Autonomic nervous system: structure, function, pathology

The autonomic nervous system (ANS, ganglionic, visceral, organ, autonomic) is a complex mechanism that regulates the internal environment in the body.

The division of the brain into functional elements is described rather conditionally, since it is a complex, well-oiled mechanism. The ANS, on the one hand, coordinates the activity of its structures, and on the other hand, it is exposed to the influence of the cortex.

General information about VNS

The visceral system is responsible for many tasks. The higher nerve centers are responsible for the coordination of the ANS.

The neuron is the main structural unit of the ANS. The path along which impulse signals travel is called a reflex arc. Neurons are required to conduct impulses from the spinal cord and brain to somatic organs, glands, and smooth muscle tissue. An interesting fact is that the heart muscle is represented by striated tissue, but it also contracts involuntarily. Thus, autonomic neurons regulate the heart rate, the secretion of the endocrine and exocrine glands, intestinal peristaltic contractions, and many other functions.

ANS is subdivided into sympathetic and parasympathetic subsystems (SNS and PNS, respectively). They differ in the specificity of innervation and the nature of the reaction to substances that affect the ANS, but at the same time they closely interact with each other - both functionally and anatomically. Sympathetic is stimulated by adrenaline, parasympathetic - by acetylcholine. The former is inhibited by ergotamine, the latter by atropine.

Functions of the ANS in the human body

The tasks of the autonomous system include the regulation of all internal processes occurring in the body: the work of the somatic organs, blood vessels, glands, muscles, sense organs.

ANS maintains the stability of the internal environment of a person and the implementation of such vital functions as breathing, blood circulation, digestion, temperature regulation, metabolic processes, excretion, reproduction and others.

The ganglionic system is involved in the adaptive and trophic processes, i.e. regulates metabolism according to external conditions.

Thus, the vegetative functions are as follows:

• support for homeostasis (immutability of the environment);
• adaptation of organs to various exogenous conditions (for example, in the cold, heat transfer decreases, and heat production increases);
• vegetative realization of mental and physical activity of a person.

ANS structure (how it works)

Consideration of the structure of the ANS by levels:

Suprasegmental

It includes the hypothalamus, the reticular formation (wakefulness and falling asleep), the visceral brain (behavioral reactions and emotions).

The hypothalamus is a small layer of medulla. It has thirty-two pairs of nuclei that are responsible for neuroendocrine regulation and homeostasis. The hypothalamic site interacts with the cerebrospinal fluid circulation system, since it is located next to the third ventricle and subarachnoid space.

In this area of ​​the brain, there is no gliosis layer between neurons and capillaries, which is why the hypothalamus immediately responds to a change in the chemical composition of the blood.

The hypothalamus interacts with the organs of the endocrine system by sending oxytocin and vasopressin to the pituitary gland, as well as releasing factors. The visceral brain (psychoemotional background during hormonal changes) and the cerebral cortex are associated with the hypothalamus.

So, the work of this important area is dependent on the cortex and subcortical structures. The hypothalamus is the highest center of the ANS, which regulates various types of metabolism, immune processes, and maintains the stability of the environment.

Segmental

Its elements are localized in the spinal segments and basal nuclei. This includes SMN and PNS. Sympathetic includes the Yakubovich nucleus (regulation of the muscles of the eye, constriction of the pupil), nuclei of the ninth and tenth pairs cranial nerves (the act of swallowing, providing nerve impulses to the cardiovascular and respiratory systems, gastrointestinal tract).

The parasympathetic system includes the centers located in the sacral spinal region (innervation of the genital and urinary organs, rectal region). From the centers of this system, fibers emanate, reaching the target organs. This is how each specific body is regulated.

The centers of the cervicothoracic region form the sympathetic part. Short fibers emerge from the gray matter nuclei and branch out in organs.

Thus, sympathetic irritation manifests itself everywhere - in different parts of the body. Acetylcholine is involved in sympathetic regulation, and adrenaline is involved in the periphery. Both subsystems interact with the other, but not always antagonistically (the sweat glands are innervated only sympathetically).

Peripheral

It is represented by fibers entering the peripheral nerves and ending in organs and blood vessels. Particular attention is paid to the autonomic neuroregulation of the digestive system - an autonomous formation that regulates peristalsis, secretory function, etc.

Vegetative fibers, in contrast to the somatic system, are devoid of the myelin sheath. Because of this, the speed of transmission of pulses through them is 10 times less.

Sympathetic and parasympathetic

All organs are under the influence of these subsystems, except for the sweat glands, blood vessels and the inner layer of the adrenal glands, which are innervated only sympathetically.

The parasympathetic structure is considered to be more ancient. It contributes to the creation of stability in the work of organs and conditions for the formation of an energy reserve. The sympathetic division changes these states depending on the function performed.

