Final answer:
During the depolarization phase of an action potential, voltage-gated Na+ channels are open, allowing sodium ions to enter the neuron, while voltage-gated K+ channels remain closed until repolarization begins.
Step-by-step explanation:
Voltage-gated K+ channels are closed and voltage-gated Na+ channels are open during the depolarization stage of the action potential generation. For the action potential to develop, this time frame is essential. At a membrane potential threshold of about -55 mV, the voltage-gated Na+ channels open quickly. More depolarization results from the influx of sodium ions (Na+) into the neuron. These channels go through a brief inactivation period where they close soon after opening as the internal voltage rapidly increases to approximately +40 mV. Positive charge accumulates inside the neuron during this phase due to the voltage-gated K+ channels' continued closure.
Potassium ions (K+) can leave the cell through voltage-gated K+ channels that open shortly after the action potential peak, inactivating the Na+ channels. The K+ outflow marks the start of the repolarization stage. The Na+/K+ pump and the non-gated ion channels eventually cause the membrane potential to return to its resting state following a brief hyperpolarization.