MSK - NMJ Flashcards
(54 cards)
what innervates skeletal muscle?
fast conducting alpha motor neurons with myelinated axons and cell Bodies in the spinal cord or brain stem
where does the axon divide into unmyelinated branches?
near the muscle to innervate individual muscle fibres
what is the motor unit?
the neurone and the number of fibres it innervates
what is the end of the branches?
terminal bouton that synapses with the muscle membrane at NMJ
what does an action potential cause?
release of transmitter Ach
where exactly is the synapse?
endplate region of skeletal muscle fibre
what contains the Ach?
synaptic vesicles which cluster at active zones
where are the nicotinic Ach receptors?
junctional folds that face the active zones
where is Ach synthesised?
cytoplasm of bouton
where is Ach stored?
synaptic vesicles
how is Ach released from the vesicles into the clefts?
Ca2+ dependant release by exocytosis
what happens once Ach is released?
brief activation of nicotinic receptors by reversible binding
what terminated the binding of Ach?
acetylcholinesterase
what terminates the binding of Ach?
acetylcholinesterase
pre-synpatically, how is choline transported into the terminal?
choline transporter (symport with Na+)
what is combined to produce Ach and by which enzyme?
choline and acetyl coenzyme A
choline acetlytransferase
what concentrates Ach in the vesicles?
vesicular Ach transporter
what does arrival of the action potential at the terminal cause?
depolarisation
opening of voltage gated Ca2+ channels
Ca2+ entry to the terminal
what does Ca+ cause the docked vesicles to do?
undergo exocytosis
how many ACh molecules activate each nicotinic receptor?
2
what are nAChRs?
pentamers of glycoprotein subunits surrounding a central cation selective pore
when does the pore/gate open?
when ACh binds
what is the channel equally permeable to and not permeable to?
Na+ and K+
anions
what happens when the gate is open?
Na+ enters and K+ exits simultaneously
