Thoracic Sympathetic Chain and Splanchnic Nerves


Each ganglion receives at least one white ramus communicans and contributes at least one gray ramus to the adjacent spinal nerve, although several white and gray rami communicantes may be attached to each ganglion. Visceral branches are supplied to the heart and pericardium, lungs, trachea and bronchi, esophagus, and thymus.


Sympathetic Cardiac Nerves. Three pairs of sympathetic cardiac nerves arise from the cervical trunk ganglia, and the others emerge from the upper thoracic ganglia.


The superior cervical sympathetic cardiac nerves originate from the corresponding trunk ganglia. On the right, the nerve passes posterolateral to the brachiocephalic artery and aortic arch; on the left, it curves downward over the left side of the aortic arch to reach the cardiac plexus.


The middle cervical sympathetic cardiac nerves are usually larger than the corresponding superior and inferior nerves. They arise from the middle cervical and vertebral ganglia of the sympathetic trunks and usually run independently to the cardiac plexus.


The inferior cervical sympathetic cardiac nerves consist of fibers arising from the cervicothoracic ganglia and subclavian ansae.


The thoracic sympathetic cardiac nerves are four or five slender branches, which run forward and medially from the thoracic trunk ganglia to the cardiac plexus.


Parasympathetic Cardiac Nerves. Three pairs of parasympathetic (vagal) cardiac nerves are usually present. The superior cervical vagal cardiac branches leave the vagus nerves in the upper part of the neck. The inferior cervical vagal cardiac branches arise in the lower third of the neck and descend posterolateral to the brachiocephalic artery and aortic arch on the right side; on the left side, they descend lateral to the left common carotid artery and aortic arch. The thoracic vagal cardiac branches arise at or below the level of the thoracic inlet.


Multiple interconnections exist between all the sympathetic and parasympathetic cardiac nerves and between the cardiac and other visceral branches of the sympathetic trunks.


Other thoracic sympathetic branches supply the thoracic viscera from the paired greater, lesser, and lowest thoracic splanchnic nerves, although these are mainly destined to supply abdominal structures and contain a mixture of preganglionic, postganglionic, and afferent fibers. The greater (major) splanchnic nerve lies medial to the ipsilateral sympathetic trunk and enters the abdomen by piercing the crus of the diaphragm. The lesser (minor) splanchnic nerve lies slightly lateral to the greater splanchnic nerve and also usually pierces the diaphragmatic crus. The lowest (imus) splanchnic nerve is inconstant.


Minute twigs from the sympathetic trunks join and innervate the intercostal arteries. Other sympathetic postganglionic fibers reach these vessels in fascicles from adjacent intercostal nerves or their branches, and these also carry sudomotor and pilomotor fibers.


The muscular, osseous, and articular fibers from the thoracic sympathetic trunks and their branches supply the adjacent structures concerned; their exact functions are uncertain.


INNERVATION OF HEART


The heart is supplied by sympathetic nerves arising mainly in the neck because the heart develops initially in the cervical region and later migrates into the thorax, taking its nerves down with it. The parasympathetic supply is conveyed in cardiac branches of the vagus nerves.


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Sep 2, 2016 | Posted by in NEUROLOGY | Comments Off on Thoracic Sympathetic Chain and Splanchnic Nerves

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