Hyperpolarization

Hyperpolarization has several meanings:

• In biology, hyperpolarization occurs when a cell's membrane potential dips below its resting level.
  • While the undershoot of an action potential is called a hyperpolarization, this definition is to narrow. More broadly, the hyperpolarization of a biological cell means any change in trans-membrane voltage that is more polarized. Thus, hyperpolarizations can be in either the positive or negative direction. In the scientific vernacular however, a hyperpolarization is generally used (technically incorrectly) to describe any movement of membrane potential in a direction that makes it less positive or more negative. (See the article depolarization for a more complete explanation of the (mis)use of this nomenclature).

• In physics, hyperpolarization is the selective polarization of nuclear spin in atoms far beyond normal thermal equilibrium.