Sympathetic nervous system

The sympathetic nervous system (pars sympathica) includes:

1. lateral intermediate (gray) matter (vegetative core) in the lateral (intermediate) columns of the spinal cord from VIII cervical segment (CVIII) II lumbar (LII);
2. sympathetic nerve fibers and nerves coming from the cells of the lateral intermediate substance (lateral column) to the nodes of the sympathetic trunk and the vegetative plexuses of the abdominal cavity and pelvis;
3. right and left sympathetic trunks;
4. connecting branches connecting spinal nerves (СVIII-ThI-LII) with sympathetic trunk and sympathetic trunk with all cerebrospinal nerves;
5. nodes of vegetative nerve plexuses located anterior to the spine in the abdominal cavity and pelvic cavity, and nerves lying in the walls of large vessels (circumvascular plexus);
6. nerves moving from these plexuses to organs;
7. sympathetic fibers that go in the somatic nerves to organs and tissues. Sympathetic preganglionic nerve fibers are usually shorter than postganglionic fibers.

Neurons are present in the thoracic and upper lumbar spinal cord, their axons are the preganglionic fibers that come out with the front roots and approach the sympathetic trunk. Preganglionic fibers are also called white connective fibers, since they have a larger myelin liner than postganglionic ones. The most important sympathetic formation is the sympathetic trunk, also referred to as the "sympathetic chain" located on either side of the spine (hence another name - paravertebral nodes). There are 20-22 nodes in the trunk: 3 cervical (the middle is sometimes poorly represented, and the lower one, often united with the first thoracic node, forms a powerful star knot), 10-12 thoracic, 3-4 abdominal and 4 pelvic. In the ganglia there are three types of cells, differing in magnitude: large (35-55 microns in diameter), medium (25 32 microns) and small (15-22 microns). In different ganglia they are represented in unequal proportions. Thus, in the upper cervical ganglion, their number is 27, respectively; 50; 23%, in stellate less than large cells, but more than average (17, 67, 16%).

The preganglionic fibers that approach the ganglia are partially interrupted in the neurons of the nodes, in part, without interruption, go to the prevertebral ganglia. Vegetative fibers predominantly belong to groups B and C; the most thick fibers, myelin-rich fiber, 5-6.5 microns in diameter (type A), are rarely observed. The degree of myelination determines the rate of excitation. The highest speed is achieved when the thick fiber interacts with the dendrite of a large cell. Fibers of one neuron can approach several neighboring nodes of the chain (up to 8 knots). For the rate of excitation, an important role is played by the fact that the preganglionic fiber interacts with one neuron (high speed) or several (pluricellular innervation), while the rate of excitation is slowed. The "one-to-one" transmission is rare. It is possible to observe both the phenomena of spatial summation (when the reaction to stimulation of two preganglionic nerves exceeds the sum of the responses when they are separately stimulated), and the phenomenon of occlusion, or suppression, when the discharge of postganglionic fiber is less than the sum of the stimulation of several preganglionic nerves. After passing through the sympathetic trunk, the fibers are designated as postganglionic, or gray, connective fibers, having an average of a smaller value than the preganglionic fibers.

Postganglionic fibers from the upper cervical node along with the carotid artery are directed to the brain and face, from the stellate node in the form of plexus arteries, the postganglionic fibers (also known as the Frank nerve) innervate the cerebral vessels that make up the pool of the vertebral artery.

Fibers passed through the thoracic, ventral and pelvic nodes, rush to the next switching station - the prevertebral nodes or plexuses. In contrast to the sympathetic trunk, the cellular composition of this formation is more uniform and is mainly represented by neurons of medium size. The most famous node, which is also one of the most important, is called solar, and sometimes celiac, plexus, or "abdominal brain." It consists of two nodes (left and right). In the prevertebral nodes, sympathetic fibers (that go into the celiac nerve) are interrupted, and the sympathetic chain does not have contact with the neurons, and parasympathetic neurons also appear (paravertebral nodes are purely sympathetic).

After passing through the prevertebral nodes located in the abdominal cavity or small pelvis, the vegetative fibers approach either directly to the innervated tissues (in these cases they are thin nerve fibers that release a chemical that exerts a diffusion effect on the tissues-diffusion synapses), or to the ganglia located in the organs themselves (such intramural ganglia are present in the heart, gastrointestinal tract and other organs).

Sympathetic trunk

The sympathetic trunk (tnincus sympathicus) is a paired formation located on the sides of the spine. It consists of 20-25 nodes connected by interstitial branches (rr. Interganglionares). The nodes of the sympathetic trunk (ganglia trunci sympathici) are spindle-shaped, ovoid and irregular (polygonal) in shape. Only one type of branch is suitable for the sympathetic trunk - the so-called white connecting branches (r. Communicantes albi). From the sympathetic trunk there are four types of branches:

• gray connective branches (r. Communicantes grisei) to spinal nerves;
• sympathetic nerves to internal organs;
• sympathetic nerves to the blood vessels;
• sympathetic nerves (celiac) to large vegetative plexuses located in the abdominal cavity and in the pelvic cavity.

