Sympathetic part of the autonomic nervous system

The central division of the sympathetic part of the autonomic nervous system consists of numerous multipolar cells, neurocytes multipolares located in the lateral intermediate (gray) matter spinal cord throughout from the 8th cervical to the 2nd–3rd lumbar segments (see Fig.,) and together forming the sympathetic center.

Peripheral department The sympathetic part of the autonomic [autonomic] nervous system consists of the right and left sympathetic trunks and nerves extending from these trunks, as well as plexuses formed by nerves and nodes that lie outside or inside the organs.

Each sympathetic trunk, truncus sympathicus (Fig.,; see Fig.,), is formed by nodes of the sympathetic trunk, ganglia trunci sympathici, which are interconnected by internodal branches, rr. interganglionares.

The right and left sympathetic trunks lie on their respective sides spinal column from the level of the base of the skull to the top of the coccyx, where, ending, they connect unpaired ganglion impar.

The nodes of the sympathetic trunk are a collection of varying numbers of nerve cells ( neurocytes gangliae autonomicae), have different sizes and are predominantly spindle-shaped. Along the sympathetic trunk there are single intrastem nerve cells or small intermediate nodes, ganglia intermedia, most often on the cervical and lumbar connecting branches. Number of nodes of the sympathetic trunk, excluding cervical spine, basically corresponds to the number of spinal nerves.

There are 3 cervical node, ganglia cervicalia, 10–12 thoracic nodes, ganglia thoracica, 4–5 lumbar nodes, ganglia lumbalia, 4 sacral node, ganglia sacralia, and one unpaired ganglion impar. The latter lies on the anterior surface of the coccyx, uniting both sympathetic trunks.

From each node of the sympathetic trunk there are two kinds of branches: connecting branches and branches that go to the vegetative (autonomous) plexuses (see Fig.,).

In turn, there are two types of connecting branches: white connecting branches and gray connecting branches.

Each white connecting branch, r. communications albus, is a collection preganglionares nerve fibers connecting the spinal cord with the sympathetic ganglion. It contains myelin nerve fibers (processes of nerve cells of the lateral horns of the spinal cord), which pass through the anterior root to the cells of the sympathetic trunk node or, after passing it, to the cells of the autonomic plexus node. These fibers, since they end on ganglion cells, are called prenodal nerve fibers.

The lateral horns are located only within the range from the 8th cervical to the 2nd–3rd lumbar segments of the spinal cord. Therefore, prenodal fibers for those nodes of the sympathetic trunks that are located above and below the level of the indicated segments, i.e., for the neck, lower lumbar and entire sacral region, follow in the internodal branches of the sympathetic trunk.

Each gray connecting branch, r. communications griseus, is a branch connecting the sympathetic trunk with the spinal nerve. It contains nonmyelinated nerve fibers, neurofibrae nonmyelinatae(processes of cells of the node of the sympathetic trunk), which are sent to spinal nerve and are part of its fibers, reaching the glands and blood vessels catfish.

These fibers, since they originate from ganglion cells, are called postganglionares nerve fibers.

The branches going to the autonomic plexuses are different at the nodes of the cervical, thoracic, lumbar and sacral sections of the sympathetic trunk.

The sympathetic system mobilizes the body’s forces in emergency situations, increases the waste of energy resources; parasympathetic - promotes restoration and accumulation of energy resources.

The activity of the sympathetic nervous system and the secretion of adrenaline by the adrenal medulla are related to each other, but do not always change to the same extent. Thus, with particularly strong stimulation of the sympathoadrenal system (for example, during general cooling or intense physical activity), the secretion of adrenaline increases, enhancing the action of the sympathetic nervous system. In other situations, sympathetic activity and adrenaline secretion may be independent. In particular, the orthostatic response primarily involves the sympathetic nervous system, while the response to hypoglycemia primarily involves the adrenal medulla.

