Final answer:
Voltage-gated sodium channels have three conformations: closed, open, and inactive, facilitating the different phases of an action potential in nerve cells.
Step-by-step explanation:
The voltage-gated sodium channel can exist in three different conformations: closed, open, and inactive. These conformations regulate ion flow and are crucial for action potentials in nerve cells. Initially, the activation gate is closed preventing sodium entry, but upon reaching the threshold potential of approximately -55 mV, the activation gate opens and allows sodium ions to flow into the cell. This rapid influx of sodium leads to depolarization. Shortly thereafter, the inactivation gate closes, halting the sodium entry, which is essential for the repolarization phase of an action potential. Finally, the channel returns to the closed state with the inactivation gate open, ready for the next action potential.