alleryThe rapid depolarisation phase of an action potential is caused by
AK⁺ flowing out of the cell
BNa⁺ rushing into the cell through voltage-gated channels
CCl⁻ flowing into the cell
Dactive pumping of Na⁺ out
Answer & Solution
Correct answer: B. Na⁺ rushing into the cell through voltage-gated channels
Voltage-gated Na⁺ channels open when the membrane is depolarised to threshold.
Na⁺ floods in, driving the membrane potential to about +30 mV — the upstroke of the action potential.
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