Sympathetic trunk: structure and function

The sympathetic nerve trunk is one of the components of the nervous peripheral part of the sympathetic system.

Structure

In accordance with the structure of the sympathetic trunk (Truncus sympathicus), it is paired and represents nodes that are connected to each other via sympathetic fibers. The data of education are located on the sides of the spine throughout its entire length.

Any of the nodes of the sympathetic trunk is a clump of vegetative neurons that switch the preganglionic fibers (most of them) that come out of the spinal cord, forming connecting white branches.

The above-described fibers contact the cells of the corresponding node or go in the interstitial branches to the lower or upper sympathetic trunk node.

There are connective white branches in the upper lumbar and thoracic areas. In the sacral, inferior lumbar and cervical nodes, branches of this type are absent.

In addition to the white branches, the connecting gray branches are also distinguished, which consist in the majority of sympathetic postganglionic fibers and connect the spinal nerves with the nodes of the trunk. Such branches go to each of the spinal nerves, moving away from each of the nodes of the sympathetic trunk. As part of the nerves they are sent to innervated organs (glands, smooth and striated muscles).

In the sympathetic trunk (anatomy) conditionally the following departments are distinguished:

1. Sacral.
2. Lumbar.
3. Thoracic.
4. Cervical.

Functions

In accordance with the sympathetic trunk and its constituent ganglia and nerves, several functions of this anatomical formation can be distinguished:

1. Innervation of the neck and head, as well as control over the reduction of blood vessels, their nourishing.
2. The innervation of the thoracic cavity organs (branches from sympathetic trunk nodes are included in the nerves in the pleura, diaphragm, pericardium and ligament of the liver).
3. The innervation of the vascular walls (as part of the nervous plexuses) of the common carotid, thyroid and subclavian arteries, as well as the aorta.
4. They connect the nervous ganglia with the nerve plexuses.
5. They participate in the formation of the celiac, aortic, upper-bicephalic and renal plexuses.
6. Innervation of the pelvic organs due to the entry of branches from the cranial ganglia of the sympathetic trunk into the composition of the lower hypogastric plexus.

Neck section of sympathetic trunk

In the cervical region there are three nodes: the lower, middle and upper. More details each of them will be considered further.

Top node

Formation of spindle-shaped size 20 * 5 mm. It is located on 2-3 cervical vertebrae (their lateral outgrowths) under the pre-invertebrate fascia.

It departs from the node seven main branches that carry postganglionic fibers, innervating the organs of the neck and head:

• Connecting gray branches to 1, 2, 3 spinal cervical nerves.
• N. jugularis (the jugular nerve) is divided into several branches, two of which are connected to the lingopharyngeal and vagus nerves, and one to the hyoid nerve.
• N. caroticus internus enters the outer shell of the internal carotid artery and forms there the same plexus, from which the sympathetic fibers in the area of the artery enter the eponymous canal on the temporal bone, forming a stony deep nerve passing along the wing canal in a wedge bones. After leaving the canal, the fibroids pass through the pterygoid fossa and join the parasympathetic postganglionic nerves from the ctenophoreal node, as well as the maxillary nerve, after which they are sent to the organs in the area of the face. In the sleepy canal from the sleepy inner plexus, branches are separated that penetrate and form a plexus in the tympanum. Inside the skull, the drowsy (internal) plexus passes into the cavernous, and its fibers spread through the vessels of the brain, forming the intertwining of the ocular, middle cerebral and anterior cerebral arteries. In addition, the cavernous plexus gives off branches that connect with the parasympathetic fibers of the parasympathetic ciliary node and innervate the muscle dilating the pupil.
• N. caroticus externus (sleepy external nerve). It forms an external plexus near the eponymous artery and its branches, which blood supply the organs of the neck, face and hard shell of the brain.
• The pharyngeal larynx branches accompany the vessels of the pharyngeal wall and form a pharyngeal plexus.
• The nerve of the upper heart passes near the cervical site of the sympathetic trunk. In the chest cavity forms a superficial cardiac plexus, which is located under the aortic arch.
• Branches that are part of the diaphragmatic nerve. Their endings are located in the capsule and ligaments of the liver, pericardium, parietal diaphragmatic peritoneum, diaphragm and pleura.

