Which main sensory relay nucleus of the trigeminal nerve is located in the medulla and responsible for sensory information of the ipsilateral face?

• A. Spinal nucleus
• B. Main sensory nucleus
• C. Mesencephalic nucleus
• D. Nucleus ambiguus

Answer: (A)

Pain and temperature sensation from the face travels through the spinal tract of the trigeminal nerve to the spinal trigeminal nucleus, which resides in the medulla and continues into the upper cervical cord. This spinal trigeminal nucleus acts as the sensory relay for those modalities on the same side of the face. The main (principal) sensory nucleus, by contrast, is located in the pons and handles discriminative touch and vibration. The mesencephalic nucleus sits in the midbrain and deals with proprioception from the jaw muscles, while the nucleus ambiguus is a motor nucleus for certain cranial nerves. So, the medullary spinal trigeminal nucleus is the correct match for relaying ipsilateral facial pain and temperature.