A white connective branch is a bundle of preganglionic nerve fibers branching from the spinal nerve (at the level of the thoracic and upper lumbar regions) and entering the sympathetic trunk located nearby. In the white connective branches there are preganglionic sympathetic nerve fibers, which are the processes of the neurons of the lateral intermediate columns of the (autonomous) spinal cord. These fibers pass through the anterior horns of the spinal cord and come out of it in the composition of the anterior roots, and then go in the spinal nerves, from which branch off the exit of these nerves from the spinal holes. White connective branches are present only in VIII cervical, all thoracic and two upper lumbar spinal nerves and are suitable for all thoracic (including cervicothoracic) and the two upper lumbar nodes of the sympathetic trunk. To the cervical, lower lumbar, sacral and coccygeal nodes of the sympathetic trunk, preganglionic fibers enter the inter-node branches of the sympathetic trunk.

From the nodes of the sympathetic trunk, gray connective branches extend all the way to the nearest spinal cord. Gray connective branches contain postganglionic sympathetic nerve fibers - the processes of cells lying in the nodes of the sympathetic trunk. In the spinal nerves and their branches, these postganglionic sympathetic fibers are directed to the skin, muscles, all organs and tissues, the blood and lymphatic vessels, the sweat and sebaceous glands, to the muscles that lift the hair, and carry out their sympathetic innervation. From the sympathetic trunk, in addition to the gray connective branches, nerves flow to the internal organs and vessels (cardiac, esophageal, aortic, etc.). These nerves also contain postganglionic sympathetic fibers. In addition, from the sympathetic trunk, the sympathetic nerves that follow the nodes of the vegetative plexus of the abdominal cavity and pelvis, containing preganglionic fibers that have passed through the nodes of the sympathetic trunk, depart. Topographically, four sympathetic trunks are distinguished: cervical, thoracic, lumbar, sacral (pelvic).

The cervical region of the sympathetic trunk is represented by three nodes and interconnected branches, which are located on the deep neck muscles behind the prevertebral plate of the cervical fascia. To the cervical nodes, preganglionic sympathetic fibers approach the interstitial branches of the thoracic sympathetic trunk, where they come from the vegetative nuclei of the lateral intermediate (gray) substance VIII of the cervical and six to seven upper thoracic segments of the spinal cord.

The upper cervical node (ganglion cervicale superius) is the largest node of the sympathetic trunk. It is fusiform, its length reaches 2 cm or more (up to 10 cm), thickness - up to 0.5 cm. The upper cervical node is located in front of the transverse processes of I-III cervical vertebrae. In front of the node are the internal carotid artery, the initial part of the vagus nerve, behind - the long muscle of the head. From the upper cervical sympathetic node depart the following branches containing postganglionic sympathetic fibers: gray connective branches, internal carotid nerve, external carotid nerves, jugular nerve, laryngeal-pharyngeal branches, upper cervical cord nerve.

