The nerves of the small intestines are derived from the plexuses of parasympathetic nerves around the superior mesenteric artery. From this source, they run to the myenteric plexus (Auerbach's plexus) of nerves and ganglia situated between the circular muscular fibers and the longitudinal muscle fibers of the muscularis externa. From this a secondary plexus, the plexus of the submucosa (Meissner's plexus, submucous plexus, submucosal plexus, plexus submucosus) is derived, and it is formed by branches that have perforated the circular muscular fibers. This plexus lies in the submucous coat of the intestine; it also contains ganglia from which nerve fibers pass to the muscularis mucosae and to the mucous membrane.
The nerve bundles of the submucous plexus are finer than those of the myenteric plexus. Its function is to innervate cells in the epithelial layer and the smooth muscle of the muscularis mucosae.