GI Anatomy

Question 1

Sympathetic innervation causes vasoconstriction and inhibition of peristalsis. Where do the presynaptic (preganglionic) fibers originate from?

Answer 1

IML of T5-L2. Fibers travel to sympathetic ganglia WITHOUT synapsing and then go to the splanchnic nerves.

Question 2

For structures proximal to the left colic flexure, which splanchnic nerves are used for sympathetic innervation?

Answer 2

Greater, Lesser or Least

Question 3

For structures distal to the left colic flexures, which splanchnic nerves are used for sympathetic innervation?

Answer 3

Lumbar

Question 4

Parasympathetic innervation causes vasodilation and promotes peristalsis. What nerve are the presynaptic fibers associated with proximal to the L colic flexure? Distal to the L colic flexure?

Answer 4

Vagus nerve (CN X) is associated with presynaptic fibers proximal to the L colic flexure. The S2-S4 spinal cord gives off presynaptic fibers and follow pelvic splanchnic nerves to innervate distal to the L colic flexure.

Question 5

Where do presynaptic parasympathetic fibers synapse?

Answer 5

On enteric parasympathetic ganglia within walls of target organ.