The Brainstem

Brainstem - The lower extension of the brain where it connects to the spinal cord. Neurological functions located in the brainstem include those necessary for survival (breathing, digestion, heart rate, blood pressure) and for arousal (being awake and alert).

Most of the cranial nerves come from the brainstem. The brainstem is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the highest parts of the brain.

The brainstem is a subcortical structure that lies at the top of the spinal cord. The brainstem is the site of entry into the brain for ten of the twelve cranial nerves, nerves that send signals to and from parts of the head and neck. The brainstem encompasses three neural centers: the medulla, pons, and midbrain. The medulla and the pons organize many complex and sustained reflexes. The postural reflexes help maintain posture and balance, and the vital reflexes mediate necessary internal functions such as breathing and heart rate. The midbrain controls basic movement patterns involved in feeding, grooming, and attacking. The neural centers of the midbrain also send signals to the spinal cord to control the speed of locomotion (walking or running). The midbrain and the pons work together to maintain or change patterns of sleep and arousal.

Although the brainstem is sufficient to produce a wide range of simple movements and behaviors, it cannot direct those behaviors in any meaningful way. An animal whose nervous system is severed completely just above the brainstem, eliminating any communication between the body and the rest of the brain, can still demonstrate almost all normal behaviors, including walking, running, eating, copulating, grooming, and attacking. Thus, we know that the brainstem is all that is needed to produce those behaviors. However, the animal does not direct those behaviors toward any particular goal or perform them spontaneously; it only reacts to immediate stimuli. For example, if placed on a treadmill, it will walk, but will not spontaneously walk toward an interesting object. Other, higher-up parts of the brain are necessary to produce spontaneous, goal-oriented behaviors.

• Medulla Oblongata -The medulla oblongata functions primarily as a relay station for the crossing of motor tracts between the spinal cord and the brain. It also contains the respiratory, vasomotor and cardiac centers, as well as many mechanisms for controlling reflex activities such as coughing, gagging, swallowing and vomiting.

• Midbrain - The midbrain serves as the nerve pathway of the cerebral hemispheres and contains auditory and visual reflex centers.

• Pons - The pons is a bridge-like structure which links different parts of the brain and serves as a relay station from the medulla to the higher cortical structures of the brain. It contains the respiratory center.