Review Question - QID 106262

The gentleman in the question stem has sustained an injury to the mandibular branch of the trigeminal nerve (CN V3). It is the only branch of the trigeminal nerve that has both motor and sensory components.

The trigeminal nerve (CNV) is primarily responsible for the majority of the sensory innervation of the face, with the exception of the mandibular branch, which innervates the four muscles of mastication among others. This branch is comprised of both sensory (afferent) and motor (efferent) components. Injury to the peripheral nerve can result in unilateral paralysis, in which jaw deviation occurs toward the open paralyzed side, which results from the action of normal pterygoids on the opposite side.

Speiker describes the well-integrated role of CNV in mastication and its cerebellar control center. He reports that the muscles of mastication work in a coordinated fashion to mix the food bolus with saliva and propel it from the anterior oral cavity into the oropharynyx, where the involuntary swallowing reflex is triggered. The cerebellum controls output for the motor nuclei of cranial nerves V, VII and XII. The entire sequence lasts about one second.

Dumitru and Wasserburger suggest that in patients complaining of facial sensory dysfunction, malocclusion, or weakness of the muscles of mastication after mandibular fracture, an electrophysiologic examination can assist in evaluating cranial nerve integrity.

Illustration A shows the anatomy of the trigeminal nerve and its respective branches.
Illustration B shows an MRI of the trigeminal nerve with a comparison between normal location and contralateral displacement secondary to tumor growth.

Incorrect Responses:
Answers 1-2: The mandibular branch of the trigeminal nerve has both motor and sensory components.
Answers 4-5: The mandibular branch of the trigeminal nerve does not include sympathetic or parasympathetic branches.