Each spinal cord segment innervates a dermatome (see below and Figure 3.5). The spinal nerve contains motor and sensory nerve fibers to and from all parts of the body. The spinal cord is a cylindrical structure of nervous tissue composed of white and gray matter, is uniformly organized and is divided into four regions: cervical (C), thoracic (T), lumbar (L) and sacral (S), (Figure 3.1), each of which is comprised of several segments. These nerve roots join distally to form 31 pairs of spinal nerves. Two consecutive rows of nerve roots emerge on each of its sides. The spinal cord is 40 to 50 cm long and 1 cm to 1.5 cm in diameter. It is a vital link between the brain and the body, and from the body to the brain. The spinal cord extends from the foramen magnum where it is continuous with the medulla to the level of the first or second lumbar vertebrae. The spinal cord is the most important structure between the body and the brain.
Schematic dorsal and lateral view of the spinal cord and four cross sections from cervical, thoracic, lumbar and sacral levels, respectively.