Most preganglionic sympathetic neurons have thin myelinated axons - B fibers. However, some axons are unmyelinated C-fibers. The conduction velocity along these axons ranges from 1 to 20 m/s. They leave the spinal cord as part of the ventral roots and white communicating rami and end in paired paravertebral ganglia or unpaired prevertebral ganglia. Through nerve branches, the paraventebral ganglia are connected into sympathetic trunks running on both sides of the spine from the base of the skull to the sacrum. Thinner unmyelinated postganglionic axons arise from the sympathetic trunks, which either go to peripheral organs as part of the gray connecting branches, or form special nerves going to the organs of the head, chest, abdominal and pelvic cavities. Postganglionic fibers from the prevertebral ganglia (celiac, superior and inferior mesenteric) go through the plexuses or as part of special nerves to the organs abdominal cavity and organs of the pelvic cavity.

Preganglionic axons leave the spinal cord as part of the anterior root and enter the paravertebral ganglion at the level of the same segment through the white communicating branches. White connecting branches are present only at levels Th1-L2. Preganglionic axons end at synapses in this ganglion or, after passing through it, enter the sympathetic trunk (sympathetic chain) of the paravertebral ganglia or the splanchnic nerve (Fig. 41.2).

As part of the sympathetic chain, preganglionic axons are directed rostrally or caudally to the nearest or distant paravertebral ganglion and form synapses there. Having left it, the axons go to the spinal nerve, usually through the gray communicating branch, which is present in each of the 31 pairs of spinal nerves. Included peripheral nerves postganglionic axons enter the effectors of the skin (piloerection muscles, blood vessels, sweat glands), muscles, and joints. Typically, postganglionic axons are unmyelinated (C fibers), although there are exceptions. The differences between the white and gray connecting branches depend on their relative content of myelinated and unmyelinated axons.

As part of the splanchnic nerve, preganglionic axons often go to the prevertebral ganglion, where they form synapses, or they can pass through the ganglion, ending in a more distal ganglion. Some of them, running as part of the splanchnic nerve, end directly on the cells of the adrenal medulla.

The sympathetic chain stretches from the cervical to the coccygeal level of the spinal cord. It acts as a distribution system, allowing preganglionic neurons, which are located only in the thoracic and upper lumbar segments, to activate postganglionic neurons, which supply all segments of the body. However, there are fewer paravertebral ganglia than spinal segments, since some ganglia fuse during ontogeny. For example, the superior cervical sympathetic ganglion is composed of fused C1-C4 ganglia, the middle cervical sympathetic ganglion is composed of C5-C6, and the inferior cervical sympathetic ganglion is composed of C7-C8. The stellate ganglion is formed by the fusion of the inferior cervical sympathetic ganglion with the Th1 ganglion. The superior cervical ganglion provides postganglionic innervation to the head and neck, and the middle cervical and stellate - the heart, lungs and bronchi.

Typically, the axons of preganglionic sympathetic neurons distribute to the ipsilateral ganglia and therefore regulate autonomic functions on the same side of the body. An important exception is the bilateral sympathetic innervation of the intestines and pelvic organs. Like the motor nerves of skeletal muscles, the axons of preganglionic sympathetic neurons belonging to specific organs innervate several segments. Thus, preganglionic sympathetic neurons that provide sympathetic functions to the head and neck areas are located in the C8-Th5 segments, and those belonging to the adrenal glands are in Th4-Th12.

The sympathetic division of the autonomic nervous system is divided into central and peripheral parts. The central part of the sympathetic nervous system includes suprasegmental and segmental centers.

Suprasegmental centers are located in the cerebral cortex, basal ganglia, limbic system, hypothalamus, reticular formation, and cerebellum.

The central segmental centers are in the lateral intermediate nuclei of the lateral horns of the spinal cord, starting from C VIII to L II segments.

The peripheral part of the sympathetic nervous system includes autonomic nodes of the first and second order.

Nodes of the first order (paravertebral or paravertebral), there are 20-25 pairs of them, they form the sympathetic trunk.

Nodes of the second order (prevertebral) - celiac, superior mesenteric, aortorenal.

The sympathetic (Fig. 18) trunk is divided into: cervical, thoracic, lumbar, sacral, and coccygeal sections.

The cervical section of the sympathetic trunk is represented by 3 nodes: superior, middle and inferior, as well as their internodal branches.

The autonomic nerves that come from the sympathetic trunk are directed to the blood vessels, as well as to the organs of the head and neck.

The sympathetic nerves form plexuses around the carotid and vertebral arteries.

Along the course of the arteries of the same name, these plexuses are directed into the cranial cavity, where they give branches to the vessels, meninges and pituitary gland.

