Which cranial nerve is the only one with a dermatome?

The correct answer is the Trigeminal nerve. This cranial nerve is unique among the cranial nerves because it has a clear dermatome distribution. A dermatome is a specific area of skin that is mainly supplied by a single spinal nerve root. The Trigeminal nerve is divided into three main branches: the ophthalmic, maxillary, and mandibular branches, each being responsible for sensory innervation to different regions of the face. This sensory supply can be mapped, similar to how dermatomes from spinal nerves are mapped, which is why the Trigeminal nerve stands out in the context of dermatomes.

The other cranial nerves mentioned do not have this dermatome-like distribution. The Facial nerve primarily serves motor functions to the muscles of facial expression and has limited sensory components focused on taste. The Optic nerve is primarily responsible for vision with no sensory distribution to skin areas. The Hypoglossal nerve is focused on the motor control of the tongue without any sensory function. Thus, the Trigeminal nerve is distinctive for its role in providing sensory innervation in a manner akin to dermatomes.