Depolarization

In biology, depolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell. Depolarization is essential to the function of many cells, communication between cells, and the overall physiology of an organism.

Most cells in higher organisms maintain an internal environment that is negatively charged relative to the cell's exterior. This difference in charge is called the cell's membrane potential. In the process of depolarization, the negative internal charge of the cell temporarily becomes more positive (less negative). This shift from a negative to a more positive membrane potential occurs during several processes, including an action potential. During an action potential, the depolarization is so large that the potential difference across the cell membrane briefly reverses polarity, with the inside of the cell becoming positively charged.

The change in charge typically occurs due to an influx of sodium ions into a cell, although it can be mediated by an influx of any kind of cation or efflux of any kind of anion. The opposite of a depolarization is called a hyperpolarization.

Usage of the term "depolarization" in biology differs from its use in physics. In physics it refers instead to situations in which any form of polarity changes to a value of zero.

The process of depolarization is entirely dependent upon the intrinsic electrical nature of most cells. When a cell is at rest, the cell maintains what is known as a resting potential. The resting potential generated by nearly all cells results in the interior of the cell having a negative charge compared to the exterior of the cell. To maintain this electrical imbalance, microscopic positively and negatively charged particles called ions are transported across the cell's plasma membrane. The transport of the ions across the plasma membrane is accomplished through several different types of transmembrane proteins embedded in the cell's plasma membrane that function as pathways for ions both into and out of the cell, such as ion channels, sodium potassium pumps, and voltage gated ion channels.

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