räpytysrefleksi

Räpytysrefleksi, also known as the blink reflex or corneal reflex, is an involuntary action that causes the eyelids to close. It is a protective mechanism designed to shield the eyes from potential harm. This reflex is triggered by a variety of stimuli, most notably touch or the threat of touch to the cornea, the transparent outer layer of the eye. Other stimuli that can elicit the räpytysrefleksi include loud noises, sudden bright lights, and even a puff of air directed towards the eye.

The räpytysrefleksi involves a complex neural pathway. When the cornea is stimulated, sensory receptors send signals via the trigeminal nerve (cranial nerve V) to the brainstem. Within the brainstem, specifically the pons and medulla oblongata, these signals are processed. Motor commands are then sent out through the facial nerve (cranial nerve VII), causing the orbicularis oculi muscles to contract, resulting in eyelid closure. This process happens very rapidly, typically within milliseconds.

There are two components to the blink reflex: a direct or ipsilateral response, where the eyelid on the stimulated side closes, and a consensual or contralateral response, where the eyelid on the opposite side also closes simultaneously. This coordinated action ensures comprehensive protection for both eyes. The räpytysrefleksi is a crucial component of ocular defense, preventing foreign bodies from entering the eye and maintaining corneal hydration by spreading tears. Its integrity is often tested as part of neurological examinations to assess the function of cranial nerves V and VII.