Bubblybabybling
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Why is it needed?
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Eloades11
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(Original post by Bubblybabybling)
Why is it needed?
This isn't too hard of a question, and you probably could have saved some time if you just googled it. Acetylcholinesterase (AChE) is an enzyme that catalyzes the breakdown of acetylcholine esters that function as neurotransmitters. It is located on the post-synaptic membrane of neuromuscular junctions and it breaks down acetylcholine in the synaptic cleft to prevent it from continuously activating the receptors.
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thegodofgod
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(Original post by Bubblybabybling)
Why is it needed?
As above.

Interestingly, acetylcholinesterase (AChE) is a target for 3 out of the 4 drugs that are licensed for use in mild-moderate Alzheimer's disease (AD): donepezil, galantamine, and rivastigmine. This is because there is thought to be a decrease in the number of functioning cholinergic neurons (neurons that release acetylcholine (ACh) as their neurotransmitter) in AD, and so the inhibition of AChE by these drugs would inhibit the breakdown of the ACh that is released by these cholinergic neurons, so more ACh is available to act on its post-synaptic receptors.
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mice8cheese
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Acetylcholine is used as the transmitter in the parasympathetic nervous system, so in terms of heart rate, making sure that it is broken down is also important in that respect.
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z33
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because without is the acetylcholine will be stuck to the post synaptic knob and keep firing
if you break it down you can recycle the acetylcholine and prevent overstimulation/ muscle fatigue
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rileystringer1
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(Original post by mice8cheese)
Acetylcholine is used as the transmitter in the parasympathetic nervous system, so in terms of heart rate, making sure that it is broken down is also important in that respect.
neurotransmitter^
don't agree with this though

the role of the parasympathetic nervous system and the 'rest or digest' phase in relation to heart rate is simply that it is slowed down because you don't need as much oxygen as quickly as you would during fight of flight

if acetylcholine wasn't broken down, the heart rate wouldn't just keep falling until it eventually stops, would it?
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mice8cheese
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(Original post by rileystringer1)
neurotransmitter^
don't agree with this though

the role of the parasympathetic nervous system and the 'rest or digest' phase in relation to heart rate is simply that it is slowed down because you don't need as much oxygen as quickly as you would during fight of flight

if acetylcholine wasn't broken down, the heart rate wouldn't just keep falling until it eventually stops, would it?
Ordinarily, the pacemaker potential results in a spontaneous signal so that the heart beats in response to the action potentials that are automatically generated in the SA node. When less sodium and calcium ions enter, the action potential is generated slower, decreasing the rate at which the SAN fires.

Parasympathetic nerve fibres originate in the cardioinhibitory centre and reach the SAN via the vagus nerve. Acetylcholine is used as a neurotransmitter, decreasing pacemaker rate by increasing potassium and decreasing calcium and sodium movement. This slows the rate at which the SAN fires, decreasing the heart rate.

If acetylcholine is not broken down, the heart rate will slow down, as potassium
will continue to leave the SAN at a faster rate, and calcium and sodium will continue to enter the SAN at a slower rate. This will not cause the heart to stop beating, as the action potential will still be generated, just slower.

If the heart rate gets too slow, cells will not get sufficient oxygen, the triggering sympathetic nervous system to increase the heart rate, as a negative feedback mechanism.

Or at least the last two paragraphs would be my guess. If that isn't how it works, and it really does just stop the heart from beating, then evolution seriously missed a trick.
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thegodofgod
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(Original post by rileystringer1)
neurotransmitter^
don't agree with this though

the role of the parasympathetic nervous system and the 'rest or digest' phase in relation to heart rate is simply that it is slowed down because you don't need as much oxygen as quickly as you would during fight of flight

if acetylcholine wasn't broken down, the heart rate wouldn't just keep falling until it eventually stops, would it?
A major reason is to prevent tachyphylaxis - where there is a rapid decrease in response to a drug, which can occur after a series of small doses (which could be as a result of acetylcholine not being metabolised by acetylcholinesterase, and thus it would keep on binding to the receptors and activating them) (Macfarlane and Koppanyi, 1970).

This would effectively mean that further parasympathetic stimulation would not cause a further decrease in heart rate, which is important to know, as it is the parasympathetic nervous system - not the sympathetic nervous system - which is mainly active at rest.

Macfarlane MD, Koppanyi T (1970). Acetylcholine tachyphylaxis in isolated rabbit atrium and its relation to norepinephrine stores. J Pharm Sci 59(9):1252-1255.
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rileystringer1
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(Original post by thegodofgod)
A major reason is to prevent tachyphylaxis - where there is a rapid decrease in response to a drug, which can occur after a series of small doses (which could be as a result of acetylcholine not being metabolised by acetylcholinesterase, and thus it would keep on binding to the receptors and activating them) (Macfarlane and Koppanyi, 1970).

This would effectively mean that further parasympathetic stimulation would not cause a further decrease in heart rate, which is important to know, as it is the parasympathetic nervous system - not the sympathetic nervous system - which is mainly active at rest.

Macfarlane MD, Koppanyi T (1970). Acetylcholine tachyphylaxis in isolated rabbit atrium and its relation to norepinephrine stores. J Pharm Sci 59(9):1252-1255.
So I was right in thinking that acetylcholine not being broken down wouldn't cause the heart to stop beating

Thanks guys
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