The brainstem projects from the center of the underside of the brain. This elongated structure connects the upper areas of the brain to the spinal cord. Evolutionarily, the brainstem is one of the oldest parts of the brain. It is responsible for consciousness, sleep, attention, respiration, blood pressure, coordination of eye movement, and control of the heart. The brainstem relays all nerve signals to and from the brain. Three structures comprise the brainstem: the midbrain, pons and medulla oblongata.
Midbrain
The midbrain is the uppermost part of the brainstem. Midbrain functions include the capacity for consciousness and visual and auditory reflexes. The midbrain contains the cerebral peduncle, which contains the nerves necessary for voluntary movement. Two other small midbrain structures--the red nucleus and the substantia nigra--also play a role in the coordination of voluntary movement. The substantia nigra is the primary brain area affected by Parkinson's disease.
Pons
The pons is between the midbrain and the medulla oblongata of the brainstem. Pons functions include relay of signals to control voluntary movement, sensory perceptions and posture; sleep pattern control; and facial and eye movement control. A stroke at the base of the pons often causes a devastating condition called locked in syndrome. All muscle function is lost--except for eye movement, which is spared. Consciousness and mental functions remain intact, but the patient is unable to move or communicate other than through eye movements.
Medulla Oblongata
The medulla oblongata is a critically important structure connecting all other areas of the brain with the spinal cord. In addition, this part of the brainstem contains the life-sustaining control centers for the lungs and heart. The control centers for coughing, swallowing, gagging and vomiting are also located in the medulla oblongata. Because it carries all messages to and from the brain and controls heart and lung function, the medulla oblongata is often considered the most vital part of the brain.
