In a cranial nerve motor examination, which nerve cannot be assessed for a motor component?

• A. Trochlear
• B. Trigeminal
• C. Facial
• D. Vestibulocochlear

Answer: (D)

The key idea is that not all cranial nerves have motor fibers. The vestibulocochlear nerve is purely sensory, carrying hearing and balance information through its cochlear and vestibular parts. It has no motor component to test, so you don’t evaluate its strength or movement in a motor exam. If you need to assess its function, you test sensory abilities such as hearing (audiometry, Weber/Rinne) and balance/vestibular function (head thrust, caloric testing, Romberg).

In contrast, the trochlear, trigeminal, and facial nerves all have motor components you can assess. The troclear nerve innervates the superior oblique muscle, so you test eye movements to look down and inward. The trigeminal nerve has motor fibers to the muscles of mastication, so you check jaw strength and jaw opening against resistance. The facial nerve innervates muscles of facial expression, so you observe symmetry and strength of smiling, frowning, and other facial movements.