Question

Choose the option that shows the correct sequence of the following steps involved in the generation and conduction of a nerve impulse.
I. The number of cations inside the axon increases.
II. Na+ ions diffuse into the neuron from the ECF.
III. Membrane potential changes from -70 mV to about +30 mV.
IV. Application of stimulus make membrane of nerve fibre more permeable to Na+.

• A. II \(\rightarrow\) I \(\rightarrow\) IV \(\rightarrow\) III
• B. IV \(\rightarrow\) II \(\rightarrow\) I \(\rightarrow\) III
• C. I \(\rightarrow\) II \(\rightarrow\) IV \(\rightarrow\) III
• D. III \(\rightarrow\) II \(\rightarrow\) I \(\rightarrow\) IV

Hint:

Start with the stimulus, then sodium entry, then build-up of positive charge, then reversal of potential.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
A nerve impulse is generated by a sudden change in the permeability of the axon membrane to sodium.

Step 2: Order of events
IV: a stimulus makes the membrane highly permeable to \(\text{Na}^{+}\).
II: \(\text{Na}^{+}\) ions diffuse in from the ECF.
I: positive ions accumulate inside the axon.
III: potential changes from \(-70\ \text{mV}\) to about \(+30\ \text{mV}\).

Step 3: Conclusion
The correct sequence is IV, II, I, III.

Final Answer:
The sequence is IV, II, I, III. \[ \boxed{\text{(B) }\text{IV}\rightarrow\text{II}\rightarrow\text{I}\rightarrow\text{III}} \]