What is depolarization and what causes it?

Depolarization is a critical process in the functioning of excitable cells, such as neurons and muscle cells. It refers to the reversal of the cell membrane's electrical potential from its resting state, which is typically polarized (with the inside of the cell being more negatively charged than the outside). Depolarization occurs when there is an influx of positively charged ions, such as sodium (Na+), into the cell. This influx makes the inside of the cell more positively charged, reducing the difference in charge between the inside and outside of the cell membrane. The cause of depolarization is often the opening of voltage-gated sodium channels in the cell membrane. When a stimulus is applied to the cell, these channels open, allowing sodium ions to flow into the cell down their concentration gradient. This inward flow of sodium ions increases the concentration of positively charged cations inside the cell and causes depolarization, where the potential of the cell is higher than the cell's resting potential. Once the sodium channels close, typically at the peak of the action potential, potassium (K+) channels open, allowing potassium ions to flow out of the cell, which helps to repolarize the cell and return it to its resting state.

The inward flow of sodium ions increases the concentration of positively charged cations in the cell and causes depolarization, where the potential of the cell is higher than the cell's resting potential. The sodium channels close at the peak of the action potential, while potassium continues to leave the cell.