Medical Definition of impulse
1: a wave of excitation transmitted through tissues and especially nerve fibers and muscles that results in physiological activity or inhibition
2a: a sudden spontaneous inclination or incitement to some usually unpremeditated action <some uncontrollable impulse…may have driven the defendant to the commission of the murderous act—B. N. Cardozo>b: a propensity or natural tendency usually other than rational <the fundamental impulse of self-expression—Havelock Ellis>
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