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Flashcards in Enteric Nervous System Deck (23)
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What is the general function of the parasympathetic NS in the enteric system?

STIMULATES motility in GI tract
project from the medulla oblongata and sacral regions of the spinal cord


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

1. SLOWS DOWN motility
2. High sympathetic activity during fight or flight


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

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


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

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


What is the main neurotransmitter of excitatory muscle motor neurons?



What is the main neurotransmitter of inhibitory muscle motor neurons?

Nitric oxide, VIP (vasoactive intestinal peptide)


Describe how neurons contribute to the peristalsis process

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


Describe sensory activity in the intestinal wall

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


What is the function of secretomotor and vasomotor neurons?

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


What are the 4 parts of the enteric NS?

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


Describe Hirschsprung’s disease

1. No sacral root innervation of descending colon
2. Cannot have bowel mvt because there is no smooth contraction process


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

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


Describe Achalasia

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


Describe congenital hypertrophic pyloric stenosis

Cannot relax pyloric sphincter (right before anus)


what is "law of the intestine"

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


describe ENS

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


anatomy of ENS

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


function of sensory neurons

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


function of serotonin

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


function of ICC

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


origin of ENS

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


how to study ENS in culture dish

slide 26 and 27


migration of ENS crest cells

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