impulse

[im´puls]

1. a sudden pushing force.

2. a sudden uncontrollable determination to act.

cardiac impulse a heartbeat palpated over the left side of the chest at the apex of the heart. See also point of maximal impulse.

impulse control disorders a group of mental disorders characterized by repeated failure to resist an impulse to perform some act harmful to oneself or to others. In spite of the act's being socially unacceptable or inconsistent with the rest of the person's personality or lifestyle, he or she feels pleasure or emotional release upon doing it. Disorders in this category include intermittent explosive disorder, kleptomania, pathological gambling, pyromania, and trichotillomania.

nerve impulse the electrochemical process propagated along nerve fibers.

nerve impulse

A wave of physical and chemical excitation along a nerve fiber in response to a stimulus, accompanied by a transient change in electric potential in the membrane of the fiber.

nerve impulse

The wave-like progression of electrical depolarization that passes along a stimulated nerve fibre. The nerve impulse results from a movement of positive and negative ions across the membrane of the fibre.

Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

nerve impulse

the message conducted along the AXON of a NERVE (1). The impulse is a propagated negative charge on the outside of the membrane which results from a wave of DEPOLORIZATION passing along an axon. The RESTING POTENTIAL is reversed and becomes an ACTION POTENTIAL, and this passes down the axon at between 1 and 100 ms, depending on the diameter of the fibre, the presence of a MYELIN SHEATH, temperature, species of animal etc. Once an impulse is initiated it progresses without degeneration, and the strength or nature of the stimulus does not affect it; it either is generated or it is not (ALLORNONE LAW). Varying stimuli produce varying numbers of impulses (see SUMMATION). After each impulse there is a REFRACTORY PERIOD during which a second impulse may not pass.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

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References in periodicals archive

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