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Human body

Nervous system

The nervous systemThe nervous systemThe nervous system consists of the brain, spinal cord and nerves. The spinal cord, a thick bundle of neurons that runs down your back, arises from the base of the brain. Spinal nerves that emerge from the spinal cord send branches to almost all parts of the body. The spinal cord relays nerve signals to and fro between body parts and the brain. In addition, cranial nerves arise directly from the brain and send branches to the head, face, neck and chest. Together, the brain and spinal cord form the central nervous system. The nerves that fan out from the spinal cord and brain form the peripheral nervous system.

The structure of a neuronThe structure of a neuron

Nerve cells

Each nerve contains bundles of hundreds or thousands of nerve cells, called neurons. They carry electrical signals. Each neuron has a cell body with short projections, called dendrites, that receive signals, and a long, thin, wire-like axon, or nerve fibre, that transmits them. The spinal cord consists of large numbers of bunched neurons that form the "information superhighway" between the brain and the body.

The largest nerve in the body is the sciatic nerve, which extends from the bottom of the spinal cord down each leg. The nerve forms a flat, ribbon shape about 2 cm (0.75 inch) wide.

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