By Renée Grinnell

Rhythmic, unintentional, rapidly alternating flexion and extension of opposing muscles in one or more parts of the body, often the hand or jaw.

Example: A teacher’s extended right hand shakes. Her writing has become illegible, and her symptoms worsen when she drinks coffee.

    Last reviewed: By John M. Grohol, Psy.D. on 12 Nov 2008