Greater thoracic splanchnic nerve

Greater thoracic splanchnic nerve is a visceral sympathetic nerve which arises from the 5th to 9th thoracic ganglia of the thoracic sympathetic chain, on either side. There is a potential for contribution from the 10th thoracic ganglia as well. The nerve descends ventrally and medially as it traverses the aortic hiatus of the diaphragm to terminate at the pre-aortic ganglion (a.k.a. coeliac ganglion) within the coeliac prevertebral plexus.

Like most other splanchnic nerves, the greater thoracic splanchnic nerve contains pre-ganglionic sympathetic neurons, which arise from the lateral horns of spinal cord and traverse un-relayed through the sympathetic trunk. They synapse with cell bodies of post-ganglionic sympathetic neurons within the coeliac ganglion, on either side. The coeliac ganglia, as you may know, are situated within the coeliac neuronal plexus that spans around the coeliac and superior mesenteric arteries. From here onwards, the post-ganglionic sympathetic neurons follow the coeliac plexus as it invests the arterial branches of the coeliac trunk to reach various visceral organs in the abdomen.

The greater thoracic splanchnic nerve inhibits the motility and secretions of the foregut. The sympathetic innervation stimulates gluconeogenesis. It promotes the release of glucose by glycogenolysis, while increasing glucagon and decreasing insulin secretion. Further actions include contraction of gall bladder, secretion of pancreatic enzymes, release of catecholamines from the chromaffin cells and transmission of pain signals via the visceral afferent neurons.