The Brainstem

Abstract

The brainstem is best viewed when separated from the overlying cerebral hemispheres and cerebellum, and in a midsagittal section of the brain (Figs. 1–3; Chapter 2, Figs. 5–9). The brainstem is continuous with the spinal cord at the foramen magnum of the occipital bone and with the diencephalon at the incisura of the tentorium and the posterior clinoid processes of the sphenoid bone. It consists of the midbrain, pons, and medulla, which lie in close relationship to the cranial surface of the base of the occipital bone. The vertebral and basilar arteries lie between the ventral surface of the brainstem and the occipital bone (Chapter 2, Fig. 13). The paired cranial nerves originate or terminate in the brainstem, except for the olfactory, optic, and spinal portion of the accessory nerve (Fig. 1; Chapter 2, Figs. 5–9). The cerebellum lies posterior to the brainstem and is attached by three pairs of fiber bundles: the inferior, middle, and superior cerebellar peduncles (Fig. 2). The brainstem, cerebellum, roots of the cranial nerves, and vertebro-basilar arterial system are located in the posterior cranial fossa or infratentorial space (Chapter 2, Fig. 4).