North American Veterinary Licensing Examination (NAVLE) Practice Test

The cranial nerve that mediates the closure of the eyes is the seventh cranial nerve, known as the facial nerve. This nerve is responsible for the motor control of the muscles of facial expression, which includes the orbicularis oculi muscle that is essential for closing the eyelids.

When this nerve is stimulated, it allows for the contraction of the orbicularis oculi, facilitating the blinking reflex and voluntary closure of the eyes. Dysfunction of the facial nerve can result in problems such as inability to close the eyelids properly, which can lead to further complications like exposure keratitis.

The other cranial nerves listed do not primarily operate the eyelid closure. The fifth cranial nerve, for example, is the trigeminal nerve and is primarily responsible for sensation in the face and motor functions such as biting and chewing. The third cranial nerve, the oculomotor nerve, controls most of the eye's movements and is involved in controlling the pupil but is not directly responsible for eyelid closure. The tenth cranial nerve, the vagus nerve, is primarily involved in autonomic functions of the body and has no direct role in eyelid movements. Thus, the role of the facial nerve in eyelid closure is