Occipitofrontalis muscle: functional analysis revealed by electromyography.

The occipital and frontal bellies of the right occipitofrontalis muscle were studied electromyographically in thirty volunteers in various movements, using a special steel electrode (80 microns diameter). The occipital and frontal bellies have independent actions despite the galea aponeurotica. The frontal belly initially raises the homolateral eyebrow, followed by a displacement of the galea aponeurotica, drawing the scalp forward; therefore it is active in the formation of the transversal wrinkling in the forehead. The occipital belly eventually can be active during raising of the eyebrown, nevertheless it does not interfere with the action of the frontal belly. The occipital belly alone is responsible for drawing back the galea aponeurotica. The occipital belly is also active during smiling and yawning, and can be active during the movements of the auricula.