Depolarization of Neurons

[sugarbabee0]

Hey I'm having some trouble fully understanding chemical synapses. So i know that Ca rushes into the presynaptic neuron causing the neurotransmitters to be released. The neurotransmitters bind to the post synaptic receptors which open the voltage gated Na channels allowing Na into the neuron (depolarization of the post-synaptic neuron).

Now my questions are:
1)Does the neurotransmitter detach from the receptor when the cell is depolarized (when Na stops rushing in and K starts going out)?
2)Is the PREsynaptic cleft also de/polarized or have an action potential? Or is that term only used for the POSTsynaptic neuron?

Thank you in advance for your help

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[echolalia16]

The neurotransmitter should detach from the receptor, where it is broken down and/or reabsorbed into the presynapse. Otherwise you would get an endless stimulation, right? Or maybe I'm not understanding your question.
The presynaptic side of the cleft technically doesn't have action potentials, if I remember correctly. Action potentials are kind of puked from the axon into the terminal where they technically become graded potentials, but I think that is beyond the scope of the MCAT. I learned that in my neuro class, not my physiology class.

 

[sugarbabee0]

The neurotransmitter should detach from the receptor, where it is broken down and/or reabsorbed into the presynapse. Otherwise you would get an endless stimulation, right?

Right but is the neurotransmitter still attached while the postsynaptic is being re-polarized?

 

[echolalia16]

Right but is the neurotransmitter still attached while the postsynaptic is being re-polarized?

There might be a handful still hanging around but the interaction between the neurotransmitter and the postsynaptic receptors is very brief, and reuptake occurs pretty much immediately.
Your neurotransmitter in this case is catalyzing the flow of sodium which depolarizes the cell. The potassium channels are voltage gated which means once that threshold is hit, potassium is going to rush into the cell and repolarize it regardless of the sodium present (in fact, sodium is being pumped out of the cell at this point). Once this occurs, the neurotransmitter is essentially ineffective.
I don't think that the repolarization is causing the neurotranmitters to be removed. Many neurons can receive both excitatory and inhibitory responses from preneurons, thus it doesn't make sense if repolarization or depolarization cause neurotranmitter to fall off the receptor.