Both departments interact closely. When certain conditions occur, one of them is activated, and the second is temporarily inhibited. If the tone of the parasympathetic department predominates, parasympathotonia occurs, the sympathetic - sympathotonia. For the former, a state of sleep is characteristic, for the latter, heightened emotional reactions (anger, fright, etc.).

Command Centers

Command centers are located in the cortex, hypothalamus, brain stem and lateral spinal horns.

Peripheral sympathetic fibers emanate from the lateral horns. The sympathetic trunk stretches along the spinal column and unites twenty-four pairs of sympathetic nodes:

• three neck;
• twelve chest;
• five lumbar;
• four sacral.

The cells of the cervical node form the nerve plexus of the carotid artery, the cells of the lower - the upper cardiac nerve. The thoracic nodes provide innervation to the aorta, broncho-pulmonary system, abdominal organs, lumbar - organs in the small pelvis.

In the midbrain, the mesencephalic section is located, in which the nuclei of the cranial nerves are concentrated: the third pair is the Yakubovich nucleus (mydriasis), the central posterior nucleus (innervation of the ciliated muscle). The medulla oblongata is also called the bulbar region, the nerve fibers of which are responsible for the processes of salivation. Also here is the vegetative nucleus, which innervates the heart, bronchi, gastrointestinal tract and other organs.

Nerve cells of the sacral level innervate the urogenital organs, the rectal gastrointestinal tract.

In addition to these structures, the fundamental system, the so-called "base" of the ANS, is distinguished - this is the hypothalamic-pituitary system, the cerebral cortex and the striatum. The hypothalamus is a kind of "conductor" that regulates all underlying structures, controls the work of the endocrine glands.

VNS Center

The leading regulatory link is the hypothalamus. Its nuclei communicate with the cerebral cortex and the underlying sections of the trunk.

The role of the hypothalamus:

• close relationship with all elements of the brain and spinal cord;
• implementation of neuroreflex and neurohumoral functions.

The hypothalamus is permeated by a large number of vessels through which protein molecules penetrate well. Thus, this is a rather vulnerable area - against the background of any diseases of the central nervous system, organic damage, the work of the hypothalamus is easily disrupted.

The hypothalamic region regulates falling asleep and awakening, many metabolic processes, hormonal levels, the work of the heart and other organs.

Formation and development of the central nervous system

The brain is formed from the front wide part of the brain tube. Its posterior end is transformed into the spinal cord as the fetus develops.

At the initial stage of formation with the help of constrictions, three cerebral vesicles arise:

• diamond-shaped - closer to the spinal cord;
• average;
• front.

Further, from the rhomboid region, the medulla oblongata and hindbrain are formed. The forebrain is subdivided into the terminal and intermediate. All the structural elements of the brain are formed from these bubbles.

The canal located inside the anterior part of the cerebral tube, as it develops, changes its shape, size and is modified in the cavity - the ventricles of the human brain.

Allocate:

• lateral ventricles - endbrain cavities;
• 3rd ventricle - represented by the cavity of the diencephalon;
• brain aqueduct - the cavity of the midbrain;
• 4th ventricle - the cavity of the posterior and medulla oblongata.

All ventricles are filled with cerebrospinal fluid.

VNS dysfunctions

When the ANS malfunctions, a variety of disorders are observed. Most of the pathological processes entail not the loss of a particular function, but increased nervous excitability.

Problems in some departments of the ANS can spread to others. The specificity and severity of symptoms depend on the affected level.

Damage to the cortex leads to the emergence of vegetative, psychoemotional disorders, tissue nutritional disorders.

The reasons are varied: trauma, infections, toxic effects. At the same time, patients are restless, aggressive, exhausted, they have increased sweating, fluctuations in the frequency of heart contractions and pressure.

When the limbic system is irritated, vegetative-visceral seizures (gastrointestinal tract, cardiovascular, etc.) appear. Psycho-vegetative and emotional disorders develop: depression, anxiety, etc.

In case of damage to the hypothalamic area (neoplasms, inflammation, toxic effects, injury, violation circulation) develop vegetative-trophic (sleep disorders, thermoregulatory function, stomach ulcers) and endocrine violations.

Damage to the nodes of the sympathetic trunk leads to impaired sweating, hyperemia of the cervico-facial region, hoarseness or loss of voice, etc.

Dysfunction of the peripheral parts of the ANS often causes sympathetic (painful sensations of various localization). Patients complain of a burning or pressing nature of the pain, often there is a tendency to spread.

Conditions may develop in which the functions of various organs are disrupted due to the activation of one part of the ANS and oppression of the other. Parasympatotonia is accompanied by asthma, urticaria, runny nose, sympathotonia - migraine, transient hypertension, panic attacks.