GI Neural Control

Question 1

What are the two plexuses of the enteric nervous system?

Answer 1

Myenteric  (Auerbach's plexus)- outer plexus between longitudinal and circular muscle layer. CONTROLS GI MOVEMENT
Submucosal plexus (Meissner's plexus)- inner plexus in submucosa. CONTROLS GI SECRETION & BLOOD FLOW

Question 2

What are the 12 types of neurotransmitters identified that are released by nerve endings of enteric neurons

Answer 2

Acetylcholine, norepi, ATP, serotonin, dopamine, CCK, substance P, vasoactive intestinal polypeptide, somatostatic, bombesin, leu-enkephalin, met-enkaphalin.

Question 3

What effect does Ach have on the GI system?

Answer 3

Most often excites

Question 4

What effect do Norepi (and Epi) have on GI activity?

Answer 4

Almost always inhibits GI activity

Question 5

What effect does parasympathetic stimulation have on the enteric system?

Answer 5

Increases activity

Question 6

What effect does sympathetic stimulation have on GI activity?

Answer 6

Inhibits activity. By direct effect of of secreted norepi to inhibit smooth muscle, and moreso by inhibitory effect of norepi on neurons of the entire enteric nervous system.

Question 7

80% of nerve fibers in vagus nerves are afferent or efferent?

Answer 7

Afferent. They transmit sensory signals from the GI tract into the brain medulla, initiating vagal reflex signals that return to the GI tract to control its functions.

Question 8

What are the 3 GI reflexes essential to GI control?

Answer 8

Reflexes integrated entirely in gut wall- control secretion, peristalsis, mixing, inhibitory effects

From gut to prevertebral sympathetic ganglia and back- transmit signals long distances. Gastrocolic reflex, enterogastric relfex, colonoileal reflex.

From gut to spinal cord/brain stem and back. vagus nerve to control gastric motor and sensory, pain reflexes that inhibit GI tract, and defecation reflexes that travel from colon and rectum to cord and back to produce defecation.