Myoclonic activity in a patient with inherited essential myoclonus illustrating widespread activation of many muscles. A is a spontaneous jerk which occurred at rest, in which the cranial nerves and both arms were activated. B is a jerk evoked by attempted right wrist flexion in which the cranial nerves and left arm were activated. Voltage calibration is, for A, 0.05 mV for orbicularis oculi and 0.2 mV for the other muscles and, for B, 0.5 mV for APB and 1 mV for other muscles. Time calibration is 100 ms. Orbicularis oculi (OO), Masseter (M), sternomastoid (S), finger flexors (FF), biceps (B). Right (R), left (L).