The trigeminal motor nucleus is located in which portion of the brainstem?

• A. Upper pons
• B. Medulla
• C. Midbrain
• D. Spinal cord

Answer: (A)

The motor neurons that control the muscles of mastication reside in the trigeminal motor nucleus, which lies in the tegmentum of the upper portion of the pons. From this nucleus, axons exit with the motor root of the trigeminal nerve to innervate the jaw muscles (masseter, temporalis, medial and lateral pterygoids) as well as a few other muscles like tensor tympani and tensor veli palatini. Placing the nucleus in the upper pons fits the brainstem’s organization of cranial nerve nuclei, since other motor nuclei are located in different levels (the medulla houses nuclei for other nerves, the midbrain houses others, and the spinal cord contains no cranial nerve motor nuclei). So, the correct location is the upper part of the pons.