Superiorly to inferiorly, the brainstem is composed of the diencephalon, midbrain, pons, and medulla oblongata. These structures are densely populated by nuclei and white matter tracts that allow communication among the cerebral hemispheres, cerebellum, and spinal cord. The major white matter tracts that travel through the brainstem are the reticular formation, pontocerebellar tract, corticospinal and corticobulbar motor tracts, spinothalamic tract, dorsal column/medial lemniscus, lateral lemniscus, trigeminal lemniscus, and spinotrigeminal tract.
The diencephalon flanks the third ventricle and contains the epithalamus, subthalamus, hypothalamus, and thalamus. Notable structures include the pineal gland, mammillary bodies, nucleus of Meynert, subthalamic nucleus, lateral geniculate nucleus, and medial geniculate nucleus. The diencephalon is involved in memory consolidation, sensory integration, modulation of motor activity, and regulation of consciousness.
The midbrain envelops the cerebral aqueduct connecting the third and fourth ventricles. Notable structures include the superior and inferior colliculi, medial longitudinal fasciculus, substantia nigra, red nucleus, dorsal raphe nucleus, periaqueductal grey, and the nuclei of cranial nerves (CNs) III and IV. The midbrain is involved in visual and auditory processing, oculomotor reflexes, coordination of eye movements, and motor regulation (substantia nigra, red nucleus).
The pons connects the midbrain with the medulla and cerebellum. Notable structures include the locus coeruleus, pontine nucleus, and the nuclei of CNs V, VI, VII, and VIII. The pontine structures are involved in coordination, autonomic functions, hearing, taste, facial sensation and motor function.
The medulla connects the pons to spinal cord and abuts the fourth ventricle. The nucleus solitarius, cardiovascular, respiratory, vomiting, and vasomotor centers contribute to the autonomic nervous system. The nucleus ambiguus and inferior salivary nucleus regulate swallowing. The gracile and cuneate nuclei, also known as the dorsal column nuclei, integrate sensory input from the dorsal column-medial lemniscus pathway. The medullary pyramids carry motor fibers of the corticobulbar and corticospinal tracts. The olivary bodies and vestibular nucleus regulate coordination and equilibrium. The nuclei of CNs IX, X, XI, and XII are located in the medulla.
Chin Clin Oncol. 2022;11(2):15 © 2022 AME Publishing Company