Overview Introduction The brainstem is composed of the midbrain, pons, and medulla Brainstem Structures Structure Cranial Nerves Comments Midbrain (Mesencephalon) Oculomotor nerve (CN III) Trochlear nerve (CN IV) Reticular activating system involved in arousal and alertness lesion can lead to coma Superior colliculus conjugate vertical gaze center Inferior colliculus auditory information processor Parinaud's syndrome due to compression of dorsal midbrain and pretectal area(e.g.,pinealoma, hydrocephalus) lesions the superior colliculus conjugate vertical gaze palsy Pons (Metencephalon) Trigeminal nerve (CN V) Abducens nerve (CN VI) Facial nerve (CN VII) Vestibulocochlear nerve (CN VIII) Medial longitudinal fasciculus lesion leads to intranuclear ophthalmoplegia (INO) Medulla (Myelencephalon) Glossopharyngeal nerve (CN IX) Vagus nerve (CN X) Hypoglossal nerve (CN XII) Vasomotor center Respiratory center Area postrema incomplete blood-brain barrier chemoreception of toxins triggers nausea and vomiting Medial lemniscus formed by decussating fibers of the nucleus gracillis and cuneatus Pyramids contain corticospinal tracts most decussate in the caudal medulla Olives send fibers through the inferior cerebellar peduncle distinguishing feature of medulla