Reciprocal reflex activity in ocular muscles: implications in spontaneous blinking and Bell's phenomenon.

Levator palpebrae (m. lev. palp.) and rectus superior (m. rect. sup.) are two synergistic muscles in vertical gaze movements. However, they show an antagonistic behavior during electrically induced blink and glabellar reflexes. This can be considered as an easy and useful method for their differentiation in the electrophysiological study of certain oculopalpebral motor disorders. Blinking consists of a series of reflex activities, the most outstanding ones being an early m. lev. palp. basal activity inhibition, followed by the activation of the orbicularis oculi muscle and a brief increase in m. rect. sup. activity (reflex Bell phenomenon). This coordinated reflex organization could be perfectly related to that known in other human nociceptive reflexes.