Which rapid ionic event underlies the steep depolarization phase (phase 0) of a neuronal action potential?
Answer and explanation
Correct answer: B. Massive influx of Na+ through opened voltage-gated sodium channels
Once the membrane depolarizes to threshold (~ -55 mV), activation gates of voltage-gated Na+ channels snap open, permitting rapid inward Na+ flux down its steep electrochemical gradient toward its equilibrium potential (+60 mV).
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