Flashcards in MSK - NMJ Deck (54)
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?
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?
what terminates the binding of Ach?
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
what concentrates Ach in the vesicles?
vesicular Ach transporter
what does arrival of the action potential at the terminal cause?
opening of voltage gated Ca2+ channels
Ca2+ entry to the terminal
what does Ca+ cause the docked vesicles to do?
how many ACh molecules activate each nicotinic receptor?
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+
what happens when the gate is open?
Na+ enters and K+ exits simultaneously
how is a depolarising end plate potential generated?
influx of Na+ is greater (driving force at resting potential)
simultaneous opening of many nAChrs
what does each vesicle of Ach contain?
a quantum of neurotransmitter
what is a miniature end plate potential?
the electrical response to one quantum of transmitter
what is the graded electronic response?
when many MEPPs summate to produce an end plate potential
what is the condition for the end plate potential to cause contraction?
all or none reaction
it must exceed threshold to trigger contraction but this always occurs normally