The brain stem is located at the base of the brain, in front of the cerebellum.  Through it travel all information signals from the remainder of the brain to the body, and vice versa.  In fact, the lowest  portion of the brainstem, known as the medulla, merges with the top of the cervical spinal cord.  In addition, the brainstem contains many centers or nuclei, which supply the cranial nerves (these nerves travel face and head), and the brainstem  is also  responsible for such vital functions as keeping us awake versus in a coma, breathing and other basic "housekeeping" functions of the body. 

From top to bottom, the brainstem may be divided into several segments:  the midbrain, the pons and the medulla.  Situated within the substance of the brainstem are the cranial nerve nuclei.