From the carotid plexus fibers go to the lacrimal, sweat, salivary glands, to the muscle that dilates the pupil, to the ear and submandibular nodes.

The organs of the neck receive sympathetic innervation through the laryngopharyngeal plexus from all three cervical nodes.

From each of the cervical nodes towards the chest cavity, the upper, middle and lower cardiac nerves depart, taking part in the formation of cardiac plexuses.

In the thoracic section of the sympathetic trunk there are up to 10-12 nodes. From 2 to 5 thoracic nodes, the thoracic cardiac branches depart, participating in the formation of the cardiac plexus.

Thin sympathetic nerves also extend from the thoracic nodes to the esophagus, lungs, and thoracic aorta, forming the esophageal, pulmonary, and thoracic aortic plexuses.

The greater splanchnic nerve departs from the fifth to ninth thoracic nodes, and the lesser splanchnic nerve departs from 10 and 11. Both nerves contain mainly preganglionic fibers that transit through the sympathetic ganglia. Through the diaphragm, these nerves penetrate the abdominal cavity and end on the neurons of the celiac (solar) plexus.

From the solar plexus postganglionic fibers go to the vessels, stomach, intestines and other abdominal organs.

The lumbar sympathetic trunk consists of 3-4 nodes. Branches extend from them to the largest visceral plexus, the solar one, as well as to the abdominal aortic plexus.

The sacral section of the sympathetic trunk is represented by 3-4 nodes, from which sympathetic nerves depart to the pelvic organs (Fig. 18).

Rice. 18. The structure of the sympathetic division of the autonomic nervous system (S.V. Savelyev, 2008)

Parasympathetic nervous system

In the parasympathetic nervous system there are three foci of fiber exit from the substance of the brain and spinal cord: mesencephalic, bulbar and sacral.

Parasympathetic fibers are usually components of spinal or cranial nerves.

Parasympathetic ganglia are located in close proximity to the innervated organs or in them themselves.

The parasympathetic division of the autonomic nervous system is divided into central and peripheral parts. The central part of the parasympathetic nervous system includes suprasegmental and segmental centers.

The central (cranial) section is represented by the nuclei of the III, VII, IX, X pairs of cranial nerves and the parasympathetic nuclei of the sacral segments of the spinal cord.

The peripheral section includes: preganglionic fibers in the cranial nerves and sacral spinal nerves (S 2 -S 4), cranial autonomic nodes, organ plexuses, postganglionic plexuses ending on the working organs.

In the parasympathetic nervous system, the following autonomic nodes are distinguished: ciliary, pterygopalatine, submandibular, sublingual, auricular (Fig. 19).

The ciliary node is located in the orbit. Its size is 1.5-2mm. Preganglionic fibers come to it from the Yakubovich nucleus (III pair), postganglionic fibers - as part of the ciliary nerves to the muscle that constricts the pupil.

Ear node, 3-4 mm in diameter, located in the area of ​​the outer base of the skull near the foramen ovale. Preganglionic fibers come to it from the inferior salivary nucleus and as part of the glossopharyngeal and then tympanic nerves. The latter penetrates the tympanic cavity, forming the tympanic plexus, from which the lesser petrosal nerve is formed, containing preganglionic fibers to the ear ganglion.

Postganglionic fibers (axons of parasympathetic neurons of the ear ganglion) go to the parotid gland as part of the auriculotemporal nerve.

Pterygopalatine node (4-5 mm ) located in the pit of the same name.

Preganglionic fibers go to the pterygopalatine ganglion from the superior salivary nucleus, located in the tegmentum of the bridge, as part of the facial nerve (intermediate). In the channel temporal bone The greater petrosal nerve arises from the facial nerve and connects with the deep petrosal nerve (sympathetic), forming the nerve of the pterygoid canal.

After leaving the pyramid of the temporal bone, this nerve penetrates the pterygopalatine fossa and comes into contact with the neurons of the pterygopalatine ganglion. Postganglionic fibers come from the pterygopalatine ganglion, join the maxillary nerve, innervating the mucous membrane of the nose, palate, and pharynx.

Some of the preganglionic parasympathetic fibers from the superior salivary nucleus, which are not included in the greater petrosal nerve, form the chorda tympani. The chorda tympani emerges from the pyramid of the temporal bone, joins the lingual nerve and, as part of it, goes to the submandibular and sublingual nodes, from which postganglionic fibers to the salivary glands begin.

