deposited blood from the liver and spleen, the breakdown of glycogen to glucose in the liver (mobilization of carbohydrate sources of energy), increased activity of the endocrine glands of the sweat glands. The sympathetic department of the nervous system reduces the activity of a number of internal organs: as a result of vasoconstriction in the kidneys, the processes of urination decrease, the secretory and motor activity of the organs of the gastrointestinal tract is inhibited, the act of urination is prevented (the muscle of the bladder wall relaxes and its sphincter is reduced). Increased activity of the body is accompanied by a sympathetic pupil dilation reflex.

Of great importance for the motor activity of the body is the trophic influence of sympathetic nerves on skeletal muscles. Stimulation of these nerves does not cause muscle contraction. However, the reduced amplitude of contractions of a tired muscle can increase again when the sympathetic nervous system is excited - the Orbeli - Ginetsinsky effect. Strengthening of contractions can also be observed on an untired muscle, attaching irritations of sympathetic fibers to irritations of the motor nerves. Moreover, sympathetic influences on the skeletal muscles in the whole organism arise earlier than the triggering influences of the motor nerves, preparing the muscles for work in advance. The most important importance of sympathetic influences for the adaptation (adaptation) of the body to work, to various environmental conditions, which is reflected in his teaching on the adaptive-trophic role of the sympathetic nervous system.

Functions of the parasympathetic division of the autonomic nervous system. This department of the nervous system takes an active part in the regulation of the activity of internal organs, in the processes of restoring the body after an active state.

The parasympathetic nervous system constricts the bronchi, slows down and weakens the heartbeat; narrowing of the vessels of the heart; replenishment of energy resources (glycogen synthesis in the liver and strengthening of digestion processes); strengthening the processes of urination in the kidneys and ensuring the act of urination (contraction of the muscles of the bladder and relaxation of its sphincter), etc.

The parasympathetic nervous system, in contrast to the sympathetic one, mainly exerts triggering influences: constriction of the pupil, activation of the activity of the digestive glands, etc.

Autonomic reflexes are classified by:

1. According to the level of closing the reflex arc to:

Ø central (spinal, hypothalamic, cortical);

Ø peripheral (intra- and extramural, as well as axon reflexes).

2. According to the location of the receptor and the effector organ:

1. Viscero-visceral reflexes include the ways in which excitation arises and ends in the internal organs. With such reflexes, the internal organ can respond in two ways: either by inhibition or by strengthening functions. For example, with mechanical irritation of the mesentery, the heart rate slows down (Goltz reflex); irritation of the carotid or aortic reflexogenic zone causes a change in the intensity of respiration, the level of blood pressure, heart rate.

A variation of the viscero-visceral reflex is axon reflex. It occurs when a nerve fiber (axon) branches and, due to this, innervates one organ with one branch, and another organ or another part of the organ with the other branch. As a result of irritation, excitation from one branch can spread to another branch, resulting in changes in the activity of several organs. The axon reflex explains the mechanism of the occurrence of a vascular reaction (constriction or expansion of blood vessels) upon irritation of skin, pain receptors.

2. Viscerodermal reflexes. They occur when internal organs are irritated and are manifested in a change in sweating, changes in the tone of skin vessels, an increase in tactile and pain sensitivity of certain areas of the skin. For example, pain in the heart radiates to the left arm. These pains are named reflected, and the areas of their manifestation - zones Zakharyin-Ged. This is due to the fact that irritation from the internal organs for a long time enters a certain segment of the spinal cord and leads to a change in the properties of neurons in this segment. Sensory nerves from the skin and muscles approach these segments, so the sensitivity of the skin in the region of innervation by this segment changes.

3. Viscerosomatic reflexes. They occur when internal organs are irritated and, in addition to visceral ones, cause a somatic reaction. For example, inhibition of general motor activity during irritation of the sensitive endings of the carotid sinus zone, as well as contraction of the muscles of the abdominal wall or twitching of the limbs during irritation of the receptors of the digestive tract.

4. Viscerosensory reflex carried out along the same pathways as viscerosomatic, however, for its occurrence, a longer and stronger effect is needed. The reaction occurs not only in the internal organs, the somatic muscular system, but in addition to this, the somatic sensitivity changes. The area of ​​increased perception is usually limited to the area of ​​the skin innervated by the segment to which impulses from the irritated visceral organ are received.