Enteric Nervous System

Question 1

What is the general function of the parasympathetic NS in the enteric system?

Answer 1

STIMULATES motility in GI tract

project from the medulla oblongata and sacral regions of the spinal cord

Question 2

What is the general function of the sympathetic NS in the enteric system? (not in the lecture)

Answer 2

1. SLOWS DOWN motility

2. High sympathetic activity during fight or flight

Question 3

What are the muscles in the intestinal wall? How are they oriented and where are they located?

Answer 3

1. Longitudinal muscle – travels along the intestine. Outer.
2. Circular muscle – travels around the intestine. Inner.

Question 4

What is the arrangement of ganglia and muscles (inner – outer) in the intestinal wall?

Answer 4

(Inner) submucosal ganglia > circular muscle > myenteric ganglia > longitudinal muscle

Question 5

What is the main neurotransmitter of excitatory muscle motor neurons?

Answer 5

Ach

5-HT

Question 6

What is the main neurotransmitter of inhibitory muscle motor neurons?

Answer 6

Nitric oxide, VIP (vasoactive intestinal peptide)

Question 7

Describe how neurons contribute to the peristalsis process

Answer 7

1. Food distends colon section
2. Proximal part of colon receives ascending interneuron which synapses on an excitatory motor neuron, causing contraction of the proximal intestine
3. Distal part of colon receives descending interneuron which synapses on an inhibitory motor neuron, causing relaxation of the distal intestine

Question 8

Describe sensory activity in the intestinal wall

Answer 8

Stretch receptors respond tonically (always fire) to stretch and phasically (fire in bursts) when the muscle is distended.

Question 9

What is the function of secretomotor and vasomotor neurons?

Answer 9

Control the balance between absorption and secretion of water and electrolytes

via sympathetic pathways

Cholinergic transmission is important

innervate the arterioles, help to balance secretion and vasodilation

Local computation of the need for vasodilation and local absorption to supply electrolyte for secretion determines the relative activation of vasodilator secretomotor neurons

Question 10

What are the 4 parts of the enteric NS?

Answer 10

1. Excitatory/inhibitory muscle motor neurons
2. Ascending/descending Interneurons
3. Sensory neurons
4. Secretomotor and vasomotor neurons

Question 11

Describe Hirschsprung’s disease

Answer 11

1. No sacral root innervation of descending colon

2. Cannot have bowel mvt because there is no smooth contraction process

Question 12

Which genes affect neural crest cell migration of neurons into the gut?

Answer 12

1. Phox-2b
2. SOX-10
3. RET (distal only)

Question 13

Describe Achalasia

Answer 13

Loss of enteric inhibitory motorneurons in the lower esophageal sphincter (sphincter right before stomach) > food gets stuck in esophagus
Symptoms are dysphagia, vomiting

Question 14

Describe congenital hypertrophic pyloric stenosis

Answer 14

Cannot relax pyloric sphincter (right before anus)

Question 15

what is “law of the intestine”

Answer 15

application of pressure to the intestinal lumen of anesthetized dogs resulted in oral contraction and anal relaxation

Question 16

describe ENS

Answer 16

Part of the autonomic nervous system
Present in the gut, pancreas and gall bladder
Contains about 100 million neurons
Different from any other peripheral nervous system
Can function independent of CNS
All components of peristaltic reflex are present in the system
Supported by enteric glia

Question 17

anatomy of ENS

Answer 17

The Enteric Nervous System (ENS) is an integrated network of neurons and glia within the wall of the gut;

The myenteric plexus directly controls intestinal motility;

The submucosal plexus controls mucosal secretion and responds to sensory stimuli from the intestinal surface;

Myenteric plexus between the longitudinal and circular muscle layer and extends from esophagus to rectum;

Submucosal plexus is mainly in the small and large intestine

Question 18

function of sensory neurons

Answer 18

Mucosal chemosensors sense acid, alkali
Mucosal mechanoreceptors detect pressure, stroking, puff of air
Stretch responsive neurons respond tonically to stretch and phasically to distortion, continue to discharge when the muscle is stretched therefore distended muscle generates successive waves of peristaltic activity if distention is maintained

Question 19

function of serotonin

Answer 19

Stored in the enterochromoffin cells in sub cellular granules
Serotonin released in response to pressure, vagal stimulation, acid, acetylcholine, cholera toxin, cancer chemotherapy
Stimulatory to bowel

Question 20

function of ICC

Answer 20

ICC: interstitial cells of Cajal - modulate smooth muscle (depolarization and pacemaker in stomach, rhythmic contraction secretes fluids and move them down for normal activity) - cells between neuron and muscle

ICC located in the myenteric plexus generate slow wave activity
Closely parallels inhibitory innervation of the neurons regulating tone of intestine
Loss of ICC and inhibitory neurons in pylorus leads to infantile pyloric stenosis

Question 21

origin of ENS

Answer 21

Derived from the vagal and sacral neural crest cells;

vagal neural crest migrate from spinal cord to ENS and then migrate down, while sacral neural crest migrate up

Question 22

how to study ENS in culture dish

Answer 22

slide 26 and 27

Question 23

migration of ENS crest cells

Answer 23

Vagal neural crest cells descend proximo-distal until the anal verge
Influenced by netrins from the myentric plexus or submusosal plexus
Leave the gut to form pancreatic ganglia
Endothelins and receptors are necessary for normal ENS development