Nervus vagus – the main collector of the parasympathetic nerve pathways. Preganglionic fibers from the dorsal nucleus of the vagus nerve travel along numerous branches of the vagus nerve to the organs of the neck, chest and abdominal cavities. They end on the neurons of the parasympathetic nodes, periorgan and intraorgan autonomic plexuses.

For parenchymal organs these nodes are periorgan or intraorgan, for hollow organs they are intramural.

The sacral part of the parasympathetic nervous system is represented by the pelvic nodes, scattered throughout the visceral plexuses of the pelvis. Preganglionic fibers originate from the sacral parasympathetic nuclei of the II-IV sacral segments of the spinal cord, emerge from them as part of the anterior roots of the spinal nerves and branch from them in the form of the pelvic splanchnic nerves. They form a plexus around the pelvic organs (rectum and sigmoid colon, uterus, fallopian tubes, vas deferens, prostate, seminal vesicles).

In addition to the sympathetic and parasympathetic nervous systems, the existence of a metasympathetic nervous system has been proven. It is represented by nerve plexuses and microscopic nodes in the walls of hollow organs that have motility (stomach, small and large intestines, bladder, etc.). These formations differ from parasympathetic mediators (purine bases, peptides, gamma-aminobutyric acid). The nerve cells of the metasympathetic nodes are capable of generating nerve impulses without the participation of the central nervous system and sending them to smooth myocytes, causing movement of the organ wall or part of it.

Rice. 19. Structure of the parasympathetic division of the autonomic nervous system (S.V. Savelyev, 2008)

Sympathetic department in its main functions it is trophic. It provides increased oxidative processes, increased respiration, increased heart activity, i.e. adapts the body to conditions of intense activity. In this regard, the tone of the sympathetic nervous system predominates during the day.

Parasympathetic Division performs a protective role (constriction of the pupil, bronchi, decreased heart rate, emptying of the abdominal organs), its tone predominates at night (“the kingdom of the vagus”).

The sympathetic and parasympathetic departments also differ in mediators - substances that transmit nerve impulses at synapses. The mediator in sympathetic nerve endings is norepinephrine. Mediator of parasympathetic nerve endings - acetylcholine.

Along with the functional ones, there are a number of morphological differences in the sympathetic and parasympathetic divisions of the autonomic nervous system, namely:

The parasympathetic centers are separated and are located in three sections of the brain (mesencephalic, bulbar, sacral), and the sympathetic centers are located in one (thoracolumbar section).

The sympathetic nodes include nodes of the 1st and 2nd order, and the parasympathetic nodes include the 3rd order (terminal). In this connection, preganglionic sympathetic fibers are shorter, and postganglionic fibers are longer than parasympathetic.

The parasympathetic division has a more limited area of ​​innervation, innervating only internal organs. The sympathetic department innervates all organs and tissues.

Sympathetic division of the autonomic nervous system

Sympathetic nervous system consists of central and peripheral sections.

Central department represented by the intermediate-lateral nuclei of the lateral horns of the spinal cord of the following segments: W 8, D 1-12, P 1-3 (thoracolumbar region).

Peripheral department The sympathetic nervous system consists of:

nodes of the 1st and 2nd order;

internodal branches (between the nodes of the sympathetic trunk);

the connecting branches are white and gray, associated with the nodes of the sympathetic trunk;

visceral nerves, consisting of sympathetic and sensory fibers and heading to the organs, where they end in nerve endings.

THE SYMPATHETIC TRUNK, paired, is located on both sides of the spine in the form of a chain of first-order nodes. IN longitudinal direction nodes are connected to each other by internodal branches. In the lumbar and sacral regions there are also transverse commissures that connect the nodes of the right and left sides. The sympathetic trunk extends from the base of the skull to the coccyx, where the right and left trunks are connected by one unpaired coccygeal node. Topographically, the sympathetic trunk is divided into 4 sections: cervical, thoracic, lumbar and sacral.

The nodes of the sympathetic trunk are connected to the spinal nerves by white and gray communicating branches.

