Practice question · Put in order
Put the events of chemical synaptic transmission in causal order.
- An action potential arrives at the presynaptic terminal button.
- Synaptic vesicles fuse with the membrane and release neurotransmitter into the cleft.
- Neurotransmitter diffuses across the cleft and binds postsynaptic receptors.
- Reuptake or enzymatic degradation clears the neurotransmitter from the cleft.
- Voltage-gated Ca2+ channels open and Ca2+ flows into the terminal.
Hints
- Something must TRIGGER vesicle release before the vesicles can fuse - which ion is it?
- Clearance comes last, only after the signal has already been passed to the next cell.
Show the answer
- An action potential arrives at the presynaptic terminal button.
- Voltage-gated Ca2+ channels open and Ca2+ flows into the terminal.
- Synaptic vesicles fuse with the membrane and release neurotransmitter into the cleft.
- Neurotransmitter diffuses across the cleft and binds postsynaptic receptors.
- Reuptake or enzymatic degradation clears the neurotransmitter from the cleft.
Why
The arriving spike opens Ca2+ channels; Ca2+ influx is the trigger that makes vesicles fuse and release transmitter, which then diffuses, binds receptors, and is finally cleared. Forgetting that calcium is the trigger is the most common slip here.
Practise Synaptic Transmission
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