ANS Abdomen

Question 1

How is the adrenal medulla a primary contributor to stress syndrome?

Answer 1

Release of norepinephrine and epinephrine by Chromaffin cells in the adrenal medulla augment the local SANS innervation

Question 2

What is the course of upper GI PANS? (i.e. stomach, duodenum, liver, spleen, pancreas)

Answer 2

Preganglionic nucleus: Dorsal motor nucleus of X
Preganglionic axon: follow right and left vagus nerves to esophageal plexus, enter abdomen via anterior and posterior vagal trunks, pass through celiac plexus, follow blood vessels to visceral wall of target
Synapse: Terminal ganglia
Postganglionic axon: innervates smooth muscle and glands in GI wall or in smooth muscle in blood vessels

Question 3

What is the PANS function of upper GI?

Answer 3

Enhances peristalsis, relaxes pyloric sphincter, increases GI secretions (enzymatic + mucous), vasodilated for greater mobilization of absorbed foods into portal circulation.

Question 4

What is the PANS innervation of lower GI? Including jejunum, ileum, cecum, ascending, transverse, descending, sigmoid colons, and rectum.

Answer 4

Vagus nerve: all elements before left colic flexure, via lower abdominal (inferior mesenteric) plexus

Pelvic splanchnic nerves from S2-S4: all elements after colic flexure (descending + sigmoid colon, rectum)

Question 5

What is the course of the SANS innervation of the upper abdominal plexus?

Answer 5

Nucleus: intermediolateral cell column T5-T12
Preganglionic fibers: Emerge as WCR through sympathetic chain ganglion as greater (G), lesser (L), and least (l) thoracic splanchnic nerves
Synapse: Collateral ganglia (celiac, superior mesenteric, aorticorenal)
Postganglionic fibers: follow branches of superior mesenteric and nearby arteries to targets

Question 6

What vertebral levels to greater, lesser, and least splanchnic nerves correspond to?

Answer 6

G - T5-T9 - To celiac ganglion
L - T10-T11
l - T12

Question 7

What is the course of the SANS innervation of the lower abdominal plexus?

Answer 7

Nucleus: intermediolateral cell column L1-L2
Preganglionic fibers: Emerge as WCR through lumbar ganglia LG1-LG3 of sympathetic chain ganglion as 3-4 lumbar splanchnic nerves
Synapse: Collateral ganglia (inferior mesenteric, or scattered ganglia in pelvic plexus)
Postganglionic fibers: follow branches of inferior mesenteric and nearby arteries to targets

Question 8

What are the upper and lower abdominal collateral ganglia?

Answer 8

Upper: Celiac, superior mesenteric, aorticorenal
Lower: Inferior mesenteric, pelvic plexus ganglia

Question 9

What is the SANS function to the abdominal viscera and via what receptors?

Answer 9

Beta-2 adrenergic - decreases GI motility (peristalsis) and glandular secretion, as in lungs
Alpha adrenergic - causes vasoconstriction to redirect blood from viscera to skeletal muscle during stress syndrome

Question 10

What makes up the upper abdominal / celiac plexus?

Answer 10

1. PANS preganglionic fibers from vagus nerve
2. Preganglionic SANS from thoracic splanchnic nerves, collateral ganglia (celiac, sup. mesenteric, aorticorenal), postganglionic SANS
3. Visceral afferent fibers following sympathetics

Question 11

What are subsidiary plexuses? What are some upper and lower examples?

Answer 11

Continuations of the abdominal plexuses as it extends over vessels to their targets. Mostly branches of abdominal aorta.
Upper: Hepatic, gastric, renal
Lower: Inferior mesenteric, gonadal

Question 12

What makes up the lower abdominal / inferior mesenteric plexus?

Answer 12

1. 2-3 Lumbar splanchnic nerves + inferior mesenteric ganglion, postganglionic sans
2. Contributions from upper abdominal plexus

Question 13

What are the two divisions of the enteric plexus? What is it?

Answer 13

1. Submucosal (Meissner’s)
2. Myenteric (Auerbach’s)

It is a complex network of ANS neurons and local neurons (both sensory + motor) which control the activities of GI

Question 14

Why is PANS needed for the enteric plexus?

Answer 14

Facilitates mobilization of absorbed foods during digestion

Question 15

What are the four local neural cell types of the enteric plexus?

Answer 15

1. Burst cell
2. Follower cell
3. Mechanoreceptor - responding to stretch
4. Inhibitory intrinsic

Question 16

What is the function of the burst neuron?

Answer 16

A leader cell which facilitates the follower neuron. It has pacemaker properties

Question 17

What is the function of the follower neuron?

Answer 17

It is facilitated by the burst neuron, and functions to hyperpolarize smooth muscle cells to prevent contraction in the absence of food

Question 18

What is the function of the mechanoreceptor cell?

Answer 18

Senses distention of the GI wall when food comes. If GI is distended, it activates the inhibitory intrinsic neuron

Question 19

What is the function of the inhibitory intrinsic neuron?

Answer 19

When activated by the mechanoreceptor cell in response to food, it inhibits the action of the follower neuron. Thus, the smooth muscle cells can depolarize and ultimately contract.

Question 20

What is meant by disinhibition of smooth muscle cells?

Answer 20

When the follower neuron is deactivated by the inhibitory intrinsic neuron, the smooth muscle cell becomes disinhibited by the impulses of inhibition propagated by the burst neuron + follower neuron system

Question 21

What happens after smooth muscle cells contract locally?

Answer 21

The signal spreads to other smooth muscle cells via their gap junctions, thus initiating the wave-like contraction of peristalsis, from proximal to distal

Question 22

What is Hirschsprung’s disease? What are the symptoms?

Answer 22

“Colonic aganglionosis”

Failure of neural crest to make terminal ganglia of enteric plexus, especially in lower colon. Causes chronic constripation, obstruction, and megacolon (constriction of a distal section due to no PANS leads proximal section to become dilated with feces)

Question 23

What is Crohn’s disease?

Answer 23

Multifactorial inflammatory disorder characterized by GI inflammation with bacteria accumulation in the GI mucosa from mouth to anus, most prevalent in ileum.

• 15-30 years of age onset
• Flare-ups followed by remissions of abdominal pain, and frequent diarrhea

Question 24

Where does stomach referred pain follow? (i.e. carcinoma of stomach)

Answer 24

Left greater splanchnic nerve (T5-T9)

Pain over left epigastrium

Question 25

Where does gall bladder referred pain follow? (i.e. gallstones). How about if it is severe?

Answer 25

Right greater splanchnic nerve (T5-T9)

If spreads to lower surface of diaphragm:
Right phrenic nerve (C3-C5)

Leads to pain over right shoulder as well as right epigastrium

Question 26

Where does appendicitis pain refer to in early and late stages?

Answer 26

Early: Lesser splanchnic nerve (T10-T11)
Pain in umbilical region
Later: Right lumbar splanchnic nerves (L1-L2)
Pain in right lower quadrant

Question 27

Where does kidney referred pain follow? (i.e. kidney stones)

Answer 27

Follows right or left least splanchnic nerve (T12).

Pain in lower quadrant (subcostal, T12)