White connecting branches consist of preganglionic sympathetic fibers, which are axons of the cells of the intermediolateral nuclei of the lateral horns of the spinal cord. They are separated from the spinal nerve trunk and enter the nearest nodes of the sympathetic trunk, where part of the preganglionic sympathetic fibers are interrupted. The other part passes through the node in transit and through the internodal branches reaches more distant nodes of the sympathetic trunk or passes to nodes of the second order.

Sensitive fibers, the dendrites of the cells of the spinal ganglia, also pass through the white connecting branches.

The white connecting branches go only to the thoracic and upper lumbar nodes. Preganglionic fibers enter the cervical nodes from below from the thoracic nodes of the sympathetic trunk through the internodal branches, and into the lower lumbar and sacral nodes - from the upper lumbar nodes also through the internodal branches.

From all nodes of the sympathetic trunk, part of the postganglionic fibers joins the spinal nerves - gray connecting branches and as part of the spinal nerves, sympathetic fibers are directed to the skin and skeletal muscles in order to ensure the regulation of its trophism and maintain tone - this somatic part sympathetic nervous system.

In addition to the gray connecting branches, visceral branches depart from the nodes of the sympathetic trunk for innervation internal organs - visceral part sympathetic nervous system. It consists of: postganglionic fibers (cell processes of the sympathetic trunk), preganglionic fibers that passed through the first order nodes without interruption, as well as sensory fibers (cell processes of the spinal nodes).

Cervical region The sympathetic trunk most often consists of three nodes: upper, middle and lower.

U p p e r cervical node lies in front of the transverse processes of the II-III cervical vertebrae. The following branches depart from it, which often form plexuses along the walls of blood vessels:

Internal carotid plexus(along the walls of the artery of the same name ) . The deep petrosal nerve departs from the internal carotid plexus to innervate the glands of the mucous membrane of the nasal cavity and palate. A continuation of this plexus is the plexus of the ophthalmic artery (for the innervation of the lacrimal gland and the muscle that dilates the pupil ) and plexus of cerebral arteries.

External carotid plexus. Due to secondary plexuses along the branches of the external carotid artery salivary glands are innervated.

Laryngopharyngeal branches.

Superior cervical cardiac nerve

MIDDLE cervical node located at the level of the VI cervical vertebra. Branches extend from it:

Branches to the inferior thyroid artery.

Middle cervical cardiac nerve, entering the cardiac plexus.

LOWER NECK JOINT is located at the level of the head of the 1st rib and often merges with the 1st thoracic node, forming the cervicothoracic node (stellate). Branches extend from it:

Inferior cervical cardiac nerve, entering the cardiac plexus.

Branches to the trachea, bronchi, esophagus, which, together with the branches of the vagus nerve, form plexuses.

Thoracic region The sympathetic trunk consists of 10-12 nodes. The following branches depart from them:

Visceral branches depart from the upper 5-6 nodes to innervate the organs of the thoracic cavity, namely:

Thoracic cardiac nerves.

Branches to the aorta, forming the thoracic aortic plexus.

Branches to the trachea and bronchi, participating together with the branches of the vagus nerve in the formation of the pulmonary plexus.

Branches to the esophagus.

5. Branches extend from V-IX thoracic nodes, forming great splanchnic nerve.

6. From X-XI thoracic nodes - small splanchnic nerve.

The splanchnic nerves pass into the abdominal cavity and enter the celiac plexus.

Lumbar The sympathetic trunk consists of 4-5 nodes.

The visceral nerves depart from them - splanchnic lumbar nerves. The upper ones enter the celiac plexus, the lower ones enter the aortic and inferior mesenteric plexuses.

Sacral section The sympathetic trunk is represented, as a rule, by four sacral nodes and one unpaired coccygeal node.

They are moving away from them splanchnic nerves, entering the superior and inferior hypogastric plexuses.

PRESPINAL NODES AND AUTONOMIC PLEXUS

Prevertebral nodes (nodes of the second order) are part of the autonomic plexuses and are located in front of the spinal column. On the motor neurons of these nodes, preganglionic fibers end, passing through the nodes of the sympathetic trunk without interruption.

Autonomic plexuses are located mainly around blood vessels, or directly near organs. Topographically, the autonomic plexuses of the head and neck, chest, abdominal and pelvic cavities are distinguished. In the head and neck area, the sympathetic plexuses are located mainly around the vessels.

