Concept: This question tests your understanding of nerve impulse transmission, specifically the terminology used to describe the electrical changes across a neuron's membrane during signal propagation.

Why (A) is correct: When a nerve fibre is stimulated and depolarizes, the rapid change in membrane potential from negative to positive, followed by repolarization, is collectively known as an action potential. This is the electrical signal that travels along the neuron.

Why other options are wrong:

• (B) Spike Potential: While the rising phase of an action potential is sometimes referred to as a 'spike', the entire potential difference developed during depolarization and repolarization is the action potential.
• (C) Reaction Potential: This is not a standard biological term for nerve impulse.
• (D) None of these: Option A is correct.

Common Mistake: Students sometimes confuse resting potential (the potential when the neuron is inactive) with action potential (the potential during impulse transmission).

NEET Tip / Mnemonic: Remember the sequence: Resting → Depolarization → Repolarization → Hyperpolarization. The 'D' phase is where the action potential is generated.

Correct Answer: (A)