Central nervous system
The central nervous system is the part of the nervous system consisting of the brain and spinal cord. The central nervous system consists of the two major structures: the brain and spinal cord. The brain is encased in the skull, and protected by the cranium. The spinal cord is continuous with the brain and lies caudally to the brain, and is protected by the vertebrae The spinal cord reaches from the base of the skull, continues through or starting below the foramen magnum, and terminates roughly level with the first or second lumbar vertebra, occupying the upper sections of the vertebral canal.
The CNS is contained within the dorsal body cavity, with the brain housed in the cranial cavity and the spinal cord in the spinal canal. In vertebrates, the brain is protected by the skull, while the spinal cord is protected by the vertebrae. The brain and spinal cord are both enclosed in the meninges. In central nervous systems, the interneuronal space is filled with a large amount of supporting non-nervous cells called neuroglial cells.