Neural Control The small intestine and colon have intrinsic and extrinsic innervation. The intrinsic innervation, also called the enteric nervous system, comprises myenteric, submucosal, and mucosal neuronal layers. The function of these layers is modulated by interneurons through the actions of neurotransmitter amines or peptides, including acetylcholine, vasoactive intestinal peptide (VIP), opioids, norepinephrine, serotonin, ATP, and nitric oxide. The myenteric plexus regulates smooth-muscle function, and the submucosal plexus affects secretion, absorption, and mucosal blood flow. The extrinsic innervations of the small intestine and colon are part of the autonomic nervous system and also modulate motor and secretory functions. The parasympathetic. | Chapter 040. Diarrhea and Constipation Part 2 Neural Control The small intestine and colon have intrinsic and extrinsic innervation. The intrinsic innervation also called the enteric nervous system comprises myenteric submucosal and mucosal neuronal layers. The function of these layers is modulated by interneurons through the actions of neurotransmitter amines or peptides including acetylcholine vasoactive intestinal peptide VIP opioids norepinephrine serotonin ATP and nitric oxide. The myenteric plexus regulates smooth-muscle function and the submucosal plexus affects secretion absorption and mucosal blood flow. The extrinsic innervations of the small intestine and colon are part of the autonomic nervous system and also modulate motor and secretory functions. The parasympathetic nerves convey visceral sensory and excitatory pathways to the colon. Parasympathetic fibers via the vagus nerve reach the small intestine and proximal colon along the branches of the superior mesenteric artery. The distal colon is supplied by sacral parasympathetic nerves S2-4 via the pelvic plexus these fibers course through the wall of the colon as ascending intracolonic fibers as far as and in some instances including the proximal colon. The chief excitatory neurotransmitters controlling motor function are acetylcholine and the tachykinins such as substance P. The sympathetic nerve supply modulates motor functions and reaches the small intestine and colon alongside their arterial vessels. Sympathetic input to the gut is generally excitatory to sphincters and inhibitory to nonsphincteric muscle. Visceral afferents convey sensation from the gut to the central nervous system initially they course along sympathetic fibers but as they approach the spinal cord they separate have cell bodies in the dorsal root ganglion and enter the dorsal horn of the spinal cord. Afferent signals are conveyed to the brain along the lateral spinothalamic tract and the nociceptive dorsal column pathway and are
