Introduction to GI physiology

Lies in the wall of the gut, beginning in the esophagus and extending all the way to the anus.

no of neurons in this enteric system is almost exactly equal to the no in the entire spinal cord (100 million)

The enteric nervous system is composed mainly of two plexuses

myenteric plexus or Auerbach’s plexus, and the submucosal plexus or Meissner’s plexus, that lies in the submucosa.

Myenteric plexus

consists mostly of a linear chain of many interconnecting neurons.

is concerned mainly with controlling muscle activity along the length of the gut

Stimulation of the plexus causes

↑ed tonic contraction, or “tone,” of the gut wall,

↑ed intensity of the rhythmical contractions,

slightly ↑ed rate of the rhythm of contraction, and 

↑ed velocity of conduction of excitatory waves along the gut wall, causing more rapid movement of the gut peristaltic waves.

Submucous

the submucous plexus innervates the glandular epithelium, intestinal endocrine cells, and submucosal blood vessels.

primarily involved in the control of intestinal secretion

neurotransmitters: acetylcholine, the amines norepinephrine and serotonin, the amino acid GABA, the purine ATP, the gases NO and CO, and many different peptides and polypeptides.

The parasympathetic supply to the gut is divided into cranial and sacral divisions

cranial fibers provide extensive innervation to the esophagus, stomach, and pancreas and somewhat less to the intestines

Sacral division innervates the distal half of the large intestine and all the way to the anus.

parasympathetic cholinergic activity generally increases the activity of intestinal smooth muscle