neuromuscular junction

Question 1

what is the surface membrane of a skeletal muscle fiber called

Answer 1

sarcolemma…typically one NMJ will be found here

Question 2

what is the neuromuscular jn comprised of

Answer 2

motorneuron and muscle fiber membrane….aka it is the synapse/point of contact b/w 2 excitable cells

Question 3

how does an endplate potential occur

Answer 3

AcH released from the presynaptic neuron bind to AcH receptors in the post synaptic motor end plate. This opens CHEMICALLY GATED Na and K channels. Na gets influxed and there is a little K efflux.

Question 4

properties of the endplate potential

Answer 4

• graded (not all or none)
• DON’T PROPOGATE
• amplitude is only -10mV (whereas a.p is ~130mV)

Question 5

what is a miniature endplate potential

Answer 5

small endplate potential that occurs when there is the release of ACh from ONE vesicle. these OCCUR SPONTANEOUSLY, they are still confined to the endplate region (don’t propogate), and there amplitude is only ~1-2mV.

Question 6

what is the role of acetylcholinesterase

Answer 6

breaks down ACh.

Question 7

where is acetylcholinesterase located

Answer 7

in the motor endplate membrane (postsynaptic neuron) in AND in the basal lamina

Question 8

what happens to the breakdown products of ACh

Answer 8

1. acetic acid/acetate re-enters circulation

2. choline enters the presynaptic terminal where is reacts with acetyl-coA to create more ACh

Question 9

what enzyme combines acetyl-coA and choline in the presynaptic terminal

Answer 9

choline acetyltransferase

Question 10

what are the effects of curare

Answer 10

binds to NICOTINIC ACh receptors so that ACh can’t bind and no muscle AP will occur

Question 11

what are the effects of botulinum toxin

Answer 11

blocks the release of ACh from the presynaptic neuron so that skeletal muscle a.ps can’t occur= FLACCID PARALYSIS

Question 12

what are the effects of organophosphates

Answer 12

blocks the action of the acetylcholinesterase so that ACh will not be broken down. At first, there will be spastic paralysis (sustained state of contraction) bc constant presence of ACh. Eventually, there will be flaccid paralysis bc Na channels at the postsynaptic terminal will always be in the refractory state, and the skeletal muscle will no longer be able to the activated and muscle will begin to breakdown