Nervous system, human: The sum total of the tissues that record and distribute information within a person, and does so by electrical and chemical means.
The nervous system has two distinct parts -- central and peripheral. The central part is made up of the brain and spinal cord. Together they are the central nervous system (CNS). The peripheral part of the nervous system is said to be peripheral because it is outside the CNS. The function of the peripheral nervous system is to transmit information back and forth between the CNS and the rest of the body.
The human nervous system contains approximately 10 billion nerve cells. These neurons are the basic building blocks of the nervous system. Neurons consist of the nerve cell body and various extensions from the cell body. These extensions, or processes, are the dendrites (branches off the cell that receive electrical impulses), the axon (the electrical wiring and conduit tube that conducts impulses), and specialized endings (terminal areas to transfer impulses to receivers on other nerves or muscles).