1. Generally, any initial change, in response to a sudden step change in some factor, that is greater than the steady-state response to the new level of that factor; common in systems in which inertia or a time lag in negative feedback outweighs any damping that may be present. Changes in a negative direction are sometimes distinguished by the term undershoot, and the two may alternate in an oscillatory fashion, as in the transient oscillations of a pendulum when released from an initial displacement. 2. Momentary reversal of the membrane potential of a cell (inside becoming positive rather than negative relative to the outside) during an action potential; considered a form of o. (1) because, before discovery of o. (2), excitation was thought merely to depolarize the membrane to zero transmembrane potential.
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over·shoot 'ō-vər-.shüt n a rapid change in electrical potential and reversal of polarity that occurs during an action potential when a cell or tissue is stimulated
Medical dictionary. 2011.