Question

Create a numbered sequence of the events that comprise the action at a chemical synapse. Begin with the arrival of the impulse at the presynaptic membrane and finish with the creation of an EPSP and return to pre-event conditions.

Answer 1

1. Synthesis and storage of neurotransmitter in the vesicles.

2. Action potential reaches the presynaptic terminal.

3.Action potential depolarises the terminal and causes opening of calcium channels and release of calcium ions into the terminal.

4. Calcium binds with the special protein molecules called release sites in the presynaptic membrane.

5.Binding in turn causes the release sites to open through the membrane, allowing a few transmitter vesicles to release their transmitter into the cleft.

6. Neurotransmitter binds to receptors in the post synaptic membrane.

7. Opening and closing of the ion channels.

8.  Opening of sodium channels to allow large numbers of positive electrical charges to flow to the interior
of the postsynaptic cell causing excitation, or it can be opening of chloride ion channels through the postsynaptic
neuronal membrane causing inhibition.

9. Vesicles that store and release small-molecule transmitters are then continually recycled and used over and over
again.