The outside of a neuron is positively charged at resting potential. Why do K+ ions leave the cell when K+ channels open during an action potential?
A. Negatively charged proteins leave the cell at the onset of the action potential.
B. The diffusion gradient is the only factor that affects ion movement.
C. K+ ions are actively pumped out by the sodium-potassium pump acting in reverse.
D. Voltage-gated K+ channels open when membrane potential reaches +50 mV during the depolarization phase. The diffusion gradient and electrical force cooperate to drive K+ ions out of the cell.
Answer: D
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