The enteric nervous system, slow waves and GI control !

Regulation
Exam priority: medium

The gut has its own network of neurons: it sets the rhythm, mixes and pushes contents; the vagus and sympathetic nerves only adjust the volume.

Updated 2026-11-01

Also called: Myenteric plexus, Interstitial cells of Cajal

See it in 3D: Stomach · Vagus nerve · Vagal trunks · Mesenteric and aortic plexuses · Celiac plexus · Splanchnic nerves · Sympathetic trunk

Key points

Myenteric plexus (between longitudinal and circular layers): motility. Submucosal plexus: secretion, absorption and blood flow.
Slow waves (Cajal cells) do not cause contraction on their own; contraction happens when spike potentials, carried by Ca²⁺ entry, ride on top of them.
Slow-wave frequency: stomach ≈3/min, duodenum ≈12/min, ileum ≈8–9/min.
Parasympathetic (vagus to the proximal transverse colon; pelvic splanchnic nerves S2–S4 for the distal colon): generally stimulates. Sympathetic (T5–L2): inhibits motility and contracts sphincters.
Peristaltic reflex: contraction above the bolus (acetylcholine, substance P) and relaxation below it (VIP, nitric oxide).
Loss of inhibitory neurons: achalasia (including the Chagas form, relevant in Colombia); congenital absence of ganglia in the distal colon: Hirschsprung disease.

What it is

The enteric nervous system is a network of hundreds of millions of neurons in the wall of the gut that can work even when cut off from the brain. The myenteric (Auerbach) plexus mainly controls motility and the submucosal (Meissner) plexus controls secretion and local blood flow. Interstitial cells of Cajal generate slow waves that set the maximum contraction rate of each segment.

Key facts

Excitatory transmitters: acetylcholine and substance P. Inhibitory: VIP and nitric oxide (also ATP).
Long reflexes (vagovagal, through the brainstem) and short reflexes (within the wall) combine with prevertebral reflexes (through sympathetic ganglia).
Classic reflexes: gastrocolic (a full stomach activates the colon), enterogastric (the duodenum brakes the stomach), gastroileal (food opens the ileocecal valve).
Between meals, the migrating motor complex sweeps the stomach and small bowel every ≈90–120 min, coordinated by motilin.
Resting potential of GI smooth muscle oscillates around ≈−50 to −60 mV; stretch, acetylcholine and parasympathetic input depolarize it.

Regulation

+Parasympathetic (vagus, pelvic nerves): Increases motility and secretion; relaxes some sphincters through inhibitory neurons
−Sympathetic (noradrenaline): Slows motility, contracts sphincters and reduces splanchnic blood flow
+Stretch of the wall: Depolarizes muscle and triggers the peristaltic reflex
−Opioids (μ receptors): Inhibit acetylcholine release: less propulsion and constipation

Clinical notes

Postoperative ileus: handling of the bowel and raised sympathetic tone paralyse the gut for a while.
Diabetic autonomic neuropathy: gastroparesis, nocturnal diarrhea or constipation.
Chagas disease destroys myenteric neurons and can cause megaesophagus and megacolon.
Irritable bowel syndrome: a disturbed gut–brain axis with visceral hypersensitivity and no structural lesion.

Test yourself

Think of the answer, then tap the question to see it.

Why does a slow wave on its own not make intestinal smooth muscle contract?

The slow wave only oscillates the membrane potential. Contraction needs depolarization past threshold that fires spike potentials with Ca²⁺ entry.

Which transmitters relax the segment below a bolus during peristalsis?

VIP and nitric oxide released by inhibitory myenteric neurons; above the bolus, acetylcholine and substance P cause contraction.

Why does Hirschsprung disease cause functional obstruction of the distal colon?

Ganglion cells, including inhibitory neurons, are missing; that segment stays tonically contracted and cannot relax to let contents pass.

What is the slow-wave frequency in the stomach, duodenum and ileum, and what does it set?

≈3/min in the stomach, ≈12/min in the duodenum and ≈8–9/min in the ileum. It sets the maximum rate at which that segment can contract.

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See it in 3D

The structures of Durgical's 3D anatomy where it happens.

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Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: 23.2 Digestive System Processes and Regulation (OpenStax (Rice University), 2022); Achalasia (StatPearls (NCBI Bookshelf), 2024); Irritable Bowel Syndrome (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 63). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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