The duodenum is innervated by the parasympathetic and sympathetic parts of the autonomic nervous system. The nerve fibers of both systems extend throughout the entire length of the small intestine and synapse with the neurons located in the intestinal wall, forming two plexuses:

Submucosal plexus (Meissner’s plexus) - located in the submucosal layer; contains only the parasympathetic fibers;
Myenteric plexus (Auerbach’s plexus) - positioned in the muscularis externa between both its layers; contains parasympathetic and sympathetic nerve fibers.

Parasympathetic innervation

The duodenum receives parasympathetic innervation from the fibers of the vagus nerve (CN X) via the anterior and posterior vagal trunks. The anterior vagal trunk contains mostly fibers of the left vagus nerve, while the posterior vagal trunk is composed of fibers of the right vagus nerve.

The parasympathetic fibers stimulate intestinal gland secretion and smooth muscle cell contractions. Also, they provide widening (vasodilation) of the lumen of the intestinal blood vessels.

Sympathetic innervation

The sympathetic innervation of the duodenum occurs via the greater thoracic splanchnic nerves that participate in the formation of the superior mesenteric plexus around the superior mesenteric artery and celiac plexus around the celiac trunk. The sympathetic fibers ensure narrowing (vasoconstriction) of the lumen of the intestinal vessels, relaxation of smooth muscle cells and inhibition of intestinal gland secretion.

The bodies of the preganglionic sympathetic neurons are located in the gray matter of the fifth to ninth thoracic segments (T5 - T9) of the spinal cord. Axons of these neurons form the greater and lesser thoracic splanchnic nerves that travel to the celiac and superior mesenteric plexuses and synapse there with the neurons of the celiac and superior mesenteric ganglia. Postganglionic axons then travel to the duodenum via the periarterial branches and supply it.

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Innervation of duodenum