In the chest cavity, the sympathetic plexuses are located around the descending aorta, in the region of the heart, near hilus of the lung and along the bronchi, around the esophagus.

The most significant in the chest cavity is cardiac plexus.

In the abdominal cavity, sympathetic plexuses surround the abdominal aorta and its branches. Among them, the largest plexus is the celiac plexus (“brain of the abdominal cavity”).

Celiac plexus(solar) surrounds the beginning of the celiac trunk and the superior mesenteric artery. The plexus is bounded above by the diaphragm, on the sides by the adrenal glands, and below reaches renal arteries. The following take part in the formation of this plexus: nodes(second order nodes):

Right and left celiac ganglia semi-lunar shape.

Unpaired superior mesenteric ganglion.

Right and left aortorenal nodes, located at the point of origin of the renal arteries from the aorta.

These nodes receive preganglionic sympathetic fibers, which are switched here, as well as postganglionic sympathetic and parasympathetic and sensory fibers passing through them.

Participate in the formation of the celiac plexus nerves:

Greater and lesser splanchnic nerves, extending from the thoracic nodes of the sympathetic trunk.

Lumbar splanchnic nerves - from the upper lumbar nodes of the sympathetic trunk.

Branches of the phrenic nerve.

Branches of the vagus nerve, consisting predominantly of preganglionic parasympathetic and sensory fibers.

A continuation of the celiac plexus are secondary paired and unpaired plexuses along the walls of the visceral and parietal branches of the abdominal aorta.

The second most important element in the innervation of the abdominal organs is abdominal aortic plexus, which is a continuation of the celiac plexus.

Derived from the aortic plexus inferior mesenteric plexus, entwining the artery of the same name and its branches. Here is located

quite a large node. The fibers of the inferior mesenteric plexus reach the sigmoid, descending and part of the transverse colon. The continuation of this plexus into the pelvic cavity is the superior rectal plexus, which accompanies the artery of the same name.

The continuation of the abdominal aortic plexus downwards is the plexus of the iliac arteries and arteries lower limb, and unpaired superior hypogastric plexus, which at the level of the promontory is divided into the right and left hypogastric nerves, forming the inferior hypogastric plexus in the pelvic cavity.

In education inferior hypogastric plexus autonomic nodes of the second order (sympathetic) and third order (periorgan, parasympathetic), as well as nerves and plexuses participate:

1. Sternal sacral nerves- from sacral region sympathetic trunk.

2.Branches of the inferior mesenteric plexus.

3. Splanchnic pelvic nerves, consisting of preganglionic parasympathetic fibers - processes of the cells of the intermediate-lateral nuclei of the sacral spinal cord and sensory fibers from the sacral spinal ganglia.

PARASYMPATHETIC DIVISION OF THE AUTONOMIC NERVOUS SYSTEM

The parasympathetic nervous system consists of central and peripheral divisions.

Central department includes nuclei located in the brain stem, namely in the midbrain (mesencephalic region), pons and medulla oblongata (bulbar region), as well as in the spinal cord (sacral region).

Peripheral department presented by:

preganglionic parasympathetic fibers passing through the III, VII, IX, X pairs cranial nerves, as well as as part of the splanchnic pelvic nerves.

nodes of the third order;

postganglionic fibers that end on smooth muscle and glandular cells.

Parasympathetic part oculomotor nerve (IIIpair) represented by the accessory nucleus located in the midbrain. Preganglionic fibers go as part of the oculomotor nerve, approach the ciliary ganglion, located in the orbit, there they are interrupted and postganglionic fibers penetrate into eyeball to the muscle that constricts the pupil, ensuring the reaction of the pupil to light, as well as to the ciliary muscle, which affects the change in the curvature of the lens.

Parasympathetic part of the interfacial nerve (VIIpair) represented by the superior salivary nucleus, which is located in the pons. The axons of the cells of this nucleus pass as part of the intermediate nerve, which joins facial nerve. In the facial canal, parasympathetic fibers are separated from the facial nerve in two portions. One portion is isolated in the form of a large petrosal nerve, the other in the form of a tympanic chord.

Greater petrosal nerve connects with the deep petrosal nerve (sympathetic) and forms the nerve of the pterygoid canal. As part of this nerve, preganglionic parasympathetic fibers reach the pterygopalatine ganglion and end on its cells.

