Question

In fast response action potentials, Na+ conductance is at its highest during phase

A) Phase 0 (depolarization)
B) Phase 1 (early repolarization)
C) Phase 2 (plateau)
D) Phase 3 (repolarization)

Answer 1

Na+ conductance reaches its peak during Phase 0, which is the depolarization phase of an action potential.

Step-by-step explanation:

In fast response action potentials, Na+ conductance is at its highest during Phase 0 (depolarization). During this phase, the voltage-gated Na+ channels open in response to a stimulus reaching the threshold potential, allowing a rapid influx of Na+ ions into the cell. This surge of positive ions causes the membrane potential to rise sharply to around +30 mV. The rising phase of the action potential is brief, typically lasting between 3-5 milliseconds, after which the sodium channels close, and the cell undergoes subsequent phases including early repolarization, plateau, and repolarization.