During depolarization of a cell, what is the primary change happening?

During depolarization of a cell, the primary change that occurs is an influx of sodium ions, which leads to a decrease in the negative charge inside the cell, resulting in a more positive internal environment. This process begins when the cell membrane reaches a certain threshold, stimulating voltage-gated sodium channels to open. As sodium ions rapidly flow into the cell, the interior, which was previously at a resting negative potential, becomes less negative and eventually more positive. This shift in electrical charge is crucial for the propagation of action potentials in neurons and muscle cells, enabling communication and function.

The other options do not accurately describe the process occurring during depolarization. For instance, suggesting that the cell is less permeable to sodium ions contradicts the very mechanism of depolarization, as it is characterized by increased sodium permeability. Similarly, stating that the inside of the cell becomes more negative or that the cell membrane becomes highly permeable to potassium ions would describe different physiological events that occur during repolarization or resting states rather than the depolarization phase.