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Neurotransmitter removal
Explore the process of neurotransmitter removal from the synapse. Learn how action potentials trigger neurotransmitter release, and why high-frequency firing can lead to neurotransmitter buildup. Discover the roles of diffusion, enzymes, re-uptake pumps, and astrocyte endfeet in maintaining synaptic function and facilitating neuron-to-target cell communication. Created by Matthew Barry Jensen.
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can you run out of nuerotransmitters by firing to many action potentials?(11 votes)
Under normal conditions you cannot run out of neurotransmitter. Although some drugs increase the transmitter release/ inhibit the re-uptake which could have some heavy side effects.(8 votes)
if i understood it correctly there are astrocytes covering the open spaces on the sides of the synaptic cleft. How can neurotransmitters diffuse out of that complex of cells and NOT get either into an astrocyte, back into an axon or in a receivermolecule ?
And on enzymes breaking down neurotransmitters in the synaptic cleft : they wil start doing that the moment neurotranmitters are present, in theory before they could reach the receiving cell. When there is only a mild signal to start with, that process could lead to not giving over any information to the target cell.. could you please shed some light on that thought ?(7 votes)
I had the same thought about the astrocytes covering the open spaces. But you also need to think that the picture was drawn in 2D while it occurs in 3D. Also, I'm pretty sure the size of the neurotransmitters are quite small compared to the spaces available for diffusion. So while astrocytes probably can hinder diffusion, it's probably a small hinderance. Either way, this is why there are multiple mechanisms for neurotransmitter removal.(5 votes)
what is the name of enzyme that break down the neurotransmitters ?(5 votes)
AchE: Acetyl Choline Esterase for Ach. There are other enzymes for different NT.(6 votes)
- In video, it is stated that neurotransmitters need to be removed so the subsequent information can be transferred properly. So why - as stated in question hints - SSRI (Selective Serotonin Reuptake Inhibitors) - function by blocking uptake of the serotonin to actually allow serotonin to be present. Wouldn't it be counter-productive not to clear the synapse?(5 votes)
To my understanding, SSRI is used as an antidepressant, a condition where serotonin quantity is relatively low; a NT required for "feelings of well being and happiness". Here itself the level of serotonin is low from the beginning hence these SSRIs help by blocking the reuptake of serotonin plus it also blocks the pump on astrocyte's end feet.
I am waiting for better answers though.(5 votes)
Do all of the active methods of removing neurotransmitters require ATP?(3 votes)
Yes, otherwise they would not be "active"(3 votes)
So what exactly happens on the outside of one's body (physically) when all of these methods of removal fail to work and the synapse is no longer working? I understand that it can be different for different synapses and different receptors but does anyone have an example?
Thanks!(2 votes)
If acetylcholine removal from the synapse is inhibited, it's accumulation at the neuromuscular junctional synapse may cause paralysis of the muscle. This is the mode of action of some neurotoxins. Sometimes, in some diseases where acetylcholine is able to bring about the requisite function (causing weakness) we artificially inhibit it's removal from the synapse to prolong it's effect and to allow for normal functioning (ex: in Myasthenia Gravis).(3 votes)
- I dont understand how the lingering of a neurotranmitter in the synaps effect the transmission of new action potentials ? Can someone please elaborate on that?1:12-1:33(1 vote)
- I am not sure that I can explain this in the same way this instructor thinks about it. From my view, basically, the neurons must "turn on and off", that is, they must send action potentials and stop sending action potentials in order to manage the body, or relay information in the brain. Let's think about the heart as an example. We have the heart beating automatically, but it changes its rhythm with the input of the parasympathetic n. s.'s neurotransmitter, acetylcholine which slows it down and the sympathetic n. s.'s adrenalin (epinephrine) which speeds it up. Can you imagine that if the adrenalin did not degrade and the heart's muscle fibers had more and more adrenalin then they would beat faster and faster? In fact they could contract so fast the ventricles would not have time to fill with blood, so the heart would not be moving blood. And the opposite could happen with too much acetylcholine in the synapse. Imagine that acetylcholine was not degraded and it remained at the synapses of the heart muscle fibers. Now, the heart would slow down to the point of not contracting and once again , the heart is not doing its job of pumping blood. In fact, that is the pathology of insecticides and nerve gas, to increase the amount of acetylcholine at multiple synapses in the body, causing death. Neurons must flood the synapse with neurotransmitter, for the action potential to occur and the neurotransmitter must be removed for the action potential to stop. I hope this helps.(4 votes)
- what is the pump name of the astrocytes ? astrocytes pump ?? and what conditions that determine neurotransmitters will be break down inside the astrocytes OR it should transferred back to the axon terminal ?(2 votes)
I think the neurotransmitters are re-uptaken phagocytically by the astrocytes after the action potential signal has been propogated.(1 vote)
In this video, are we talking about the extra neurotransmitter's that didn't get bind to NT receptors? If so, what happens to the neurotransmitter's that are bound to the NT receptors? Do they also get removed through the mentioned mechanisms?
