The autonomic or involuntary nervous system controls many functions of the body that take place automatically such as digestion, respiration and circulation.

The autonomic nervous system has two divisions. These are:

• the sympathetic system, and
• the parasympathetic system.

Nerves of the autonomic system belong to the peripheral nervous system. The sympathetic nerves originate from the spinal cord at the thoracic and first two lumbar segments. The parasympathetic nerves originate from the brain stem and the sacral segments of the spinal cord.