1. Gray connective branches (r. Communicantes grisei) go to the cervical spinal nerves.
2. The internal carotid nerve (n. Sacroticus inteirms) is sent to the same artery and along the way forms the internal carotid plexus (plexus caroticus interims). Together with the internal carotid artery this plexus enters the sleep canal, and then into the cavity of the skull. In the sleepy canal, the drowsy nerves to the mucous membrane of the middle ear depart from the plexus. After the exit of the internal carotid artery, a deep stony nerve (n. Petrosus profundus) separates from the inner carotid plexus. It passes through the fibrous lag of the lacerated hole and enters the pterygoid canal of the sphenoid bone, where it joins with the large stony nerve, forming the nerve of the pterygoid canal (n. Canalis pterygoidei). The nerve of the pterygoid canal (more prominently the nerve), entering the pterygoid-palatine fossa, joins the pterygoid node. After passing through the pterygoid node, the sympathetic fibers along the pterygoid nerves pass into the maxillary nerve and spread in the composition of its branches, realizing the sympathetic innervation of the vessels, tissues, glands of the oral mucosa and nasal cavity, conjunctiva of the lower eyelid and skin of the face. In the orbit, sympathetic fibers fall into the form of the periarterial plexus of the eye artery - the branch of the internal carotid artery. From the eye plexus, the sympathetic root spurs to the ciliary node. Fibers of this root pass through the ciliary unit and in the composition of short ciliary nerves reach the eyeball, where the vessels of the eye innervate and the muscle that dilates the pupil. In the cranial cavity, the inner carotid plexus continues into the surrounding-vascular plexus of the branches of the internal carotid artery.
3. External carotid nerves (nn. Carotici externi) in the form of 2-3 trunks are directed to the external carotid artery and form the same-named sympathetic plexus (plexus carotici externus) along its course. The external carotid plexus spreads along branches of the same artery, carrying out sympathetic innervation of vessels, glands, smooth muscle elements and tissues of the head organs. The internal carotid plexus (plexus carotici intenuis) is located in the adventitia of the eponymous artery. The sympathetic fibers of this plexus along the branches of this artery are directed to the innervated organs.
4. The jugular nerve (n. Jugularis) rises along the walls of the internal jugular vein to the jugular opening, where it divides into branches leading to the upper and lower nodes of the glossopharyngeal nerve and to the hyoid nerve. Due to this sympathetic fibers are distributed in the composition of the branches of IX, X and XII cranial nerves.
5. The throat-pharyngeal branches (r. Laryngopharyngei) participate in the formation of the laryngeal-pharyngeal plexus, innervate the vessels, mucous membrane of the pharynx and larynx, muscles and other tissues.
6. The superior cervical cardiac nerve (n. Cardiacus cervicalis superior) descends parallel to the sympathetic trunk anterior to the pre-vertebral plate of the cervical fascia. The right upper cardiac nerve passes along the brachiocephalic trunk and enters the deep part of the cardiac plexus on the posterior surface of the aortic arch. The left upper cervical cardiac nerve lies to the left common carotid artery, enters the superficial part of the cardiac plexus located between the arch of the aorta and the bifurcation of the pulmonary trunk.

The middle cervical node (ganglion cervicale medium) is unstable, located anterior to the transverse process of the sixth cervical vertebra. Most often this site is located at the intersection of the cervical sympathetic trunk and the lower thyroid artery. The length of the node is 0.75-1.5 cm, the thickness is about 0.4-0.5 cm. The node has an ovoid or triangular shape. The middle cervical node is connected to the upper cervical node with one interstitial branch, and with the cervicothoracic (stellate) node - two or three interstitial branches. One of these branches passes in front of the subclavian artery, the other behind, forming a subclavian loop (ansa subclavian or Viestan loop.

From the average sympathetic node, gray connective branches branch out to the V and VI cervical spinal nerves, the middle cervical cardiac nerve (n. Cardiacus cervicalis medius). This nerve goes lateral to the upper cervical cardiac nerve. The right middle cervical cord nerve is located along the brachiocephalic trunk, and the left one - along the left common carotid artery. Both nerves enter the deep part of the heart plexus. From the middle cervical node depart two or three thin nerves, which are involved in the formation of a common carotid plexus and plexus of the lower thyroid artery, innervate the thyroid and parathyroid glands. In the absence of an average cervical node, all these branches branch from the interstitial branches at the level of the transverse process of the sixth cervical vertebra, and the post-nodal sympathetic fibers in these branches fall from the cervicothoracic node.

The cervico-thoracic (stellate) node (ganglion cervicothoracicum) lies behind the subclavian artery, at the site of the vertebral artery from it. This node was formed as a result of the fusion of the lower cervical node with the first thoracic node. The cervico-thoracic node is flattened in anteroposterior direction, has an irregular (stellate) shape, its diameter is on average 8 mm.

A number of branches leave the node:

1. Gray connective branches (r. Communicantes grisei) are directed to the VI, VII, VIII cervical spinal nerves.
   Several stem cells retreat to the subclavian artery, in the adventitia of which form the subclavian plexus (plexus subclavicus), continuing on the vessels of the shoulder girdle and upper limb.

Several sympathetic branches join the vagus nerve and its branches, as well as to the diaphragmatic nerve.

2. The vertebral nerve (n. Vertebralis) approaches the vertebral artery and participates in the formation of the sympathetic vertebral plexus (plexus vertebralis), from which the vessels of the brain and spinal cord are innervated. The lower cervical cardiac nerve (n. Cardiacus cervicalis inferior) on the right passes behind the brachiocephalic trunk, and to the left - behind the aorta. The right and left cervical cardiac nerves enter the deep part of the heart plexus.

The thoracic region of the sympathetic trunk includes 9-12 thoracic nodes (ganglia thoracica), flattened, fusiform or polygonal. Sizes of knots from 1 to 16 mm, on average 3-5 mm. Upper thoracic nodes to the level of the VI thoracic vertebra are located in the intercostal spaces along the line of the rib head. In the lower thoracic region, the nodes are located on the lateral surface of the vertebral bodies. The thoracic region of the sympathetic trunk is covered with an intrathoracic fascia and a parietal pleura. Behind the sympathetic trunk in the transverse direction are the posterior intercostal vessels. To the thoracic nodes of the sympathetic trunk, white connective branches containing preganglionic sympathetic fibers approach from all the thoracic spinal nerves. In turn, from the thoracic nodes of the sympathetic trunk, several types of branches depart.

