How is eyelid movement initiated during voluntary winking?

During voluntary winking, both portions of the orbicularis oculi muscle—the orbital and palpebral portions—play crucial roles in the eyelid movement. The palpebral portion primarily functions to gently close the eyelids during blinking, while the orbital portion is responsible for forcefully closing the eyelids, such as during winking or when exposed to protective stimuli.

In the action of winking, the coordination between these two portions allows for both rapid and controlled eyelid movement. The levator palpebrae muscle, while important for elevating the upper eyelid during opening, does not actively facilitate the closing of the eyelids, which is essential in the winking motion. This collaborative action of both portions of the orbicularis oculi is what allows for a comprehensive and effective wink, highlighting their significance in this specific voluntary movement.