motor neurons Flashcards
order of skeletal muscle
skeletal muscle –> muscle bundle (fasicle) –> muscle fiber –> myofibril
Schwann cell function
prevents the AP from dissipating away and maintains charge propagating down the axon
active zone
located directly opposite the junctional folds (subneural cleft)
double linear array of synaptic vesicles, 100mM ACh per vesicle
Ca2+ voltage channels lie underside of active zone region
ACh release
via exocytosis when Ca2+ diffuses into terminal
SNARE proteins intertwine and pull vesicle close to membrane
synaptotagmin 1 interacts with calcium and undergoes conformational change which brings vesicle to fuse with membrane
EPP
end plate potential established when ACh binds to NAChR
vesicular fusion
vesicular proteins:
synaptotagmin 1 (located @ vesicle membrane and binds to calcium)
SNARE proteins:
synpatobrevin (located @ vesicle membrane)
SNAP 25 (located @ presynaptic membrane)
syntaxin (located @ presynaptic membrane)
NAChR
activated when two ACh molecules bind
located at crest of junctional fold
allows sodium influx and potassium efflux
sodium voltage gated channel
located at base of junctional fold.
if sodium influx at the NAChR is substantial enough to establish EPP then the sodium voltage gated
sodium voltage gated channel
located at base of junctional fold.
if sodium influx at the NAChR is substantial enough to establish EPP then the sodium voltage gated channel opens and further depolarises the membrane
basal lamina
includes collagen, laminin, proteoglycans, inter alia
ACh esterases
catalyse the breakdown of ACh into acetic acid and choline
choline is transported back to presynaptic membrane and used to synthesise ACh again
2 forms of ACh esterases
- globular
anchored to both pre and post synaptic membrane - asymmetric
anchored to the basal lamina
ACh esterase inhibitors
result in depolarisation block causing paralysis.
drugs include Sarin and VX (venomous agent X)
