Final answer:
K+ does not flood out when Na+ channels open because K+ channels are voltage-gated with slower kinetics, leading to a delayed release of K+ ions. During the peak of an action potential, Na+ channels begin to close as K+ channels open, allowing for controlled repolarization and eventual hyperpolarization of the neuronal membrane.
Step-by-step explanation:
Why K+ Doesn't Flood Out When Na+ Channels Open
When Na+ channels open during the depolarization phase of an action potential, K+ does not flood out of the neuron because the potassium channels are voltage-gated and have different kinetics. While the Na+ channels open quickly upon reaching the threshold potential (-55 mV) and lead to a membrane potential of about +40 mV, the K+ channels open more slowly. The voltage-gated K+ channels are sensitive to a membrane voltage of -50 mV, but they do not have the same rapid response as Na+ channels.
At the peak of the action potential, the Na+ channels begin to close as the K+ channels open. This allows K+ to leave the cell while preventing an immediate flood of potassium ions. The delayed opening of K+ channels coincides with the inactivation of Na+ channels. As a result, during repolarization, K+ ions leaving the neuron cause the membrane potential to become more negative, ultimately leading to hyperpolarization. After hyperpolarization, K+ channels close with a delay, allowing the membrane to return to the resting potential, facilitated by the non-gated channels and Na+/K+ pump.