The nervous system is responsible for coordinating all body activity and is divided into the central nervous system and peripheral nervous system. The central nervous system consists of the brain and spinal cord and controls everything in the body. It is made up of over 10 billion nerves and is divided into the cerebrum, cerebellum, and brain stem, each controlling different functions like thinking, balance, and heartbeat. The peripheral nervous system is made of nerves and sense organs and carries messages between the central nervous system and the rest of the body.