Brain Stem
The medulla oblongata, pons, midbrain and diencephalon constitute the brain stem. The brain stem connects the spinal cord to the remainder of the brain and is responsible for many essential functions. Damage to even small brain stem areas often causes death because reflexes essential for survival are integrated in the brain stem, whereas relatively large areas of the cerebrum or cerebellum may be damaged without being life-threatening. All but two of the 12 cranial nerves enter or exit the brain through the brain stem.