In the described patient with unilateral facial droop and an inability to move the forehead, which cranial nerve is affected?

• A. Trigeminal nerve (CN V)
• B. Vagus nerve (CN X)
• C. Facial nerve (CN VII)
• D. Hypoglossal nerve (CN XII)

Answer: (C)

The muscles that move the forehead, like the frontalis, are controlled by the facial nerve (cranial nerve VII). When this nerve is damaged on one side, you get ipsilateral facial weakness including an inability to raise the eyebrow or wrinkle the forehead on that side. This pattern points to a facial nerve palsy.

Other nerves don’t innervate the forehead’s expression muscles: the trigeminal nerve mainly handles muscles of mastication and facial sensation; the vagus nerve controls muscles of the pharynx and larynx; the hypoglossal nerve moves the tongue. Also, a true upper motor neuron lesion often spares forehead movement because its innervation to the forehead is bilateral, whereas a lower motor neuron lesion of the facial nerve directly disrupts the ability to move the forehead.