Bio: ACH question

[joonkimdds]

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Which statement about acetylcholine is NOT true?
A. ACH is released at the neuromuscular junction.
B. ACH binds to specific receptors on the postsynaptic
membrane.
C. In a synaptic cleft there are enzymes that degrade
ACH.
D. ACH diffuses through the pre-synaptic
membrane after its synthesis.
E. A synapse that is subjected to many action
potentials may be depleted of ACH granules.


First of all, I know A,B, and C are true.

I don't know why D is wrong. Is it because diffusion means it goes from high to low concentration? If it uses vesicle and gets exocytosed (I think that's the correct term used here?), does it not count as diffusion?

And what's is E trying to say? Is it related to what C is saying?

 

[pbure9]

Right, D is wrong because it's not diffusion from the presynaptic membrane, but exocystosis (triggered by the Ca++ ions) as you mentioned.
E is strange, I would say if theyre trying to say that if a cell has too many action potentials you deplete you're ACh granules since you release a lot of ACh...??? I guess that's possible. But D is definitely not true.

 

[joonkimdds]

Right, D is wrong because it's not diffusion from the presynaptic membrane, but exocystosis (triggered by the Ca++ ions) as you mentioned.
E is strange, I would say if theyre trying to say that if a cell has too many action potentials you deplete you're ACh granules since you release a lot of ACh...??? I guess that's possible. But D is definitely not true.

But isn't it why we have the enzyme to degrade ACH and put it back to where it came from? so I thought that ACH can be recycled forever~!🙄

 

[razblo]

I would say it's D because the way I'm interpretting the answer is that it just diffuses from the soma down the axon. In reality I believe neurotransmitters get made (at least part of them) and packed into vesicles in the soma and they travel down the axon, by way of force generating proteins, to the pre-synaptic terminal.

 

[pbure9]

But isn't it why we have the enzyme to degrade ACH and put it back to where it came from? so I thought that ACH can be recycled forever~!🙄

yea i was thinking that too.. but if aceytlcholinesterase is inhibited or cant keep up with the amount of action potentials being produced, that would deplete acetylcholine granules. Thats just an example, but in reality, many action potentials will release more and more ACh into a synapse, so I would eliminate E.

And its not diffusion, its released through vesicles