The muscularis propria of the intestine is the functional motor apparatus of the gut, consisting of inner circular and outer longitudinal smooth muscle layers controlled by the myenteric plexus. Peristalsis is an intrinsic property of the enteric nervous system, persisting even after all extrinsic nerve connections are severed. The taeniae coli of the large bowel represent condensed longitudinal muscle segments.
| Origin | Throughout the small and large intestine: an inner circular layer and an outer longitudinal layer of smooth muscle, with the myenteric (Auerbach's) plexus located between them; the longitudinal layer of the colon is condensed into three taeniae coli |
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| Insertion | Continuous throughout the bowel wall; no discrete origin or insertion; the smooth muscle cells are interconnected by gap junctions allowing coordinated peristalsis |
| Nerve Supply | Enteric nervous system (Auerbach's myenteric plexus between the two muscle layers — primary control); Vagal parasympathetic — promotes motility; Sympathetic via coeliac and mesenteric plexuses — inhibits motility; 5-HT (serotonin) from enterochromaffin cells — key mediator |
| Blood Supply | Superior and inferior mesenteric arteries and their branches |
| Actions | Circular muscle contraction narrows the bowel lumen and propels contents forward (peristalsis); longitudinal muscle contraction shortens the bowel; coordinated peristaltic waves propel intraluminal contents from stomach to anus; segmentation contractions in the small bowel mix contents without net propulsion |
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Post-operative ileus involves temporary muscularis propria dysfunction from surgical handling, anaesthetic agents, and opioids, producing absent peristalsis and bowel distension. Chronic intestinal pseudo-obstruction (Ogilvie syndrome) involves colonic muscularis propria dysfunction without mechanical obstruction. Hirschsprung disease involves absence of myenteric plexus ganglia, producing tonic smooth muscle contraction of the aganglionic segment. Irritable bowel syndrome involves abnormal muscularis propria motility patterns producing alternating constipation and diarrhoea.
Bowel handling, anaesthetic agents, opioids, and electrolyte disturbances inhibit the muscularis propria myenteric reflex arc, producing post-operative ileus with absent bowel sounds, distension, and failure to pass flatus; management includes early mobilisation, minimising opioids, prokinetics (neostigmine for colonic ileus), and nasogastric decompression if vomiting persists beyond 3-4 days.
