brain, spinal cord, and nerve disorders
Brain
Brain stem
The brain stem connects the cerebrum with the spinal cord. It contains a system of nerve cells and fibers (called the reticular activating system) located deep within the upper part of the brain stem. The reticular activating system controls levels of consciousness and alertness. The brain stem also contains many of the nerve center collections that control movements of the eyes, face, jaw, and tongue, including chewing and swallowing. The brain stem also automatically regulates critical body functions, such as breathing, blood pressure, and heartbeat, and it helps adjust posture and balance. If the entire brain stem becomes severely damaged, consciousness is lost, and these automatic body functions cease. That is, all brain activity is lost. This loss is considered Brain Death . Death soon follows. However, if the brain stem remains intact, the body may remain alive, even when severe damage to the cerebrum makes awareness, thought, and movement impossible. 