Human Anatomy and Physiology - N. I. Fedyukovich 2003

Nervous system
Autonomic (vegetative) nervous system
Sympathetic division of the autonomic nervous system

The sympathetic division consists of central and peripheral parts. The central part includes the lateral intermediate (gray) substance (autonomic Nucleus), which lies in the lateral columns from the VIII cervical to the II lumbar segments of the Spinal Cord. The peripheral part is formed by sympathetic preganglionic fibers emerging from these spinal segments, which travel within the anterior roots of the spinal cord and synapse in the paravertebral and prevertebral ganglia of the Sympathetic trunk.

The sympathetic trunk is a paired Structure consisting of 20—25 ganglia connected to each other by interganglionic branches. Each ganglion of the sympathetic trunk resembles a cluster of Cells of various sizes, surrounded by a Connective Tissue capsule, and has a fusiform, ovoid, or irregular (polygonal) shape. The ganglia of the sympathetic trunk are located on both sides of THE Vertebral Column, extending from the Base of the Skull to the coccyx. They connect to the Spinal Nerves via gray and white rami communicantes. The gray rami communicantes contain postganglionic sympathetic fibers, which are the processes of Neurons located within the ganglia of the sympathetic trunk. A common feature of the gray rami communicantes is their close association with Blood Vessels. Along these vessels, postganglionic sympathetic fibers within the spinal nerves travel to the Skin, Muscles, all Internal Organs, sweat and Sebaceous Glands, providing their innervation. The largest gray ramus communicans is the vertebral nerve, which is a branch of the cervicothoracic sympathetic trunk running to the vertebral artery.

White rami communicantes are found only in the thoracic and lumbar Regions of the sympathetic trunk at the level of the CVIII - LIII spinal cord segments, which contain segmental sympathetic centers. The latter give rise to the sympathetic preganglionic fibers that form the white rami communicantes.

White rami communicantes do not reach the cervical, lower lumbar, sacral, and coccygeal ganglia of the sympathetic trunk. Essentially, they are the only pathway for preganglionic fibers from the CNS to the autonomic ganglia, as well as the main pathway for efferent connections of internal organs and blood vessels from the CNS. Topographically, the sympathetic trunk is divided into four parts: cervical, thoracic, lumbar, and sacral.

The cervical part of the sympathetic trunk extends from the level of the skull base to the thoracic inlet. It includes three ganglia: superior, middle, and inferior, which are connected by interganglionic branches. The largest ganglion of the sympathetic trunk is the superior cervical ganglion. Most commonly, this ganglion is located at the level of the first three cervical vertebrae. Branches arising from the superior cervical ganglion provide sympathetic innervation to the organs, skin, and Blood vessels of the HEAD and Neck.

Along the course of the blood vessels (the external and internal carotid and vertebral Arteries), these branches form plexuses that innervate the lacrimal and Salivary Glands, the Glands of the mucous membrane of the Pharynx, Larynx, and other organs, and participate in The formation of the cardiac plexus.

The middle cervical ganglion is inconstant; it lies at the level of the IV—VII cervical vertebrae and gives off branches for the Innervation of the Heart, neck vessels, and the thyroid and Parathyroid glands.

The cervicothoracic (stellate) ganglion lies at the level of the neck of the I rib, posterior to the Subclavian Artery. It gives off branches to innervate The Thyroid Gland, Vessels of the Brain AND SPINAL cord, and mediastinal organs, forms the deep and superficial cardiac and other plexuses, and provides sympathetic innervation to The Heart.

The thoracic part of the sympathetic trunk consists of 10—12 thoracic ganglia of fusiform or triangular shape, which lie anterior to the heads of the Ribs on the lateral surface of the vertebral bodies. Branches arise from this part to participate in the Formation of the cardiac, pulmonary, esophageal, thoracic, aortic, and other plexuses, innervating the corresponding organs. The thoracic part gives rise to its largest branches: the greater and lesser splanchnic nerves, which enter the Abdominal cavity between the crura of the Diaphragm, reach the celiac plexus, and terminate there.

The lumbar part is formed by 2—7 lumbar ganglia and contains two groups of branches: gray rami communicantes and lumbar splanchnic nerves. The gray rami communicantes run to all lumbar spinal nerves. The lumbar splanchnic nerves connect the lumbar part of the sympathetic trunk with the prevertebral plexuses of the abdominal cavity, the vascular nerve plexuses of the lumbar arteries and other vessels, and the abdominal organs, providing their sympathetic innervation.

The sacral part of the sympathetic trunk consists of four sacral ganglia, each about 5 mm in size, connected by interganglionic branches. The ganglia lie on the pelvic surface of the sacrum, medially to the pelvic sacral foramina. The branches of these ganglia participate in the formation of the pelvic plexuses, which innervate the glands, blood vessels, and Organs of the pelvic region (terminal PARTS OF THE intestine, urogenital organs of the lesser pelvis, and external genitalia).

In the abdominal and pelvic cavities, there are autonomic nerve plexuses of various sizes, consisting of autonomic ganglia and interconnecting bundles of nerve fibers. Topographically, the following main plexuses are distinguished in the abdominal cavity: the celiac, superior and inferior mesenteric, abdominal aortic, intermesenteric, superior and inferior hypogastric plexuses, hypogastric nerves, and others.

The celiac plexus is located at the level of the XII thoracic vertebra and is horseshoe-shaped, surrounding the arterial trunk of the same name. It is the largest of all prevertebral plexuses in the abdominal cavity.

The celiac plexus consists of several large ganglia and numerous nerves connecting them. The right and left greater and lesser splanchnic nerves from the thoracic ganglia, and the lumbar splanchnic nerves from the lumbar ganglia of the sympathetic trunk, approach the celiac plexus. Fibers of the Vagus nerve and sensory fibers of the right phrenic nerve also join the celiac plexus. Afferent, pre-, and postganglionic sympathetic fibers reach the celiac plexus within the splanchnic nerves and visceral branches from the lumbar sympathetic ganglia. Nerve branches arise from the celiac ganglia to form plexuses of the same name around the celiac trunk and its branches; these plexuses travel along with the arteries to the corresponding organs to provide their innervation (hepatic, splenic, gastric, pancreatic, suprarenal, and phrenic plexuses). The superior mesenteric plexus is closely associated with the celiac plexus and innervates the abdominal organs supplied by the superior mesenteric artery.

The abdominal aortic plexus is a direct continuation of the celiac and superior mesenteric plexuses and is one of the largest Autonomic plexuses lying on the aorta. From this plexus, fibers travel along the Branches of the inferior mesenteric artery to reach and innervate the organs supplied by this artery. Further down, the abdominal aortic plexus continues onto the common iliac arteries as the right and left iliac plexuses. The abdominal aortic plexus then transitions into the unpaired superior hypogastric plexus, located on the front surface of the aorta and the bodies of the lower lumbar vertebrae. Slightly below the sacral promontory, the superior hypogastric plexus divides into two nerve bundles—the right and left hypogastric nerves, which transition into the right and left inferior hypogastric (pelvic) plexuses, respectively. This is one of the largest autonomic plexuses; through its branches, it participates in the Formation of secondary visceral plexuses (rectal, prostatic, and deferential plexuses in men, and the uterovaginal plexus in women) and provides sympathetic innervation to the pelvic organs.