Abstract The electrical activity of the extraocular muscles in man has been studied by means of monopolar needle electrodes inserted into the muscles. The present investigation has been concerned mainly with the levator palpebrae superioris and the external and internal recti muscles. 1. 1. The levator palpebrae superioris muscle exhibits intense activity when the eyes look straight ahead. Lowering of the lid is accompanied by a decrease of the activity. Relaxation is complete when the eyes are closed or in the position of extreme downward gaze. Abrupt inhibition of all activity in the levator occurs at the beginning of a blink, regardless of the position of the lid. The inhibition appears to precede and outlast the reciprocal contraction of the orbicularis oculi. 2. 2. The recti muscles exhibit rather strong, persistent activity in all positions of the eye within the range normally used. This implies then that positioning is achieved by balanced maintained action of all the muscles taking part in the movement of the eye. This steady activity, though not dependent on the act of fixation since it persists in the dark, would however seem to be associated with the waking state. Each change of ocular fixation is accompanied by a gradual increase of the activity in the agonist and a corresponding decrease in the antagonist. The same is true for slow continuous movement. Nevertheless, in extreme positions of the gaze a minimal activity in the antagonist is more often than not observed. Rapid movements of the eye during quick changes in fixation between two points produce a brief acceleration of the activity in the agonist and complete inhibition of the antagonist.
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