Medium Node

Education size 2 * 2 mm, located at the level of 4 cervical vertebra, in a place where the common carotid and lower thyroid arteries intersect. This node gives rise to four types of branches:

1. Connecting gray branches that go to 5, 6 spinal nerves.
2. The nerve is a middle heart, which is located behind the carotid joint artery. In the breast cavity, the nerve participates in the formation of the heart plexus (deep), which is located between the trachea and the aortic arch.
3. Branches that participate in the organization of the nerve plexus subclavian, common carotid and thyroid lower arteries.
4. The interstitial branch, which connects with the cervical upper sympathetic node.

Lower node

Education is located behind the vertebral column and above the subclavian arteries. In rare cases, it combines with the first sympathetic breast node and is then called the stellate (cervicothoracic) node. The lower node gives rise to six branches:

1. Connective gray branches leading to 7, 8 spinal cervical nerves.
2. The branch going to the plexus vertebralis, spreading in the skull and forming the plexus of the cerebral posterior artery and the basilar plexus.
3. The nerve is lower than the heart, which lies to the left behind the aorta, and on the right - behind the brachiocephalic artery and participates in the formation of a deep cardiac plexus.
4. The branches that enter the diaphragmatic nerve, but do not form plexuses, but terminate in the diaphragm, pleura and pericardium.
5. Branches forming the plexus of the carotid joint artery.
6. Branches up to the subclavian artery.

Thoracic department

The thoracic sympathetic trunk includes ganglia thoracica (nodular nodes) - nerve formations of a triangular shape that lie on the costal necks on the sides of the thoracic vertebrae, under the intrathoracic fascia and parietal pleura.

From the thoracic ganglia 6 major groups of branches depart:

1. White connecting branches that branch off from the intercostal nerves (their anterior roots) and penetrate into the nodes.
2. The gray connecting branches emerge from the ganglia and are directed to the intercostal nerves.
3. Branches of the mediastinum. They originate from 5 sympathetic upper gangies and pass into the posterior mediastinum, together with other fibers forming the bronchial and esophageal plexus.
4. Nerves of the heart. They originate from 4-5 sympathetic upper ganglia, participating in the formation of the aortic and deep cardiac plexus.
5. The nerve is large. Collected from the branches of 5-9 sympathetic thoracic nodes and covered with an intrathoracic fascia. Through the holes between the intermediate and medial legs of the diaphragm, this nerve passes into the abdominal cavity and ends in the ganglia of the celiac plexus. The composition of this nerve includes a large number of preganglionic fibers (which switch in the ganglion of the celiac plexus to postganglionic fibers), and postganglionic fibers that have already switched at the level of the thoracic ganglia of the sympathetic trunk.
6. The nerve is small intrastinal. It is formed by 10-12 knots. Through the diaphragm, it descends slightly lateral to the n. Splanchnicus major and also enters the celiac plexus. Part of the preganglionic fibers of this nerve in the sympathetic ganglia are switched to postganglionic ganglia, and part follows to the organs.

Lumbar section

Lumbar ganglia of the sympathetic trunk is nothing more than the continuation of the chain of ganglia of the thoracic department. The lumbar division includes 4 nodes that are located on both sides of the spine on the inner edge of the large lumbar muscle. On the right side, the nodes are visualized outside of the vena cava inferior, and to the left - outside of the aorta.

The branches of the lumbar sympathetic trunk are:

1. White connecting branches extending from 1 and 2 spinal nerve spinal nerves and fitting to 1 and 2 ganglia.
2. Gray connecting branches. They combine the lumbar ganglia with all spinal lumbar spinal nerves.
3. The internal lumbar branches that extend from all the ganglia and enter the upper hypogastric, celiac, aortic abdominal, renal and superior mesenteric plexus.

Sacral Department

The lowest part (according to the topography of the sympathetic trunk) is the sacral section, which consists of one unpaired coccygeal node and four paired sacral ganglia. The nodes are slightly medial to the sacral anterior orifices.

There are several branches of the sacral segment of the sympathetic trunk:

1. Connecting the gray branches, going to the sacral and spinal nerves.
2. Nerves are internal, which are part of the vegetative plexus in the small pelvis. Visceral fibers from these nerves form a hypogastric lower plexus lying on the branches from the iliac internal artery, thanks to which the sympathetic nerves penetrate into the pelvic organs.