In human neurobiology, what ion influx through voltage-gated channels is primarily responsible for the rapid depolarization phase of an action potential?
Answer and explanation
Correct answer: A. Sodium ions
- Step 1: When a neuron's membrane potential reaches threshold (around -55 mV), voltage-gated sodium channels open rapidly. Step 2. Inward diffusion of Na+ ions down their electrochemical gradient causes rapid depolarization toward +30 mV. Answer: Sodium ions. Why not the others: Potassium efflux causes repolarization; chloride influx causes hyperpolarization (inhibition).
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