Gray connective branches containing postganglionic sympathetic fibers attach to a number of underlying spinal nerves.

Thoracic cardiac nerves (nn. Cardiaci thoracici) depart from the second to fifth thoracic nodes, are directed forward and medially, participate in the formation of the heart plexus.

Thin sympathetic nerves (pulmonary, esophageal, aortic) depart from the thoracic nodes of the sympathetic trunk, which together with the branches of the vagus nerve form the right and left pulmonary plexus (plexus pulmonalis), the esophageal plexus (plexus oesophagealis), the thoracic aortic plexus (plexus aorticus thoracicus). The branches of the thoracic aortic plexus continue to intercostal vessels and other branches of the thoracic aorta, forming periarterial plexuses on their way. Sympathetic nerves also extend to the walls of the unpaired and semi-unpaired veins, the thoracic duct and participate in their innervation. The largest branches of the sympathetic trunk in the thoracic region are the large and small internal nerves.

The large thoracic internal nerve (n. Splanchnicus thoracicus major) is formed from several branches extending from 5-10 thoracic nodes of the sympathetic trunk. The common trunk of the large thoracic inner nerve is directed downward and medially, is attached to the bodies of the lower thoracic vertebrae, then penetrates into the abdominal cavity between the muscle bundles of the lumbar part of the diaphragm next to the unpaired vein on the right and the semi-unpaired on the left and ends at the nodes of the celiac plexus. At the level of the XII thoracic vertebra in the course of the large thoracic internal nerve there is a small thoracic internal node (ganglionthoracicus splanchnicum).

The small thoracic inner nerve (n. Splanchnicus thoracicus minor) begins with branches extending from the X-XI, sometimes the XII node of the thoracic part of the sympathetic trunk. The nerve descends lateral to the large thoracic internal nerve, passes between the muscle beams of the lumbar part of the diaphragm (along with the sympathetic trunk). Part of the fibers of this nerve ends in the aortic nodule of the celiac plexus.

Large and small thoracic internal nerves are represented mainly by preganglionic sympathetic fibers, they also contain a certain amount of postganglionic fibers. In the composition of these celiac nerves, there are sensitive fibers that impart impulses from the internal organs to the spinal cord.

Next to the small thoracic inner nerve is the unstable lower thoracic internal nerve (n. Splanchnicus thoracicus imus), starting from the XII (sometimes XI) thoracic node of the sympathetic trunk and ending in the renal plexus.

The lumbar region of the sympathetic trunk is represented more often 3-5 (from 2 to 7) by the lumbar nodes and the inter-junction branches connecting them.

Lumbar nodes (ganglia lumbalia) are fusiform, their size does not exceed 6 mm. The nodes are located on the anterolateral surface of the bodies of the lumbar vertebrae, medial to the large lumbar muscle, and are covered by the intra-abdominal fascia. To the lumbar nodes of the right sympathetic trunk in front of the lower hollow vein. The nodes of the left trunk adjoin the left side of the abdominal part of the aorta. The lumbar nodes of the right and left sympathetic trunks are connected by transversely oriented connecting branches lying on the anterior surface of the lumbar vertebrae behind the aorta and inferior vena cava.

From each lumbar node there are two types of branches:

1. gray connective branches containing postganglionic sympathetic fibers, directed towards the lumbar spinal nerves;
2. lumbar internal nerves (nn. Splanchnici lumbales), which have both preganglionic and postganglionic sympathetic nerve fibers, directed towards the celiac plexus and organ (vascular) vegetative plexuses (splenic, renal, gastric, adrenal).

The sacral section of the sympathetic trunk is formed by four sacral spindle-shaped nodes about 5 mm in size, connected by interstitial branches. Sacral nodes (ganglia sacralia) lie on the pelvic surface of the sacrum, medially from the pelvic apertures. Below the right and left sympathetic trunks approach and end on the anterior surface of the sacrum common for these trunks unpaired node. In the pelvic cavity anterior rectum is located anterior to the sacral sympathetic nodes, separated from them by a layer of fatty tissue and a parietal leaf of the pelvic fascia. As in the lumbar region, there are transverse connections between the nodes of the sympathetic trunks of the right and left sides.

From the sacral nodes there are three types of branches:

1. gray connecting branches, in which the post-nodal sympathetic fibers are directed to the sacral and coccygeal spinal nerves and further - in the region where these nerves branch;
2. sacral internal nerves (nn. Splanchnici sacrales), which follow the upper and lower hypogastric (pelvic) vegetative plexuses;
3. organ branches leading to the organ and vascular plexus of the pelvis.