Brainstem

The term brain stem (truncus encephali is a Latin synonym) refers to a composite substructure of the brain. It includes the midbrain, the pons and the medulla oblongata. Some authors include the cerebellum and/or parts of the diencephalon. A discussion of differences in the use of this term is presented in Anthoney (1994).

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 knob 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.

Function
The brain stem is the stalk of the brain below the cerebral hemispheres. It is the major route for communication between the forebrain, the spinal cord, and peripheral nerves. It controls various autonomic functions such as respiration and the regulation of heart rhythms as well as perceptual functions such as the primary aspects of sound localization.