CNS Gray matter: cell bodies and short nonmyelinated fibers. White matter: contains myelinated axons that run together in bundles called tracts. Meninges: membranes covering the brain and spinal cord. (dura mater (outermost), arachinod, pia mater (innermost)). The subarachinod area is full of cerebrospinal fluid.

CNS: Spinal Cord Extends from the base of the brain through the foramen magnum of the cranium. It is protected by the vertebral column and is located in the vertebral foramen. The spinal cord ends at L1.

CNS: Spinal Cord Anatomy Central canal with gray matter surrounded by white matter. The central canal contains cerebrospinal fluid. Portions of sensory and motor neurons reside in the gray matter as do interneurons. The posterior root of a spinal nerve enters here and the anterior root (containing motor fibers) exits the gray matter. Spinal nerves are created by the joining of these two roots (part of PNS). White matter is made of ascending and descending tracts that take data to and from the brain. Because these tracts cross just after they enter or exit the brain, the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body.