enteric nervous system Flashcards
define ENS
network of cell bodies, processes, axons in the wall of GI tract
can work independently of brain
more cell bodies: s.c. or ENS?
ens
what neurons are included in ENS?
neurons within wall of gi tract, axons & terminals of parasymp, symp & visceral sensory neurons that innervate GI tract
myenteric plexus
main neural supply of gut
submucosal plexus (2 functions)
regulate secretion into lumen of GI tract
arterioles for blood flow to mucosa
primary vs secondary vs tertiary plexus (ens)
1: connective nerve trunks between myenteric ganglia
2: nerve trunks that run into circular muscles
3: supply longitudinal muscles
where does ganglionated plexus begin? (submucosal vs myenteric)
sub: pylorus
my: upper oesophageal sphincter (and all the way to anus)
which ens ganglia is bigger?
myenteric (bigger than submucosal)
efferent nerve supply
2 different paths, where do they innervate
sympathetic: entire
parasympathetic: upper & lower
afferent nerve supply
2 different paths, where do they run?, what do they innervate
innervate entire GI tract
vagal: cell bodies in nodose ganglia
dorsal root: run in splanchnic & pelvic nerves
functions of ENS
- movement of intestinal content
- regulation of water & electrolyte transport across mucosa
- control of acid secretion, mucus secretion, bicarbonate secretion
movement of salts and water for homeostasis (2 types)
absorption: lumen -> body
secretion: body -> lumen
describe intestinal movements
when nutrients present in lumen:
localised contractions - then propagate = peristalsis
blockers of intestinal movement (what and how)
- tetrodotoxin: blocks a.p.
- antagonist muscarinic & nicotinic receptors
intrinsic sensory neurons (ens)
sensitive to what
distension, mucosal deformation, presence of nutrients
excitatory motor neurons & inhibitory motor neurons (ens)
what nt’s
to circular & longitudinal muscles (2 types)
e: contract (Ach, SP) i: relax (NOS)
interneurons in ENS (2 types)
Orally: ascending
Anally: descending
secretomotor neurons (ens)
secretion control
vasodilator neurons (ENS)
control diam of art
intestinofugal neurons (ens)
coordinate activities throughout entire ens
interplexus interneurons
communication between 2 plexus
law of the intestine
(what was the experiment, what does this mean?)
contraction ABOVE, relaxation BELOW stimulus
ASCENDING, ORALLY: excitation
DESCENDING, ANALLY: inhibition
top-down approach (ens)
properties neurons must have for behaviours
immunohistochemistry
label for specific neurochemical markers
ganglion = 20 diff neurons
transcriptomics
see what neurons have similar mRNA
how are functions of ens neurons defined?
physiology, projections
properties of ISNs
Properties: primary responders to physiological stimuli, mult. axons to span large areas, chemosensitive to detect nutrients, mechanosensitive channels
do motor neurons allow propagation of motor patterns?
NO
ISN -> local interneurons & motor neurons = _____ projections
polarised projections
how does propagation occur?
descending interneurons connected to ascending interneurons & excitatory motor neurons
therefore anally directed constriction follows relaxation
= propagation
local disruption in neural circuit (ens) -> propagation
produce stationary contractions on either side of disruption
factors altering gut behaviour
chemical composition of contents, volume of contents, viscosity and texture of contents
what does high nutrient content favour in the gut?
segmentation (over propulsion)
large volume of contents triggers?
propulsive contractile patterns and receptive relaxation
= increase speed
low vs high viscosity contents in gut
low: move quick, no deformation of mucosa
high: move slow, mechanical stimulation of mucosa
EE cells
1% of enterocytes -> produce hormones in response to nutrient presence
apical membrane exposed lumen
basal membrane exposed to lamina propria
EC cells
syn, store, release SEROTONIN
respond to chemical and mechno stim (via taste rec or mechanorec)
neuropods
present on what cells, what do they do?
on EE and EC cells
contact terminals of sensory neurons
have proteins involved in transmitter release
blocking serotonin uptake
increasing segmenting motor activity in jejunum
blocking serotonin receptors in mucosa
reduces nutrient induced segmenting motor activity
releasing serotonin from mucosa with cholera tocin
increases propulsive motor activity (rapidly)
can serotonin cross blood brain barrier?
no
Amino Acid Application (onto mucosa)
initiates local reflexes via serotonin and or atp
Amino Acid Application (onto mucosa)
initiates local reflexes via serotonin and or atp
cholinergic secretomotor neuron
process of how it works
Ach -> M3 -> increase Cl- grad
non-cholinergic secretomotor neurons
process
Vip -> AC -> cAMP -> CFTR open
secretion process (ens)
Cl- influx via cftr (tops of villi) -> water and Na+ follow passively
absorption process (ens)
Electroneutral (no direct neural control), constituently active
Na+ transported from lumen into enterocytes (@ tips of villi & mucosal surface of colon)
Via NHE3 sodium hydrogen exchanger (in apical membrane)
Newly differentiated enterocytes -> CFTR
Older enterocytes -> NHE3
Increased speed = Less absorption
diarrhoea from cholera
Diarrhoea results
Activates AC, releases 5-HT from EC cells
Increased propulsive contractions & hypersecretions
Increases excitability of myenteric ISNs = hyperactive
