The autonomic nervous system

The autonomic nervous system (systema nervosum autonomicum) is a part of the nervous system that controls the functions of internal organs, glands, vessels, carries out an adaptive-trophic influence on all human organs. The vegetative nervous system maintains the constancy of the internal environment of the organism (homeostasis). The function of the autonomic nervous system is beyond the control of human consciousness, but it is in the subordination of the spinal cord, cerebellum, hypothalamus, basal nuclei of the terminal brain, limbic system, reticular formation and cerebral cortex.

Isolation of the autonomic nervous system is due to certain features of its structure. These features include the following:

1. foci of the location of vegetative nuclei in the central nervous system;
2. accumulation of bodies of effector neurons in the form of nodes (ganglia) in the composition of peripheral vegetative plexuses;
3. the two-neuronality of the nervous path from the nuclei in the CNS to the innervated organ;
4. preservation of signs reflecting the slower evolution of the autonomic nervous system (in comparison with the animal): a smaller caliber of nerve fibers, a lower rate of excitation, and the absence of myelin sheath in many nerve wires.

The autonomic nervous system is divided into the central and peripheral parts.

The central department includes:

1. parasympathetic nuclei of III, VII, IX and X pairs of cranial nerves lying in the brain stem (middle brain, bridge, medulla oblongata);
2. parasympathetic sacral nuclei occurring in the gray matter of the three sacral segments of the spinal cord (SII-SIV);
3. vegetative (sympathetic) nucleus located in the lateral intermediate column [lateral intermediate (gray) substance] VIII cervical, all thoracic and two upper lumbar segments of the spinal cord (СVIII-ТhI-LII).

The peripheral part of the autonomic (autonomic) nervous system includes:

1. autonomic (autonomic) nerves, branches and nerve fibers emerging from the brain and spinal cord;
2. autonomic visceral plexus;
3. nodes of vegetative (autonomous, visceral) plexuses;
4. sympathetic trunk (right and left) with its nodes, interstitial and connecting branches and sympathetic nerves;
5. nodes of the parasympathetic part of the autonomic nervous system;
6. vegetative fibers (parasympathetic and sympathetic), going to the periphery (to organs, tissues) from vegetative nodes that are part of the plexus and located in the thickness of internal organs;
7. nerve endings involved in vegetative reactions.

Neurons of the nuclei of the central part of the autonomic nervous system are the first efferent neurons on the pathways from the central nervous system (spinal cord and brain) to the innervated organ. The fibers formed by the processes of these neurons are called preganglionic nerve fibers, since they go to the nodes of the peripheral part of the autonomic nervous system and end with synapses on the cells of these nodes.

Vegetative nodes are part of the sympathetic trunks, large vegetative plexuses of the abdominal cavity and pelvis, and are located in the thickness or near the organs of the digestive, respiratory and urogenital apparatus, which are innervated by the autonomic nervous system.

Dimensions of vegetative nodes are due to the number of cells located in them, which ranges from 3000-5000 to many thousands. Each node is enclosed in a connective tissue capsule, the fibers of which, penetrating into the depth of the node, divide it into segments (sectors). Between the capsule and the body of the neuron are satellite cells - a kind of glial cells.

Glial cells (Schwann cells) include neurolematocytes, which form the shells of peripheral nerves. Neurons of vegetative ganglia are divided into two main types: Dogel cells of type I and type II. Dogel cells of type I are efferent, they terminate preganglionic processes. For these cells, a long thin nonbranching axon and a set (from 5 to several tens) of dendrites, branching near the body of this neuron, are typical. These cells have several slightly branched processes, among which there is an axon. They are larger than Dogel type I neurons. Their axons enter into a synaptic connection with the efferent neurons of Dogel type I.

Preganglionic fibers have a myelin sheath, so they differ in whitish color. They leave the brain as part of the roots of the corresponding cranial and spinal nerves. The nodes of the peripheral part of the autonomic nervous system contain the bodies of the second efferent (effector) neurons lying on the way to the innervated organs. The processes of these second neurons, which carry a nerve impulse from the vegetative nodes to the working organs (smooth muscles, glands, vessels, tissues), are post-nodular (postganglionic) nerve fibers. They do not have a myelin sheath, and therefore they have a gray color.

