Question

Which one of the following is the correct sequence of events that follows in a synaptic transmission of nerve impulse?

1. The presynaptic membrane is depolarized.

2. Voltage gated calcium channels open

3. Release of synaptic Vesicles

4. Calcium enters the synaptic knob

5. The neurotransmitter diffuses across the synaptic cleft and binds to the receptor proteins on the postsynaptic membrane.

• A. 2,1,4,3
• B. 3,2,4,1
• C. 1,2,3,4
• D. 4,1,3,2

Answer 1

The correct option is C

1,2,3,4

1) When the action potential arrives at the axon terminals, the axonal membrane is depolarised.

2) Depolarisation of the axonal membrane causes opening of the voltage gated ${Ca}^{2+}$ channels present at the synapse.

3) Opening of these channels causes an influx of ${Ca}^{2+}$ into the presynaptic neuron. The influx of ${Ca}^{2+}$ into the cell causes the synaptic vesicles present at the presynaptic membrane to fuse with the membrane and release the neurotransmitter contained in the vesicle, into the synaptic cleft.

4) The neurotransmitter then diffuses across the synaptic cleft and binds to the receptors located on the postsynaptic membrane.