During phase 0 of action potential, the cell experiences a rapid increase in which ion?

During phase 0 of the action potential, the cell experiences a rapid increase in sodium ions. This phase is characterized by the depolarization of the cell membrane, which occurs when voltage-gated sodium channels open in response to a stimulus. As sodium ions flow into the cell, the interior becomes more positive compared to the outside, leading to a rapid upswing in the membrane potential. This influx of sodium ions is crucial for initiating the action potential and allowing the electrical signal to propagate along the cell.

Other ions, such as calcium and potassium, play significant roles at different phases of the action potential, but during phase 0, it is specifically the sodium ions that increase rapidly, facilitating this critical depolarization phase. Chloride ions also have a different role in neuronal excitability and are not primarily associated with phase 0 of the action potential. Thus, focusing on sodium is key to understanding the mechanics of the action potential's initial phase.