Four cranial nerves emerge from the pons. Cranial nerves VI, VII, and VIII emerge from the pon-tomedullary junction. The facial nerve is located medial to the vestibulocochlear nerve. The abducens nerve (CN VI) emerges near the midline lateral to the corticospinal tract. The trigeminal nerve (CN V) emerges from the middle of the pons.
The midbrain (mesencephalon) is located between the pons and diencephalon. The cerebral aqueduct, a narrow channel that connects the third and fourth ventricles, passes through the midbrain. The inferior colliculi and superior colliculi are found on the dorsal aspect of the midbrain above the cerebral aqueduct. The inferior colliculus processes auditory information received bilaterally from the cochlear nuclei by axon fibers of the lateral lemniscus. The superior colliculi help direct movements of both eyes in gaze. The pretectal region is located just beneath the superior colliculi and in front of the oculomotor complex. This area contains interneurons involved in the pupillary light reflex. The massive cerebral peduncles extend ven-trally from the midbrain. The cerebral peduncles contain corticospinal and corticobulbar fibers. The interpeduncular fossa is the space between the cerebral peduncles.
The substantia nigra is the largest nucleus of the midbrain. It appears black to dark brown in the freshly cut brain because nigral cells contain melanin pigments. Neurons in the substantia nigra utilize Dopamine and GABA as neurotransmitters.
The medial lemniscus and spinothalamic tract and descending hypothalamic fibers course together ventrolateral to the periaqueductal gray.
The MLF continues to be located near the midline, just beneath the cerebral aqueduct. The mesencephalic nuclei of the trigeminal nerve are located on either side of the central gray.
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