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Current time:0:00Total duration:3:47

Video transcript

in this video I want to talk about how neurotransmitter is 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 neurotransmitter is released into the synaptic cleft to bind to neurotransmitter receptors 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 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 buildup of neurotransmitter in the synapse and this would be a problem because if the neurotransmitter is just lingering in the synapse then neurotransmitter is bound to the neurotransmitter receptor most of the time and the information contained in the frequency and the duration of trains of action potentials won't 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 presynaptic membranes contains 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 neural transmission by being released back into the synapse so these pumps are called reuptake pumps reuptake 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 in feet so the astrocytes in the central nervous system put their in feet 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 where sometimes the Aster site will actually transfer some of the substances of the neurotransmitters back into the axon terminal of the neuron where will be recycled and used again for neural transmission so all of these different methods allow the synapse to basically be rapidly turned on and off because 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