During the rising (depolarizing)phase of a neuronal action potential,
A)PK₊ becomes much greater than PNₐ₊.
B)PNₐ₊ becomes much greater than PK₊.
C)PK₊ is the same as PNₐ₊.
D)Na⁺ efflux (flow out of the cell)occurs.
E)K⁺ flows rapidly into the cell.

Question

During the rising (depolarizing)phase of a neuronal action potential,
A)PK₊ becomes much greater than PNₐ₊.
B)PNₐ₊ becomes much greater than PK₊.
C)PK₊ is the same as PNₐ₊.
D)Na⁺ efflux (flow out of the cell)occurs.
E)K⁺ flows rapidly into the cell.

Quizplus · Accepted Answer

During the rising (depolarizing) phase of a neuronal action potential, the membrane potential rapidly becomes less negative and more positive. This is primarily caused by the influx of sodium ions (Na⁺) into the cell, which leads to a rapid increase in the membrane potential. As a result, the concentration gradient of Na⁺ ions becomes strong, and the membrane potential becomes more positive. At the same time, potassium ions (K⁺) begin to move out of the cell down their concentration gradient, but this efflux occurs more slowly than the influx of Na⁺. Therefore, during the rising phase, the membrane potential is dominated by the influx of Na⁺, and PNₐ₊ becomes much greater than PK₊.

During the Rising (Depolarizing)phase of a Neuronal Action Potential