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(also nictitation), a protective unconditioned reflex (or a conditioned reflex formed on its basis) in response to stimulation of the sensory branches of the trigeminal nerve in the cornea or conjunctiva of the eye, in the skin of the eyelids, and in the eyelashes, as well as in response to light stimulation. The closing of the palpebral fissure before entry of a harmful agent into the eye is an important biological adaptation. During winking the eyeball is washed by lacrimal fluid, which helps remove foreign bodies. Winking is effected primarily by contraction of the orbital muscle, which is innervated by fibers of the facial nerve. In response to stimulation of the trigeminal nerve, the reflex arc is closed in the region of the medulla oblongata. Absence of winking is observed when the facial nerve is paralyzed or when the trigeminal nerve is damaged. Intensification and increase in the frequency of winking, often accompanied by tearing and photophobia, are observed with conjunctivitis.