TBL17 - Enteric Nervous System

Question 1

What two plexuses does the enteric nervous system (ENS) consist of? How far does the ENS extend along the GI tract?

Answer 1

1) The enteric nervous system (ENS) consists of a myenteric plexus between the two layers of the muscularis externa and a submucosal plexus between the mucosa and muscularis externa
2) The ENS extends along the entire GI tract

Question 2

What do the ENS plexuses contain and where do they derive from?

Answer 2

The ENS plexuses contain visceral (parasympathetic) motor and sensory neurons, which like neurons of the sympathetic ganglia and DRG, are derivatives of neural crest cells

Question 3

What activates sensory neurons of the ENS? What do these neurons do once activated?

Answer 3

Local mechanical or chemical stimuli activate sensory neurons of the ENS, which synaptically activate parasympathetic neurons of the myenteric plexus to induce serial contractions of the muscularis externa that create peristaltic waves along the GI tract

Question 4

What does activation of parasympathetic neurons in the submucosal plexus stimulate?

Answer 4

Similar activation of parasympathetic neurons in the submucosal plexus stimulates secretion by glandular epithelial cells (e.g., chief and mucous cells) and activates entero-endocrine cells, which are diffusely scattered in the epithelium and produce ≥ 30 hormones

Question 5

What forms the periarterial plexuses that supply the foregut-derived GI tract? How do sympathetic and parasympathetic fibers control the physiologic digestive process?

Answer 5

1) Postsynaptic sympathetic fibers and branches of the vagus nerves form periarterial plexuses to supply the foregut-derived GI tract
2) By synapsing with neurons of the ENS, the sympathetic and parasympathetic fibers inhibit and accelerate the physiologic digestive processes, respectively