The nervous system consists of highly specialized cells designed to transmit information rapidly between various parts of the body. Topographically it can be divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The brain and spinal cord constitute the CNS, which lies within the skull and vertebral canal, while nerves in the PNS connect the CNS with all other parts of the body.

The CNS is a massive collection of nerve cells connected in an intricate and complex fashion to subserve the higher order functions of the nervous system, such as: thought, language, emotion, control of movement and the analysis of sensation. It is isolated from the rest of the body; its cardinal characteristic is that it is located wholly within the skull and vertebral canal.

The PNS consists of cells that connect the CNS with the other tissues of the body. These cells are aggregated into a large number of cable-like structures called nerves, which are threaded like wires throughout the tissues of the body.