Motor nerves exit carrying messages to the muscles and organs informing them how to operate. In cross section, the central part of the spinal cord is vaguely h-shaped. This is where information travels up to the brain. Each segment of spinal cord communicates with a particuluar section of the body and with the segments directly above and below it. An important part of the spinal cord is what is known as the reflex arc .
Sensory nerves enter the spinal cord and synapse with small interneurons within.
These synapse with more interneurons and with exiting motor neurons. It is here that reflexes are stored, creating a short loop direct from sensation to action completely bypassing the brain. The medulla, pons, midbrain and certainm structures of the forebrain are also collectively known as the brain stem. Medulla Controls basic reflexes such as breathing and heart rate so damage to this area is invariably fatal. Because of the types of functions of the medulla, large doses of drugs that effect this area can also be extremely harmful.