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?

A. Trigeminal nerve (CN V)
B. Facial nerve (CN VII)
C. Glossopharyngeal nerve (CN IX)
D. Hypoglossal nerve (CN XII)

Answer 1

The Facial nerve (CN VII) controls the orbicularis oculi muscle, which is responsible for closing the eyelids. Weakness in this muscle suggests facial nerve dysfunction, and testing muscle strength can assess its function.

Step-by-step explanation:

The Facial nerve (CN VII) is responsible for controlling the orbicularis oculi muscle, which allows for eyelid closure. When someone has a broad palpebral fissure due to weak orbicularis oculi, it is indicative of facial nerve dysfunction. The strength of this muscle can be tested by having the patient attempt to squeeze their eyes shut while the examiner tries to pry them open. This test is not only for observing muscle contraction but to assess the function of the facial nerve for any asymmetry or weakness, which is why the examiner may ask for a second attempt to verify the consistency of muscle contraction