What occurs during the depolarization phase of a nerve cell?

During the depolarization phase of a nerve cell, the primary event is the influx of sodium ions into the cell. This process is a crucial step in generating an action potential, which is essential for the transmission of nerve impulses.

When a nerve cell is at rest, the interior of the cell is negatively charged compared to the outside, primarily due to the distribution of ions across the membrane, with sodium ions being more concentrated outside the cell and potassium ions inside. Upon stimulation, voltage-gated sodium channels open, allowing sodium ions to rush into the cell. This influx of positively charged sodium ions causes the interior of the cell to become less negative, leading to depolarization.

Depolarization is key to the propagation of electrical signals along the nerve fibers, as it changes the electrical state of the membrane enough to trigger additional channels to open further down the neuron, continuing the signal transmission.

The other options do not accurately reflect the events of depolarization. The efflux of potassium ions typically occurs during repolarization, when the cell returns to its resting state. Chloride and calcium ions do not play a primary role in the depolarization phase in the context of action potentials in the same way that sodium does. Thus, the emphasis on sodium