Question

Arrange the following in sequence during the transmission of nerve impulse at chemical synapse.
i. Neurotransmitter binds with receptors of post synaptic cell.
ii. Calcium channels open and the calcium diffuses inward from ECF.
iii. Impulse travels along the axon of presynaptic neuron.
iv. Release of neurotransmitter by exocytosis.
v. Synaptic vesicles fuse with cell membrane of axon terminal of presynaptic neuron.

• A. i, ii, v, iii, iv
• B. iii, v, ii, iv, i
• C. ii, v, i, iii, iv
• D. iii, ii, v, iv, i

Hint:

Sequence trick: Impulse $\rightarrow$ Ca$^{2+}$ entry $\rightarrow$ Vesicle fusion $\rightarrow$ Release $\rightarrow$ Binding

Answer 1

The Correct Option is D

Concept: Transmission of nerve impulse across a chemical synapse involves a sequence of electrical and chemical events.
• Electrical signal reaches axon terminal
• Triggers calcium influx
• Leads to neurotransmitter release
• Neurotransmitter binds to receptors on postsynaptic membrane

Step 1: Start with arrival of impulse.
The nerve impulse first travels along the axon of the presynaptic neuron. $\Rightarrow$ (iii)

Step 2: Opening of calcium channels.
Arrival of impulse opens voltage-gated calcium channels, allowing $\text{Ca}^{2+}$ to enter. $\Rightarrow$ (ii)

Step 3: Vesicle fusion.
Calcium influx triggers synaptic vesicles to fuse with the presynaptic membrane. $\Rightarrow$ (v)

Step 4: Release of neurotransmitter.
Neurotransmitters are released into synaptic cleft via exocytosis. $\Rightarrow$ (iv)

Step 5: Binding to receptors.
Neurotransmitters bind to receptors on the postsynaptic membrane. $\Rightarrow$ (i)

Step 6: Final sequence.
iii $\rightarrow$ ii $\rightarrow$ v $\rightarrow$ iv $\rightarrow$ i Final Answer: Option (D)