1.08 Gut Function + Innervation Flashcards
What plexus is responsible for control of secretory functions, absorption, and blood flow?
Submucosal plexus
What plexus is responsible for control of motility regulating circular and longitudinal muscle?
Myenteric plexus
What is the origin of parasympathetics in GI tract?
Medulla oblongata = CNX
Sacral spinal cord = pelvic splanchnic nerves
What is the role of parasympathetics in GI?
Increase motility, secretions, blood flow, and relaxation of sphincters
What organs do the cranial division of the parasympathetics innervate?
Esophagus, stomach, small intestine, large intestine (cecum, ascending, and proximal 2/3 transverse)
What kind of receptors are the postganglinic neurons terminateing on smooth muscle or glans within the parasympathetic system?
Muscarinic
What neurotransmitter is used for the parasympathetics?
Ach
What kind of receptor is present when Ach is released from the preganglionic vagus nerve to the submucosal or myenteric plexus?
Nicotinic
What organs are innervated by the parasympathetic sacral division?
1/3 transverse colon, descending, sigmoid, rectum, anal canal to sphincter
What sacral levels do the parasympathetic pelvic splanchnic nerve arises?
S2-S4
Where do the postganglionic neurons of PARA originate?
Terminal ganglia of myenteric/submucosal plexus
What are the neuron structure/trends of the PARA pre and post ganglionic neurons?
Pre = long, myelinated , fast
Post = short, unmyelinated, slow
What is the difference between nicotinic and muscarinic receptors?
Nicotinic = ligand gated ion channels
Muscarinic = GPCR
What spinal levels do the sympathetic nerves originate from?
T5-L2 (thoracolumbar nerves)
What is the sympathetic innervation relationship to sphincter muscle?
Inhibitor to non-sphincter
Excitatory to sphincter (contract)
What are the sympathetic roles to digestion?
Decrease motility, secretions, blood flow (vasoconstrict) and contract sphincters
What are the neuron structure of pre and post ganglionic neurons in the sympathetic system?
Pre = short, myelinated, fast
Post = long, unmyelinated, slow
What neurotransmitters do the pre and post ganglionic neurons release in SYM?
Pre = Ach
Post = NE
What are the sympathetic prevertebral ganglia?
Celiac, superior mesenteric, inferior mesenteric
The release of NE from postganglionic SYM neuron to what receptor allows for smooth muscle relaxation?
B2
The release of NE from postganglionic SYM neuron to what receptor allows for sphincter contraction?
A1
The release of NE from postganglionic SYM neuron to what receptor allows for secretion suppression?
A2
The release of NE from postganglionic SYM neuron to what receptor allows for vessel vasoconstriction?
A1
What kind of neurons are confined to the enteric nervous system as a single axon with multiple branches to detect mechanical, chemical, and thermal changes?
IPANs (intrinsic primary afferent neurons)
What NT do IPANs release?
Ach to Muscarinic receptors
Substance P to Neurokine receptors (NK)
IPANs communicate to what I order to integrate reflex control of gut function?
Interneurons (plexuses)
IPANS communicate to what in order to get immediate response for smooth muscle contraction or glandular secretion?
Motor neurons
Ascending IPANs (oral direction) do what to motor neurons for peristaltic propel?
Activate excitatory motor neurons
Descending IPANs (anal direction) activate what in order to relax smooth muscle downstream?
Inhibitory motor neurons
What is the interneuron structure?
Multipolar with multiple dendrites and axons
What neurotransmitter is released by SENSORY IPANs to interneurons?
Serotonin (5-HT) = excitatory (fast = 5-HT3 vs prolonged 5-HT4)
Interneurons release what in excitatory pathways to motor neurons?
Ach
(To N2 = smooth mm contract)
Interneurons release what to descending pathways/motor neurons to mediate smooth muscle relaxation?
NO
(to soluble guanylyl cyclase)
What is the neuron structure of motor neurons in the ENS?
Multipolar extensive dendrites
What are the four kinds of motor neurons in the ENS?
- Excitatory
- Inhibitory
- Secretomotor
- Vasodilator
Key NT for excitatory motor neurons and their receptors?
Ach to M3/M2
SubP to NK1/NK2
Inhibitory motor neuron NT and their receptors?
NO = soluble guanylyl cyclase
VIP = VPAC1/VPAC2
Secretory motor neuron NT and their receptors?
Ach = M3
VIP = VPAC1/VPAC2
Vasomotor motor neurons Nt and their receptors?
VIP = VPAC1/VPAC2
NO = sGC
What is the SIP syncytium and what is it made up of?
Smooth muscle cell network
1. Smooth muscle cells (S)
2. Interstitial cells (ICCs)
3. PDGFRa+ cells
What are ICCs?
Pacemakers that generate SLOW waves to set baseline rhythm
What mediate inhibitory signals from enteric motor neurons and are responsive to NO and VIP?
PDGFRa+ cells
What is the structure of ICC?
Spindle shaped with long processes
What is the excitatory NT for ICCs?
Ach = M3 (to increase intracellur calcium of smooth muscle cells)
SubP = NK1
What are the ICC inhibitory NTs?
NO = sGC
VIP = VPAC1
What are the key NT and receptors for PGFRa+ cells?
NO (sGC) and VIP (VAPC1)
Although PDGFRa+ cells also use gap junctions to propagate its effects onto smooth muscle cells, how is it different from ICC inhibitory functions?
It does not produce waves
In what directions are the ICC and PDGFRa+ cells more involved?
Ascending - oral - excitatory ICC
Descending - anal - inhib med PDGFRa+
What can help diagnose gastrointestinal motility disorders in biopsy (gastroparesis, chronic constipation, and intestinal pseudo obstruction) ?
Reduced ICC density
Targeting NO or VPAC on what cells may improve smooth muscle relaxation and gut function in conditions like achalasia, functional obstruction, or plastic disorders ?
PDGFRa+
