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Flashcards in MSK - NMJ Deck (54)
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1

what innervates skeletal muscle?

fast conducting alpha motor neurons with myelinated axons and cell Bodies in the spinal cord or brain stem

2

where does the axon divide into unmyelinated branches?

near the muscle to innervate individual muscle fibres

3

what is the motor unit?

the neurone and the number of fibres it innervates

4

what is the end of the branches?

terminal bouton that synapses with the muscle membrane at NMJ

5

what does an action potential cause?

release of transmitter Ach

6

where exactly is the synapse?

endplate region of skeletal muscle fibre

7

what contains the Ach?

synaptic vesicles which cluster at active zones

8

where are the nicotinic Ach receptors?

junctional folds that face the active zones

9

where is Ach synthesised?

cytoplasm of bouton

10

where is Ach stored?

synaptic vesicles

11

how is Ach released from the vesicles into the clefts?

Ca2+ dependant release by exocytosis

12

what happens once Ach is released?

brief activation of nicotinic receptors by reversible binding

13

what terminated the binding of Ach?

acetylcholinesterase

14

what terminates the binding of Ach?

acetylcholinesterase

15

pre-synpatically, how is choline transported into the terminal?

choline transporter (symport with Na+)

16

what is combined to produce Ach and by which enzyme?

choline and acetyl coenzyme A
choline acetlytransferase

17

what concentrates Ach in the vesicles?

vesicular Ach transporter

18

what does arrival of the action potential at the terminal cause?

depolarisation
opening of voltage gated Ca2+ channels
Ca2+ entry to the terminal

19

what does Ca+ cause the docked vesicles to do?

undergo exocytosis

20

how many ACh molecules activate each nicotinic receptor?

2

21

what are nAChRs?

pentamers of glycoprotein subunits surrounding a central cation selective pore

22

when does the pore/gate open?

when ACh binds

23

what is the channel equally permeable to and not permeable to?

Na+ and K+
anions

24

what happens when the gate is open?

Na+ enters and K+ exits simultaneously

25

how is a depolarising end plate potential generated?

influx of Na+ is greater (driving force at resting potential)
simultaneous opening of many nAChrs

26

what does each vesicle of Ach contain?

a quantum of neurotransmitter

27

what is a miniature end plate potential?

the electrical response to one quantum of transmitter

28

what is the graded electronic response?

when many MEPPs summate to produce an end plate potential

29

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

30

what causes the contraction once the action potential is released?

release of Ca2+ from intracellular stores