AAMC BIO Q-pack Neurobio Question

[jmu29]

I am pretty good with neurobiology and I know the answer I picked is wrong but the explanation is a little tricky. it says a cholinesterase blocker would cause an act buildup in the synapse and prevent receptors from responding to impulses. this didn't make sense to me because isn't this the purpose of SSRI's? to increase neurotransmitter concentration at the synapse so that you can get MORE of a response?

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[JimKimSlim]

You have to pay attention to the word “repeated transmission” of impulse. After an action potential is generated in the post synaptic neuron, acetylcholine is cleared through the enzyme, diffusion, or absorption so that the receptors will be ready to respond to the next incoming impulse. By blocking cholinesterase, there are less binding sites available for the next wave of acetylcholine and can’t sustain the repeated transmission of impulse.

 

[jmu29]

You have to pay attention to the word “repeated transmission” of impulse. After an action potential is generated in the post synaptic neuron, acetylcholine is cleared through the enzyme, diffusion, or absorption so that the receptors will be ready to respond to the next incoming impulse. By blocking cholinesterase, there are less binding sites available for the next wave of acetylcholine and can’t sustain the repeated transmission of impulse.

This is what I was thinking. But that is kind of what is confusing me. Even though the enzyme is absent, ACH can still diffuse away or be reabsorbed. Therefore, it wouldn't affect repeated transmission? Or is it that fact that in this specific process the ONLY way ACH is cleared is via enzyme?

 

[JimKimSlim]

This is what I was thinking. But that is kind of what is confusing me. Even though the enzyme is absent, ACH can still diffuse away or be reabsorbed. Therefore, it wouldn't affect repeated transmission? Or is it that fact that in this specific process the ONLY way ACH is cleared is via enzyme?

I think you’re focusing too much on the alternatives that weren’t mentioned on the question stem. My thought process was blocking ACE = more acetylcholine in the synapse = less binding site available for the incoming impulse = weak transmission. I was a biochemistry major and had the same issue, where I had more knowledge than others. Then, I realized that not everyone took cellular biology or bio-organic chemistry like I did. You should always approach problems within the frame of the question and don’t bring outside knowledge that are not mentioned in the question stem. Also, choice c is the better answer because it’s very clear that more receptors will improve transmission.