The central nervous system is comprised of the brain and the spinal cord. The brain receives sensory information from the nerves that pass through the spinal cord and from other nerves as well, such as those from sensory organs involved in sight and smell. Once received, the brain processes the sensory signals and initiates responses.

The spinal cord is a principle conduit of sensory information to and from the brain. Information flows to the central nervous system from the peripheral nervous system, which senses signals from the environment outside the body (sensory-somatic nervous system) and from the internal environment (autonomic nervous system). The brain's responses to incoming information flow through the spinal cord nerve network to the various effector organs and tissue regions where the target responsive action will take place.

Both the spinal cord and the brain are made up of...