Mostly enveloped by the cerebrum and cerebellum (blue), the visible part of brainstem is shown in black. Viewed from the right.
The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. The upper segment of the human brain stem, the pons, contains nerve fibers that connect the two halves of the cerebellum. It is vital in coordinating movements involving right and left sides of the body. Below the pons and continuous with the spinal cord is the medulla, which transmits ascending and descending nerve fibers between the spinal cord and the brain. The medulla also directly controls many involuntary muscular and glandular activities, including breathing, heart contraction, artery dilation, salivation, vomiting, and probably laughing. The nuclei of some of the nerves that originate in the brain are also located in the brain stem. Nerve fibers in the brain stem do not readily regenerate, hence injury may result in permanent loss of function. See also nervous system.
The lower part of the brain stem is the medulla oblongata, grossly comprising the medullary pyramids and the olivary bodies or olives. The pons is a structure above the medulla. The reticular activating system is situated in between the medulla and metencephalon, and is considered to be at the "core."
Differentiation of the brain stem from the cerebrum is complex, both anatomically and taxonomically. Some taxonomies describe the brain stem as the medulla and mesencephalon while others include diencephalic regions.
The adult human brainstem emerges from parts of all three vesicles in the neural tube.
Anthoney, Terence (1994). Neuroanatomy and the Neurologic Exam: A Thesaurus of Synonyms, Similar-Sounding Non-Synonyms, and Terms of Variable Meaning, Boca Raton, Florida: CRC-Press. ISBN 0849386314.
