The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord, it integrates the received information, coordinates and influences the activity of all parts of the bodies of bilaterally symmetric animals—that is, all multicellular animals except sponges and radially symmetric animals such as
Many people consider the retina and the optic nerve (cranial nerve II), as well as the olfactory nerves (cranial nerve I) and olfactory epithelium as parts of the CNS, synapsing directly on brain tissue without intermediate ganglia.
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.