The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. The spinal cord is divided into cervical, thoracic, lumbar, and sacral regions, though because the spinal cord is shorter than the vertebral column, these regions do not line up with their corresponding vertebral levels. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Like the brain, the spinal cord is surrounded by 3 layers of connective tissue, collectively known as the meninges; these layers are the dura mater, arachnoid mater, and pia mater. The spinal cord is supplied by 1 anterior and 2 posterior spinal arteries.