Question

During the ........... the negative membrane becomes less negative, reaches zero and then becomes positive.

• A. Hyperpolarizing phase
• B. Repolarizing phase
• C. Depolarizing phase
• D. Action potential
• E.

Hint:

Depolarization = Sodium influx. Repolarization = Potassium efflux. Hyperpolarization = Overshoot negativity.

Answer 1

The Correct Option is C

Step 1: Normal resting potential.
The resting membrane potential of a neuron is about -70 mV, maintained by sodium-potassium pumps and ion channels.
This means the inside of the cell is more negative compared to the outside.
Step 2: What happens during depolarization.
When a stimulus reaches threshold, voltage-gated sodium channels open.
Sodium ions rush inside the cell, causing the membrane potential to rise.
The inside of the cell becomes less negative, eventually reaching zero and then turning positive.
Step 3: Analysis of options.
- (A) Hyperpolarizing phase: This occurs after repolarization, when the membrane becomes more negative than the resting potential. Not correct here.
- (B) Repolarizing phase: During this phase, potassium ions move out of the cell, restoring the negative potential. Not correct.
- (C) Depolarizing phase: Correct. This is when the negative membrane becomes less negative, reaches zero, and becomes positive.
- (D) Action potential: The overall process includes depolarization, repolarization, and hyperpolarization. The specific phase asked is depolarization.
Step 4: Clinical correlation.
Depolarization is essential for nerve conduction and muscle contraction. Abnormal depolarization can cause arrhythmias, seizures, or muscle weakness.
Step 5: Conclusion.
Therefore, the depolarizing phase is the correct answer.