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46 Cards in this Set
- Front
- Back
Describe the organization of ENS, from innermost to outermost
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lumen
mucosa mucosal plexus muscularis mucosa submucosa meissner's plexus circular muscularis externa myenteric plexis longitudinal muscularis externa |
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T/F
The enteric system contains as many cells as the spinal cord |
TRUE
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T/F
When isolated from CNS, ENS may still coordinate basic reflexive function of secretion, absorption, & mixing & movement of luminal contents |
TRUE
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What are the two neuronal networks of the ENS?
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1. Myenteric (Auerbach's Plexus)
2. Submucosal (Meissner's Plexus) |
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The ENS recieves input from (parasympathetic/sympathetic) neurons
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BOTH parasympathetic & sympathetic
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(myenteric/submucosal) extends through the entire GI tract
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myenteric
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(myenteric/submucosal) is limited to the small and large intestine
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submucosal
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Plexus organized into ganglia contain (one/many) cells.
___________ interconnect ganglia & plexus |
many (btwn 5-10 up to hundreds)
nerve bundles |
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Neuronal cells w/i the ENS have ______and _________ axons, and contain _______ of the CNS (not periphery)
There are ___ neuronal cell types w/i ENS |
fine and umyelinated axons
glia 15 |
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Sensory neurons of the ENS respond to 2 kinds of stimuli:
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mechanoreceptors
chemoreceptors |
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What are the 4 mechanisms of sensory neuron projection?
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1. Intrinsic confined to ENS (IPAN: intrinsic primary afferent neurons)
2. Projection via vagus to brainstem (vagal primary afferents) 3. Nociceptive projection to sympathetic ganglion (intestinofugal neurons) 4. Projection via dorsal root to spinal cord (spinal primary afferent) |
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What do intermediary epithelial cells secrete in response to luminal pH, inorganic acids, short chain fatty acids, toxins, ect?
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serotonin
(5-HT) |
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What does serotonin do?
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activates sensory cells
*many sensory cells respond to multiple stimul types = polymodal |
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Excitatory motor neurons act on smooth muscle via intermediary cells known as, ________________________
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interstitial cells of Cajal (ICC)
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Interstitial cells of Cajal (ICC) are non-neuronal, pacemaker cells, that are electrically coupled to what?
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unitary smooth muscle units
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What are the excitatory transmitters that act via metabotropic receptors?
What else is released? |
Ach & tachykinin
Opoids & GABA |
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Transmitters act on autoreceptors to negatively feedback on motornuerons, what is the result of this?
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reduced transmission
(via this pathway that opiates induce constipation) |
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Inhibitory motor neurons also act on smooth muscle via ICC. What are the inhibitory transmitters?
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NO, ATP, vasoactive intestinal peptide & pituitary adenyl cyclase activating peptide
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_______________oscillation is propagated into smooth muscles, giving rise to passive oscillations in the muscle called, ___________
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ICC Vm oscillation
slow waves |
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T/F
Enteric input changes frequency & amplitude of slow waves |
FALSE
enteric input does NOT change frequency (only amplitude) |
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If slow waves are ____________ no muscle contraction occurs
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subthreshold
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Slow waves propagate in the _____________ direction.
What does this result in? |
rostro-caudal direction
resulting in a delay from one depolarized zone to the next |
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Enteric input shifts ___________ and consequently _____ oscillations in muscle
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potential and consequently Vm oscillations
(**does not shift pacemaker freq of ICC) |
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Secretions in GI & exocrine glands depend on what?
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water from blood
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Neurons innervate smooth muscle of arteriole & crypts of Lieberkuhn, they induce __________ by the crypts and by osmosis induce ___________
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Cl- secretion by crypts
osmosis induce water excretion |
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In stomach, action of _________is on parietal cell to do what?
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secretomotor vasodilators
induce gastric acid secretion |
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What is the secretomotor response to noxious stimulants?
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-stimulus depolarizes epithelial cell resulting in serotonin & prostaglandin synthesis & release
-these activate IPAN & induce Cl- secretion -results in diarrhea & massive fluid loss |
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How does Cholera toxin lead to death?
