Question

You notice a patient that has a broad palpebral fissure because his orbicularis oculi is weak (he can't close that eye). What CN controls this muscle?

Answer 1

The orbicularis oculi muscle, which is weak in the described patient, is controlled by the facial nerve, the seventh cranial nerve (CN VII), not by the oculomotor, trochlear, or abducens nerves which control other extraocular muscles.

Step-by-step explanation:

The patient's inability to close their eye, which is causing a broad palpebral fissure, can be attributed to a weakness in the orbicularis oculi muscle. This muscle is responsible for blinking and closing the eyes, and is controlled by the facial nerve, also known as the seventh cranial nerve (CN VII). The facial nerve is crucial for the muscles of facial expression, as well as for other functions such as taste sensation for the anterior two-thirds of the tongue and lacrimal and salivary gland stimulation.



While the oculomotor, trochlear, and abducens nerves (CN III, IV, and VI respectively) are responsible for controlling extraocular muscles that move the eyeball itself, the facial nerve is responsible for controlling most of the muscles of facial expression, including the orbicularis oculi.