Expansion
Intrinsic enteric plexuses modulated by parasympathetic and sympathetic input
Expansion
Intrinsic (enteric nervous system)
- Myenteric (Auerbach) plexus: between the muscle layers, controlling motility
- Submucosal (Meissner) plexus: controlling secretion and blood flow
- Contains more neurones than the spinal cord, and can operate autonomously
Extrinsic
- Parasympathetic (vagus above, and pelvic splanchnics for the distal colon): generally stimulatory to motility and secretion
- Sympathetic (from the coeliac, superior and inferior mesenteric ganglia): generally inhibitory, and vasoconstrictor
Pacemakers: the interstitial cells of Cajal generate slow waves setting the basic electrical rhythm, about 3 per minute in the stomach and 12 per minute in the duodenum. Contraction occurs only when spike potentials are superimposed on a slow wave.
Reflexes worth knowing: the gastrocolic reflex (eating stimulates colonic mass movement), the enterogastric reflex (duodenal contents slow gastric emptying), and the intestino-intestinal reflex (distension in one segment inhibits the rest, part of the mechanism of paralytic ileus).