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permanently activates IPAN & induces Cl- sectretion via adenyl cyclase, leads to diarrhea & massive fluid loss which eventually cause dehydration & death
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How does the enteric system regulate gastrin release?
what does gastrin do? |
-G cells in gastric antrum recieve parasympathetic input (food smell, etc) from enteric neurons via vagus nerve, GRP (gastrin-releasing peptide) induces gastrin release.
-gastrin induces acid secretion by parietal cells (*Pavlov) |
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What types of interneurons are w/i the ENS?
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-ascending
-descending -interconnecting (btwn myenteric & submucosal) |
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How do preganglionic cells from the parasympathetic reach ENS?
How do postganglionic cells reach ENS? |
preganglionic project via vagus & pelvic nerve (from sacral spinal cord) into enteric
postganglionic are w/i ENS |
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How do the cholinergic parasympathetic cells affect ENS?
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increase vasodilation, secretory activity, and peristaltic movement
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Describe GI motility
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-propulsion (peristalsis) moves content caudally
-segmental contraction mixes content w/ digestive enzymes -migrating motor complexes (MCC) of small intestine clean lumen & shed epithelial cells btwn meals -opening & closing of sphincters *enteric involved in all |
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Describe propulsive movement
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circular muscle above bolus contract & circular muscle below relax, pushing bolus down from oral cavity toward anus
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Steps of Propulsive movement
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1. IPAN responds to distension, activating chain of ascending & descending interneurons
2. Ascending contact exitatory motorneurons that induce contraction of circular muscle via ICC 2. Descending contact inhibitory motorneurons that induce relaxation of circular muscle via ICC 3. Excitation & inhibition impacts amplitude with changes contraction level by altering # of action potentials |
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T/F
Since the upper 1/3 of esophagus is surrounded by skeletal muscle, enteric neurons do not modulate |
FALSE
enteric neurons DO form synapses on motor end plate & modulate synaptic activty in upper esophagus! |
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Distension due to bolus & chemical stimulus also induces local _________
How does this occur? |
local secretomotor activity
-stimulated IPAN activates descending interneurons -interneurons activate secretomotor neurons -secretomotor neurons induce vasodilation & Cl- secretion into lumen -Cl- secretion induces water movement into lumen |
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When pyloric sphincter is closed, gastric peristalsis results in ________ via ______________
What is gastric peristalsis due to in this case? |
churning
via migrating motor compex (MMC) due to ICC (enteric excitatory motor neurons not essential) |
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All sphincter w/i the GI tract are controlled by the ENS except for which 2?
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esophageal & external rectal sphincters
(skeletal muscles) *esophageal control mostly vagal *external rectal somatic |
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What enterically controlled sphincter controls the passage of bile from gallbladder & pancreas into deodenum?
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sphincter of Oddi
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Describe the 3 actions involved in the rectosphincteric reflex?
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1. fecal matter stretches/stimulates internal rectal sphincter to open (ENS)
2. opening of internal sphincter leads to increased motor activty from (PNS, sacral spinal cord neurons) 3. external rectal sphincter can be opened voluntarily (CNS) |
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Short reflexes, such as the entero-enteric reflex occur how?
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one caudal segment of intestine can modulate activity in a more rostal segment (LOCAL) via ascending interneurons
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Long reflexes, such as the enterogastric reflex occur how?
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emptying of stomach into duodenum is regulated by 1. a long distance ascending interneuron (DISTANT) & 2. a sympathetic duodenum-paravertebral ganglion stomach pathway
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How is the enterogastric (long) reflex induced (3 ways)?
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1. distention of duodenum
2. pH in duodenal chyme 3. osmolarity of duodenal chyme 4. irritants in duodenum 5. presence of certain digestive breakdown enzymes in duodenal chyme |
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General motor activity of the intestine is also regulated by ____________ input
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sympathetic input
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How does the sympathetic system affect the enteric system?
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-postganglionic cells project from paravertebral or prevertebral
-noradrenergic -inhibit secretion & motility -vasoconstriction -sensory neurons (intestinofugal) project to prevertebral ganglion to modulate secretion & motility inhibition |