College of Massage Therapists of British Columbia (CMTBC) Practice Exam

What cranial nerve is unique for having a dermatome?

1. Glossopharyngeal

2. Trigeminal

3. Optic

4. Facial

The correct answer is: Trigeminal

The correct answer is the trigeminal nerve, which is unique among cranial nerves for having a dermatome. The trigeminal nerve is responsible for sensation in the face and has three main branches: the ophthalmic, maxillary, and mandibular. Each of these branches supplies specific areas of the face, creating distinct sensory territories, much like dermatomes associated with spinal nerves in the body. Dermatomes are regions of skin that are primarily supplied by a single spinal nerve root. While cranial nerves generally do not exhibit dermatome-like characteristics, the trigeminal nerve's division into three branches that innervate specific facial regions is a notable exception. This distinction helps in clinical evaluations and diagnoses related to sensory deficits in facial regions, as each branch can be assessed separately for function. Other cranial nerves listed do not function in this dermatome-like manner. The glossopharyngeal nerve is primarily involved in taste and sensation in the back of the throat and does not have a distinct dermatome pattern. The optic nerve is responsible for vision and does not have sensory territories related to skin. The facial nerve predominately controls muscles of facial expression and conveys taste sensations from the anterior two-thirds of the tongue, again lacking a dermatome