GI Tract

Question 1

only substantial group of neurons outside the CNS = ? how many neurons?

Answer 1

enteric nervous system: 200 - 600 million neurons, equivalent to # in spinal cord

Question 2

enteric NS: what kind of reflex activity? how many plexuses?

Answer 2

neuronal circuits have autonomous reflex activity. 2 ganglionated plexuses along the digestive tract

Question 3

name of the two plexi in ENS + what they do

Answer 3

myenteric auerbach’s plexus = peristaltic reflex. submucous meisner’s plexus = secretion of gastric juices

Question 4

spontaneous mvts of GIT triggered by? movements coordinated by? modulation?

Answer 4

triggered by interstitial cells of Cajal. movements are coordinated by the ENS networks. modulated by external neuronal and hormonal inputs.

Question 5

peristaltic reflex: what is the law of intestine?

Answer 5

relaxation below a bolus of food, contraction above

Question 6

mucosal stimulation/gut distension: causes what? which does what?

Answer 6

stimulates 5HT release from mucosal enterochromaffin cells. 5HT excites terminals of ACh/CGRP containing intrinsic primary afferent neurons

Question 7

intrinsic primary afferent neurons: release what? relay stimulus to what via what?

Answer 7

after being excited by 5HT, release CGRP or ACh. relay stimulus to ascending + descending motor neurons via one or more interneurons

Question 8

ascending vs. descending effects

Answer 8

ascending excitation = contraction above bolus. descending relaxation = relaxation below bolus

Question 9

descending pathways: ACh and CGRP actions

Answer 9

either directly, or via cholinergic interneurons: will stimulate release of somatosatin, which inhibits activity of opioid neurons.

Question 10

descending pathways: opioid neurons normally do what? once they are inhibited what happens?

Answer 10

continuous restraint exerted on inhibitory motor neurons. so when inhibited by SST, they’re disinhibited and will cause inhibitory neurons to release PACAP, VIP, ATP, NO = relaxation

Question 11

inteneurons in ascending pathways: release what? regulate what?

Answer 11

likely cholinergic neurons. regulated release of ACh and tachykinins like SP and NKA from excitatory motor neurons

Question 12

ENS neurons classified according to (4)?

Answer 12

function (Afferent, motor, etc.). shape. chemical coding. electrical activity

Question 13

two different shapes of ENS neurons

Answer 13

dogiel type I (less) + type II (lots of processes)

Question 14

intrinsic primary afferent neurons: shape? electrical activity? chemical coding?

Answer 14

dogiel type II. AH neurons. ChAT (so ACh). and CGRP

Question 15

AH neurons meaning and what are an example

Answer 15

“After hyperpolarization”: action potential has a very long after hyperpol. ex: intrinsic primary afferent neurons

Question 16

intrinsic primary afferent neurons: function - what do they sense?

Answer 16

pick up mechanical and chemical signals (like distension, FAs, sugars) as well as 5HT from enterochromaffin cells

Question 17

intrinsic primary afferent neurons: synapse onto (4)?

Answer 17

synapse on each other = self reinforcing circuits. also synapse on ascending interneurons. descending interneurons. motor neurons.

Question 18

interneurons: do what? shape?

Answer 18

conduct impulse to motor neurons. dogiel type I = simpler neuron

Question 19

interneurons: electrical activity?

Answer 19

simple pattern, easily excitable = “S neurons”