It is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. It is essentially the body's electrical wiring.
Structurally, the nervous system has two components: the central nervous system (the brain, spinal cord, and nerves) and the peripheral nervous system (sensory neurons, ganglia and nerves that connect to one another and to the central nervous system).
Functionally, the nervous system has two main subdivisions: the somatic, or voluntary, component (nerves that connect to one another and to the central nervous system and the autonomic nervous system (regulates certain body processes, such as blood pressure and the rate of breathing, that work without conscious effort).