Postganglionic fibers from the node innervate the glands of the mucous membrane of the palate and nose. A minority of postganglionic fibers reach the lacrimal gland.

Another portion of preganglionic parasympathetic fibers in the composition drum string joins the lingual nerve (from the III branch trigeminal nerve) and as part of its branches approaches the submandibular node, where they are interrupted. The axons of ganglion cells (postganglionic fibers) innervate the submandibular and sublingual salivary glands.

Parasympathetic part of the glossopharyngeal nerve (IXpair) represented by the inferior salivary nucleus located in the medulla oblongata. Preganglionic fibers emerge as part of the glossopharyngeal nerve, and then its branches - tympanic nerve, which penetrates tympanic cavity and forms the tympanic plexus, which innervates the glands of the mucous membrane of the tympanic cavity. Its continuation is lesser petrosal nerve, which exits the cranial cavity and enters the auricular ganglion, where the preganglionic fibers are interrupted. Postganglionic fibers are directed to the parotid salivary gland.

Parasympathetic part of the vagus nerve (Xpair) represented by the dorsal nucleus. Preganglionic fibers from this nucleus, as part of the vagus nerve and its branches, reach the parasympathetic nodes (III

order), which are located in the wall of internal organs (esophageal, pulmonary, cardiac, gastric, intestinal, pancreas, etc. or at the gates of organs (liver, kidneys, spleen). The vagus nerve innervates the smooth muscles and glands of the internal organs of the neck, thoracic and abdominal cavity to the sigmoid colon.

Sacral division of the parasympathetic part of the autonomic nervous system represented by the intermediate-lateral nuclei of the II-IV sacral segments of the spinal cord. Their axons (preganglionic fibers) leave the spinal cord as part of the anterior roots, and then the anterior branches of the spinal nerves. They are separated from them in the form pelvic splanchnic nerves and enter the inferior hypogastric plexus to innervate the pelvic organs. Some preganglionic fibers have an ascending direction to innervate the sigmoid colon.

Sympathetic nervous system (from Greek sympathes - sensitive, susceptible to influence)

part of the autonomic nervous system of vertebrate animals and humans, consisting of sympathetic centers, right and left border sympathetic trunks located along the spine, ganglia (nodes) and nerve branches connecting the ganglia with each other, with the spinal cord and with effectors (See Effectors). The border sympathetic trunk is a chain of ganglia connected by internodal commissures; lies (right or left) on the vertebral bodies; each ganglion is also connected to one of the spinal nerves (See Spinal nerves). Fibers S. n. With. innervate all organs and tissues of the body without exception. Centers of S. science With. located in the thoracic and lumbar segments of the spinal cord. The sympathetic nuclei that form the lateral horns of the gray matter of the spinal cord are present only in 15-16 segments (from the last cervical or 1st thoracic to the 3rd lumbar segment). These nuclei are considered as a working apparatus, subordinate to suprasegmental formations, which are localized in the medulla oblongata (See Medulla oblongata) and the Hypothalamus, controlled by the cerebral cortex. A special place in the physiology of S. n. With. and coordination of the processes controlled by it is occupied by the Cerebellum. S. N. With. - efferent system that conducts impulses to various internal organs. Most authors deny the existence of their own afferent fibers in S. n. With. However, a number of works provide evidence of their existence. In the abdominal cavity, the fibers of S. n. With. pass as part of the greater, lesser and lumbar splanchnic nerves. Afferent nerves that conduct impulses from internal organs are represented in the cerebral cortex and subcortical ganglia. Sympathetic nerve impulses from the central nervous system to the executive organs follow a two-neuron pathway. The first neuron is located in the lateral horns of the spinal cord. The axons (processes) of the first neuron (preganglionic fibers) leave the spinal cord through the ventral roots of the corresponding segments and enter the mixed spinal nerves, from which, as part of the white connecting branches, they reach the corresponding node of the border sympathetic trunk, where some of the fibers end in synapses (See Synapses) on effector neurons; in this case, each preganglionic fiber is in contact with a large number nerve cells (up to 30). Another part of the preganglionic fibers passes through the nodes of the borderline sympathetic trunk, without ending on its cells, and together with other fibers forms a number of nerves: the greater and lesser celiac, the lumbar celiac, entering the prevertebral sympathetic nodes. Some preganglionic fibers pass without interruption through these nodes, reaching the working organ, in nerve nodes the walls of which they take a break. The second effector neuron is located in the peripheral sympathetic ganglia, its processes (postganglionic fibers) enter the innervated organ. The second neuron is located in the perivertebral (paravertebral) ganglia or in the prevertebral (prevertebral) ganglia (solar plexus nodes, inferior mesenteric node and others located at a great distance from the central nervous system, near internal organs). Postganglionic fibers enter the spinal nerve through the gray connecting branches, and in its composition they reach the innervated organ. Consequently, a break in each efferent sympathetic pathway in the arc that closes in the spinal cord occurs only once: either in the node of the border sympathetic trunk, or in nodes distant from the spine. Along with the sympathetic arc, which closes in the spinal cord, there are also short sympathetic reflex arcs, which close in the peripheral sympathetic ganglia (solar plexus, caudal mesenteric).

