In the upper pons, which nucleus can be observed besides the trigeminal motor nucleus?

• A. Principal sensory nucleus of CN V (sensation from face)
• B. Inferior olivary nucleus
• C. Vestibular nucleus
• D. Dorsal motor nucleus of X

Answer: (A)

In the upper pons, the trigeminal nerve has two main components you can observe together: the motor nucleus and a primary sensory nucleus. The principal (chief) sensory nucleus of the trigeminal nerve sits in the pontine tegmentum, right near the trigeminal motor nucleus, and it processes discriminative touch and proprioception from the face. That proximity and location in the upper pons is why it’s the nucleus you’d notice besides the trigeminal motor nucleus on a cross-section.

The other nuclei listed aren’t located in the same upper-pontine region: the inferior olivary nucleus is in the medulla, the dorsal motor nucleus of X is in the medulla, and the vestibular nuclei lie more caudally at the pontomedullary junction and dorsal brainstem. Hence, the nucleus that fits the upper pons position and relation to the trigeminal motor nucleus is the principal sensory nucleus of CN V.