The brainstem is the most primitive part of the brain and begins with the stem itself, but is also composed of the medulla oblongata, the pons, and the midbrain, from caudal to cranial on the ventral side of the brain. It supports basic subconcious functions of the body including heart, repsiration, and blood vessel diameter, swallowing, and vomiting.

Here the parts of the brainstem are labeled