Brain

The brain stem is the stalk of the brain, and is continuous with the spinal cord. It consists of the medulla oblongata, pons, and midbrain. A part of the brain stem, the medulla oblongata is a continuation of the spinal cord. All the messages that are transmitted between the brain and spinal cord pass through the medulla via fibers in the white matter. The fibers on the right side of the medulla cross to the left and those on the left cross to the right. The result is that each side of the brain controls the opposite side of the body. There are three vital centers in the medulla which control the heartbeat, the rate of breathing, and the diameter of the blood vessels. Centers that help coordinate swallowing, vomiting, hiccoughing, coughing, and sneezing are also located in the medulla. The reticular formation occurs partially in the medulla and in other parts of the central nervous system. The reticular formation operates in maintaining our conscious state. The pons (meaning bridge) conducts messages between the spinal cord and the rest of the brain, and between the different parts of the brain. The midbrain conveys impulses from the cerebral cortex to the pons and spinal cord. It also contains visual and audio reflex centers involving the movement of eyeballs and head.

Twelve pairs of cranial nerves originate in the underside of the brain, mostly from the brain stem. They leave the skull through openings and extend as peripheral nerves to their destinations. Cranial nerves include the olfactory nerve that brings messages about smell from the nose and the optic nerve that conducts visual information from the eyes.