Thank you.(2 votes)- do astrocytes have pumps or do they act like phagocyte, thus engulfing the neurotransmitters?(2 votes)
- Yes you are exactly right! The astrocyte uptake the neurotransmitters releases into the synaptic cleft once the action potential has been propagated to the soma of the next neuron.(1 vote)
1:12Video transcript
In this video, I wanna talk about how neurotransmitters are removed from the synapse. In other videos, we've talked about how action potentials travel down axons, and the information that's contained in action potentials, is really contained in the frequency of action potential firing, and the duration of a
train of action potentials. And when the action potential
reaches the axon terminal, at the end of the axon, neurotransmitters are released
into the synaptic cleft to bind to neurotransmitter recepters on the target cell. But if a neuron is
firing action potentials very frequently, if there are large numbers
of action potentials reaching the axon terminal, then the rate of neurotransmitter release into the synapse, may exceed the rate that neurotransmitter can just passively diffuse
out of the synapse, so that diffusion is the first method by which neurotransmitter can be removed from a synapse, "Diffusion." But, that only works if the
neuron is firing action potentials at a slow frequency. At a fast frequency,
diffusion won't be enough, and there'll be a build up of neurotransmitter in the synapse. And this would be a problem, because if the neurotransmitter
is just lingering in the synapse, then
neurotransmitters bound the neurotransmitter
receptor, most of the time, and the information
contained in the frequency, and the duration of trains
of action potentials, wont' be able to be
transmitted to the target cell. The synapse will basically
not be functional, to communicate additional information. Therefore, neurotransmitter may need to be actively removed, instead of just through passive diffusion, to
clear out the neurotransmitter from the synaptic cleft. And it turns out that
there are several ways that this happens. The first of these active methods, or the second method to
remove neurotransmitter from the synapse, are
enzymes that can break down the neurotransmitter in the synapse. So certain synapses contain
enzymes that'll actually break down the neurotransmitter
into its component parts, which are no longer able to stimulate the neurotransmitter receptor. So they're removing
active neurotransmitter from the synapse. The next active method, is that
some pre-synaptic membranes contain special pumps, special
active transport channels, that actively pump back
in the neurotransmitter, into the axon terminal, where it's often recycled, to
be used for a subsequent round of neurotransmission, by being released back into the synapse. So these pumps are
called "Re-uptake Pumps," because they take the
neurotransmitter back into the axon terminal where it came from in the first place. By doing so, they remove
the neurotransmitter from the synaptic cleft. Another big method of actively
removing neurotransmitter from the synapse, is
by "Astrocyte Endfeet." So the astrocytes in the
central nervous system put their endfeet on lots of the synapses in the central nervous system, and they also have pumps
at a lot of these synapses, that can actively pump
the neurotransmitter out of the synapse, into the astrocyte. And sometimes it'll just be broken down, or used in the astrocyte,
or sometimes the astrocyte will actually transfer
some of the substances of the neurotransmitters
back into the axon terminal of the neuron, where it will
be recycled, and used again for neurotransmission. So all of these different
methods allow the synapse to basically be rapidly turned on and off. 'Cause neurotransmitter
can be rapidly released into the synaptic cleft, and then it can be rapidly cleared out, so that the synapse is capable
of conveying more information from the neuron, to the target cell.