During the generation of a nerve impulse (action potential), which event is responsible for the rapid depolarization phase of the axonal membrane?

Answer and explanation

Correct answer: D. Rapid opening of voltage-gated Na+ channels causing a massive influx of Na+ into the axoplasm

  1. Step 1: When a threshold stimulus reaches an excitable membrane, voltage-gated sodium channels open rapidly.
  2. Step 2: Sodium ions () rush into the axoplasm down both their steep chemical concentration gradient and electrical gradient (electrochemical influx).
  3. Step 3: This massive inward movement of positive charge reverses the membrane polarity from -70 mV to approximately +30 mV, which constitutes the depolarization phase of the action potential.
Answer
Rapid opening of voltage-gated Na+ channels causing a massive influx of Na+ into the axoplasm
Why not the others: 'Rapid opening of voltage-gated K+ channels...' causes efflux, which is responsible for repolarization, not depolarization; 'Sudden activation of the Na+/K+ pump...' restores baseline ionic gradients over time but does not generate the action potential spike; 'Immediate closure of all ion channels...' would prevent any current flow.

Practise more Excretory Products, Locomotion and Movement, Neural Control.

Free questions with an explanation for every one, and full timed NEET UG mock tests.

All Excretory Products, Locomotion and Movement, Neural Control questionsTake a mock test

More Excretory Products, Locomotion and Movement, Neural Control questions