In biology, depolarization is the event a cell undergoes when its membrane potential grows more positive with respect to the extracellular solution. Depolarization typically results from the influx of positively charged ions (such as sodium or calcium) into the cell. Alternatively, depolarization can also happen if potassium channels are closed. Compare to hyperpolarization. Depolarization of membrane potentials is important for other cell types, particularly muscle and nerve cells. Main article: Life There are many universal units and common processes that are fundamental to the known forms of life. ... Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ... Transmembrane potential difference is the electrical potential difference across a plasma membrane. ... An ion is an elementary particle or system of elementary particles with a net electric charge. ... General Name, Symbol, Number sodium, Na, 11 Series alkali metal Group, Period, Block 1 (IA), 3, s Density, Hardness 968 kg/m3, 0. ... General Name, Symbol, Number calcium, Ca, 20 Series alkaline earth metal Group, Period, Block 2 (IIA), 4, s Density, Hardness 1550 kg/m3, 1. ... In cell biology, potassium channels are the most common type of ion channel. ... Hyperpolarization has several meanings: In biology, hyperpolarization occurs when a cells membrane potential dips below its resting level. ... A top-down view of skeletal muscle Muscle is a contractile form of tissue. ... A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. ...

Literal definition

While the above definition is widely used by biologists, it is not correct in a literal sense. Literally, depolarization is any situation in which the membrane potential decreases in absolute value (i.e. approaches zero from either the positive or negative direction). Thus depolarization is not necessarily a change of voltage in a positive direction (inside the cell relative to outside), but rather any change in membrane potential that brings the voltage closer to a value of zero. For example, if a cell were to have a membrane potential of -80 mV and another were to have a membrane potential of +80 mV, both would literally be depolarizing if their membrane potentials moved toward -10 mV and +10 mV, respectively.

Despite its literal definition, biologists almost universally misuse the term to mean a change in membrane potential in the positive direction. This misuse arose because cells with positive resting potentials generally (if not entirely) do not exist in nature. Thus one never has a situation where a positive initial membrane potential becomes more negative. Given that, it is simply easier to equate depolarization with "positive change in membrane potential" and hyperpolarization with "negative change in membrane potential".

There are times in nature when the scietific vernacular does not make sense in terms of the literal definitions of depolarization and hyperpolarization. For example, during the initial falling phase of an action potential, the peak voltage of the action potential (approx. +30 to +40 mV) is moving toward 0 V. That is, during the initial part of the action potential falling phase, it is literally depolarizing (moving toward 0 V). Once the voltage passes through zero and continues to head toward resting potential, it is then literally hyperpolarizing. Nonetheless, in the vernacular the entire falling phase of the action potential is called a hyperpolarization or a repolarization (even though it is literally a depolarization following by a hyperpolarization). Schematic of an electrophysiological recording of an action potential showing the various phases which occur as the wave passes a point on a cell membrane. ...

Related topics

• membrane potential
• action potential