Two somatic eyelid reflexes in the albino rat

Eyelid responses to air puffs directed at the cornea of the rat are shown to result from the activation of two reflexes. A brief early component of the response results from stimulation of the eyelids, especially the eyelashes. The larger, later component is initiated by stimulation of the cornea. Branches of the trigeminal nerve comprising the afferent limbs of the two reflexes were identified in physiological experiments by selective denervation of the upper eyelid, the lower eyelid, or globe, and by anatomical procedures. Responses of single orbicularis oculi motoneurons, recorded from a dorsal group of cells in the facial nucleus, indicate that both reflexes are served, in part at least, by the same motoneurons. A pause of contraction in responses to air puffs when spontaneous activity is present suggests that orbicularis oculi has Golgi tendon organs. The early response of the eyelash reflex habituates and differs in this respect from the early component of the human orbicularis oculi reflex.