TBL19 - Intestinal Innervation

Question 1

Where do the greater splanchnic nerves (T5-T9) synapse in the abdomen? What do postsynaptic sympathetic fibers contribute to in the abdomen?

Answer 1

1) The greater splanchnic nerves (T5-T9) synapse in the celiac ganglion
2) Postsynaptic sympathetic fibers contribute to the periarterial plexuses on branches of the celiac trunk to the foregut-derived viscera

Question 2

Where do the lesser splanchnic nerves (T10-T11) synapse in the abdomen? What do branches of the SMA convey to the midgut derivatives?

Answer 2

1) The lesser splanchnic nerves (T10-T11) synapse in the superior mesenteric ganglion
2) Branches of the SMA convey plexuses of postsynaptic sympathetic and visceral sensory fibers to the midgut derivatives

Question 3

Where is visceral pain from the midgut derivatives referred to and what is it perceived as?

Answer 3

Visceral pain from the midgut derivatives is referred to the umbilical region of the anterior abdominal wall where it is perceived as dull, diffuse pain

Question 4

What do branches of the vagus nerve contribute to in the abdomen? What do vagal fibers join together? How are ENS-regulated GI tract peristalsis and glandular secretion accelerated and decelerated?

Answer 4

1) Branches of the vagus nerves contribute to the celiac trunk derived periarterial plexuses
2) Vagal fibers join the SMA plexuses to the midgut derivatives
3) ENS-regulated GI tract peristalsis and glandular secretion are accelerated and decelerated by the parasympathetic and sympathetic fibers, respectively

Question 5

Where do the least splanchnic nerves (T12) and lumbar splanchnic nerves (L1-L2) synapse? What do periarterial plexuses on branches of the inferior mesenteric artery convey?

Answer 5

1) The least splanchnic nerves (T12) and lumbar splanchnic nerves (L1-L2) synapse in the inferior mesenteric ganglion
2) Periarterial plexuses on branches of the IMA convey postsynaptic sympathetic fibers to the hindgut derivatives

Question 6

Where do proximal hindgut derivatives refer visceral pain to? How are they able to do this and what do these nerve fibers accompany?

Answer 6

1) Proximal hindgut derivatives (distal third of transverse colon, descending colon, and superior half of sigmoid colon) refer visceral pain to the hypogastric region
2) They do so via visceral sensory fibers from DRG at T12-L2, which accompany the postsynaptic sympathetic fibers from the inferior mesenteric ganglion

Question 7

Where do the pelvic splanchnic nerves arise from and what do they consist of? What do the vagus nerves provide to the midgut derivatives?

Answer 7

1) The pelvic splanchnic nerves, which arise from spinal cord segments S2 to S4, consist of presynaptic parasympathetic fibers that synapse with enteric ganglia in the hindgut-derived viscera
2) The vagus nerves provide parasympathetic innervation to the midgut derivatives

Question 8

What accompanies the pelvic splanchnic nerves from S2 to S4? Where is visceral pain from the inferior half of the sigmoid colon, rectum, and upper anal canal referred to?

Answer 8

1) Visceral afferent fibers from DRG at S2 to S4 accompany the pelvic splanchnic nerves
2) Visceral pain from the inferior half of the sigmoid colon, rectum, and upper anal canal is referred to the posterior thighs and perineum (to be studied later)

Question 9

How does referral of visceral pain differ after diverticulosis develops in the upper half or lower half of the sigmoid colon?

Answer 9

1) Superior half of the sigmoid colon refers pain to the hypogastric (pubic) region
2) Inferior half of the sigmoid colon refers pain to the posterior thighs and perineum