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• 6th Abducens N-

• Abducens nucleus is in the pons under the medial eminence forming facial colliculus. The nerve projects ventral through the pons proper to exit through the pyramid at pons-medulla junction. Outside the brainstem the nerve passes over the belly of the pons as it goes to the lateral rectus M. in the orbit.

• 5th Trigeminal N-

• Motor nucleus is in line with the facial and ambiguus N. A smaller motor branch exits medially in the mid-pons between pons proper and the middle cerebellar peduncle. The motor branch serves the muscles of mastication and the tensor tympani muscle of the ear.
• Sensory neurons in Gasserion ganglion (semilunar) innervate the entire face and the head back to the ear and dorsal to the posterior crown. Central projections enter mid-pons and descend synapsing in pons, medulla in brainstem and to C4 in the cord. Rostral-caudal distribution in the brainstem to the cord is onion skin-like from the lips back on to the face to the ear. The 5th nerve branches, however, are opthalmic (upper), maxillary (middle) and mandibular (lower).
• The mesencephalic root is represented by electotonically coupled neurons as the only primary sensory neurons within the CNS. The mesencephalic nucleus lies along the sulcus limitans extending into the midbrain. One root goes to jaw sensory receptors and teeth receptors and the other root serves in reflex path to the motor nucleus of the 5th.