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Your nervous system is composed of the central nervous system, the cranial nerves, and the peripheral nerves. The brain and spinal cord together form the central nervous system. The cranial nerves connect the brain to the head. The four groups of nerves that branch from the cervical, thoracic, lumbar, and sacral regions of the spinal cord are called the peripheral nerves.

Parts of the nervous system

Illustration provided by: Leslie Laurien, MSMI

Glossary

Brain
The brain's primary role is to function as the body's control center. This organ receives and interprets nerve signals from every part of the body and initiates the appropriate response. These responses include adjustments in internal bodily functions (eg, heart rate and temperature), movement, speech, and emotions and consciousness.

Spinal cord
The spinal cord is a cylinder of nerve tissue that runs down the center canal in the spine. The nerve fibers in the spinal cord transmit sensory information toward the brain and motor signals to the appropriate parts of the body. The spinal cord also handles some automatic motor responses to sensory information by itself.

Cervical spinal nerves (C1 to C8)
These nerves (eight pairs) supply the back of the head, the neck and shoulders, the arms and hands, and the diaphragm.

Thoracic spinal nerves (T1 to T12)
These nerves (12 pairs) supply the chest, some muscles of the back, and parts of the abdomen.

Lumbar spinal nerves (L1 to L5)
These nerves (five pairs) supply the lower parts of the abdomen and the back, the buttocks, some parts of the external genital organs, and parts of the legs.

Sacral spinal nerves (S1 to S5)
These nerves (five pairs) supply the thighs and lower parts of the legs, the feet, most of the external genital organs, and the area around the anus.