The speed of impulses along sympathetic preganglionic fibers is 1.5-4 m / s, and parasympathetic fibers - 10-20 m / s. The rate of impulse conduction on postganglionic (demihelin) fibers does not exceed 1 m / s.

The bodies of the afferent nerve fibers of the autonomic nervous system are located in the spinal (intervertebral) nodes, as well as in the sensitive nodes of the cranial nerves; in their own sensitive nodes of the autonomic nervous system (Dogel type II cells).

The structure of the reflex autonomic arc differs from the structure of the reflex arc of the somatic part of the nervous system. In the reflex arc of the autonomic nervous system, the efferent link consists not of a single neuron, but of two. In general, a simple vegetative reflex arc is represented by three neurons. The first link of the reflex arc is a sensitive neuron whose body is located in the spinal nodes or nodes of the cranial nerves. The peripheral process of such a neuron, which has a sensitive end-the receptor, originates in organs and tissues. The central process in the posterior roots of the spinal nerves or the sensitive roots of the cranial nerves is directed to the corresponding vegetative nuclei of the spinal cord or brain. The efferent (enduring) path of the autonomic reflex arc is represented by two neurons. The body of the first of these neurons, the second one in a simple vegetative reflex arc, is located in the autonomic nuclei of the central nervous system. This neuron can be called intercalary, because it is located between the sensitive (afferent, bringing) link of the reflex arc and the third (efferent, enduring) neuron of the efferent pathway. The effector neuron is the third neuron of the autonomic reflex arc. The bodies of effector neurons lie in peripheral nodes of the autonomic nervous system (sympathetic trunk, vegetative nodes of the cranial nerves, nodes of extra- and intraorganic vegetative plexuses). The processes of these neurons are directed to organs and tissues in the composition of organ vegetative or mixed nerves. Postganglionic nerve fibers terminate in smooth muscles, glands, in the walls of the vessels and in other tissues with the corresponding terminal nerves.

Based on the topography of vegetative nuclei and nodes, differences in the length of the first and second neurons of the efferent path, as well as features of functions, the autonomic nervous system is divided into two parts: sympathetic and parasympathetic.

Physiology of the autonomic nervous system

The autonomic nervous system controls blood pressure (BP), heart rate (heart rate), temperature and body weight, digestion, metabolism, water-electrolyte balance, sweating, urination, defecation, sexual reactions and other processes. Many organs are governed mainly by either sympathetic or parasympathetic system, although they can receive incoming impulses from both parts of the autonomic nervous system. More often the action of the sympathetic and parasympathetic systems on the same organ is directly opposite, for example sympathetic stimulation increases the heart rate, and parasympathetic stimulation reduces.

The sympathetic nervous system promotes intensive activity of the organism (catabolic processes) and hormonally provides a phase of response to stress "fight or run." So, sympathetic efferent signals increase the heart rate and contractility of the myocardium, cause bronchodilation, activate glycogenolysis in the liver and release glucose, increase the speed of basal metabolism and muscle strength; and also stimulate sweating on the palms. Less vital in the stressful situation, life-supporting functions (digestion, renal filtration) are reduced under the influence of the sympathetic autonomic nervous system. But the process of ejaculation is completely under the control of the sympathetic department of the autonomic nervous system.

The parasympathetic nervous system helps restore the resources expended by the body, i.e. Provides anabolic processes. The parasympathetic autonomic nervous system stimulates the secretion of the digestive glands and the motility of the gastrointestinal tract (including evacuation), reduces the heart rate and blood pressure, and also provides an erection.

The functions of the autonomic nervous system are provided by two main neurotransmitters, acetylcholine and norepinephrine. Depending on the chemical nature of the mediator, nerve fibers secreting acetylcholine are called cholinergic; These are all preganglionic and all postganglionic parasympathetic fibers. Fibers that secrete norepinephrine are called adrenergic; they are the majority of postganglionic sympathetic fibers, with the exception of innervating blood vessels, sweat glands and muscles arectores pilorum, which are cholinergic. The palmar and plantar sweat glands partially respond to adrenergic stimulation. The subtypes of adrenergic and cholinergic receptors are distinguished depending on their location.

