The spinal cord is the main pathway of communication between the brain and the rest of the body. It is a long, fragile, tubelike structure that extends downward from the base of the brain. The cord is protected by the back bones (vertebrae) of the spinal column which are separated and cushioned by disks made of cartilage.
Along the length of the spinal cord, 31 pairs of spinal nerves emerge through spaces between the vertebrae. The spinal nerves connect with nerves throughout the body. Each spinal nerve has two nerve roots (except the first, which has no sensory root). The root in the front, the motor root, transmits inpulses from the spinal cord to the muscles. The root in the back, the sensory root, carries sensory information (about touch, position, pain, and temperature) from the body to the spinal cord.
The spinal column is divided into four areas: cervical (neck), thoracic (chest), lumbar (lower back), and sacral (pelvis). Each area is referred to by a letter (C, T, L, or S). The vertebrae in each area of the spine are numbered beginning at the top. For example, the first vertebra in the cervical spine is labeled C1, the second in the cervical spine is C2, the second in the thoracic spine is T2, the fourth in the lumbar spine is L4, and so forth.