The Nervous Systems

Together, the spinal cord and the brain make up the central nervous system (CNS).

The CNS controls most functions of the body, but it is not the only nervous system in the body. The peripheral nervous system (PNS) includes the nerves that project to the limbs, heart, skin, and other organs outside the brain. The PNS controls the somatic nervous system, which regulates muscle movements and the response to sensations of touch and pain, and the autonomic nervous system, which provides nerve input to the internal organs and generates automatic reflex responses. The autonomic nervous system is divided into the sympathetic nervous system, which mobilizes organs and their functions during times of stress and arousal, and the parasympathetic nervous system, which conserves energy and resources during times of rest and relaxation.

The spinal cord acts as the primary information pathway between the brain and all the other nervous systems of the body. It receives sensory information from the skin, joints, and muscles of the trunk, arms, and legs, which it then relays upward to the brain. It carries messages downward from the brain to the PNS, and contains motor neurons, which direct voluntary movements and adjust reflex movements. Because of the central role it plays in coordinating muscle movements and interpreting sensory input, any kind of injury to the spinal cord can cause significant problems throughout the body.