Evaluation of the autonomic nervous system

It is possible to suspect vegetative dysfunction in the presence of such symptoms as orthostatic hypotension, lack of tolerance to high temperature and loss of control over the function of the intestine and bladder. Erectile dysfunction is one of the early symptoms of dysfunction of the autonomic nervous system. Xerophthalmia and xerostomia are not specific symptoms of dysfunction of the autonomic nervous system.

[1], [2], [3], [4], [5], [6], [7], [8]

Physical examination

Steady decrease in systolic blood pressure by more than 20 mm Hg. Art. Or diastolic by more than 10 mm Hg. Art. After taking a vertical position (in the absence of dehydration of the body) suggests the presence of autonomic dysfunction. One should pay attention to changes in heart rate (HR) during breathing and when the body position changes. Absence of respiratory arrhythmia and insufficient increase in heart rate after taking a vertical position indicate vegetative dysfunction.

Mioz and moderate ptosis (Horner's syndrome) testify to the defeat of the sympathetic part of the autonomic nervous system, the dilated pupil (the pupil of Adi), which is not reacting to light, is about the defeat of the parasympathetic autonomic nervous system.

Pathological genitourinary and rectal reflexes can also be symptoms of a deficiency in the autonomic nervous system. The study includes evaluation of the cremaster reflex (normally a dashed skin irritation of the thigh leads to a rise in the testicles), an anal reflex (normally the dashed stimulation of the perianal skin leads to a reduction in the anal sphincter) and bulbocavernous reflex (normal compression of the glans penis or clitoris leads to a reduction in the anal sphincter ).

Laboratory research

In the presence of symptoms of autonomic dysfunction in order to determine the degree of severity of the pathological process and objective quantitative evaluation of the vegetative regulation of the cardiovascular system, a cardiovascular test, samples for the sensitivity of peripheral a-drenoreceptors, and a quantitative assessment of sweating are performed.

The quantitative navigational axonreflectstem checks the function of postganglionic neurons. Local sweating is stimulated by iontophoresis of acetylcholine, electrodes are placed on the tibia and wrist, the intensity of sweating is recorded by a special meter that transmits information to the computer in analog form. The result of the test can be a decrease in sweating, or lack of it, or the persistence of sweating after the termination of stimulation. With the help of a thermoregulatory sample, the state of preganglionic and postganglionic conducting paths is evaluated. Significantly less frequently, coloring tests are used to evaluate sweating. After application to the skin, the patient's dyes are placed in a closed room, which is heated until the maximum sweating is achieved; sweating leads to a discoloration of the paint, which reveals the areas of anhidrosis and hypohydrosis and allows for their quantitative analysis. Absence of sweating indicates the defeat of the efferent part of the reflex arc.

Cardiovascular tests assess the response of the heart rate (ECG recording and analysis) to deep breathing and the Valsalva test. If the autonomic nervous system is intact, the maximum increase in heart rate is observed after the 15th heart beat and the decrease after the 30th. The ratio between the RR intervals at the 15th to 30th strokes (ie, the longest interval to the shortest one) - the ratio of 30:15 - is normally 1.4 (the Valsalva ratio).

The sensitivity tests for peripheral adrenergic receptors include the study of heart rate and blood pressure in a tilt test (passive orthotropic test) and a Valsalva test. When carrying out a passive orthotropic test, the blood volume is redistributed into the lower body parts, which causes reflex hemodynamic reactions. In the Valsalva test, the changes in blood pressure and heart rate are evaluated as a result of an increase in chest pressure (and a decrease in venous influx), which causes characteristic changes in blood pressure and reflex vasoconstriction. Normally, changes in hemodynamic parameters take place during 1.5-2 minutes and have 4 phases, during which the blood pressure rises (the 1 st and 4 th phases) or decreases after rapid recovery (phases 2 and 3). The heart rate increases in the first 10 s. When the sympathetic department is affected, blockade of the response occurs in the 2 nd phase.