The speed of excitation in sympathetic pre- and especially postganglionic fibers is many times lower than in somatic, i.e., bodily, and is about 1-3 m/sec. To cause effects in sympathetic fibers, a significantly greater force of stimulation is required. Originating in S. science. With. excitation, as a rule, involves a large number of neurons, so the effects of stimulation are not localized in any specific organ, but cover wide areas. The reactions that follow in response to irritation of sympathetic fibers are characterized by a relatively slow and prolonged nature, as well as a slow, prolonged attenuation of the ongoing processes. A number of substances (ganglionic blockers, ergot preparations) suppress the effects of stimulation of S. n. With. Some chemicals have the same effect on organs and tissues as irritation of the sympathetic nerves. This is due to the fact that when the sympathetic nerves are irritated, substances of similar action are released by the terminal formations of postganglionic sympathetic fibers (see Mediators). In the endings of all preganglionic fibers, as well as postganglionic, innervating sweat glands, the mediator Acetylcholine is formed, in the endings of postganglionic fibers (with the exception of those innervating the sweat glands) - Norepinephrine. The influence of the sympathetic and parasympathetic nervous systems (See Parasympathetic nervous system) on the activity of an organ is often opposite. When irritating sympathetic fibers innervating various organs, typical effects occur: acceleration and intensification of heart contractions, dilation of the pupil and mild lacrimation, contraction of smooth muscle fibers (pilomotors) that raise hair, secretion of sweat glands, poor secretion thick saliva And gastric juice, inhibition of contractions and weakening of the tone of the smooth muscles of the stomach and intestines (excluding the area of ​​the ileocecal sphincter), muscle relaxation Bladder and inhibition of contractions of the obturator sphincter, expansion coronary vessels heart, narrowing of the small arteries of the abdominal organs and skin, small arteries of the lungs and brain, changes in the excitability of receptors, as well as various departments central nervous system, increasing the strength of contractions of the tired skeletal muscle, increasing its excitability and changing its mechanical properties.

Neurons S. n. s., affecting executive bodies, are in a state of constant tonic excitation as a result of the interaction of unconditioned and conditioned reflexes carried out by the higher parts of the central nervous system. Tonic impulses S. n. With. extremely important for maintaining consistency internal environment body (Homeostasis a). Through sympathetic fibers and centers, a reflex relationship between all internal organs is ensured. Reflexes involving the action of S. n. pp., can occur due to irritation of both visceral and somatic nerves. Thus, with viscero-visceral reflexes, excitation arises and ends in the internal organs (irritation of the peritoneum causes a slowdown in cardiac activity). With visceromotor reflexes, excitation from the internal organs passes to the skeletal muscles (irritation of the peritoneum increases the tone of the abdominal muscles). Animals with completely removed border sympathetic trunks and ganglia (desympathized) outwardly differ little from normal ones, however, under certain loads (muscular work, cooling, etc.) they are less hardy. This indicates that S. n. s., exerting on functional state tissues have a regulating effect, adapting (adapting) them to perform functions under given conditions (see Adaptive-trophic function). S. N. With. Stimulates mainly processes associated with the release of energy in the body and vigorous activity. Physiological manifestations of emotions (See Emotions) are associated primarily with the excitement of S. n. With.

A. D. Nozdrachev.

Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

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