The Autonomic System

Blue= parasympathetic
Red= sympathetic

The autonomic system is also in the perepherial nervous system. " The ANS has far reaching effects, including: heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition - (the discharge of urine), and erection. Whereas most of its actions are involuntary, some ANS functions work in tandem with the conscious mind, such as breathing. The ANS is divided into two limbs, the parasympathetic nervous system which is primarily involved in relaxation, and the sympathetic nervous system which causes the body to become more active as in the "fight or flight" response.

The ANS is a classical term, widely used throughout the scientific and medical community. Its most useful definition could be: the sensory and motor neurons that innervate the viscera. These neurons form reflex arcs that pass through the lower brainstem or medulla oblongata. This explains that when the central nervous system (CNS) is damaged experimentally or by accident above that level, a vegetative life is still possible, whereby cardiovascular, digestive and respiratory functions are adequately regulated."

It is divided into the sympathetic and parympatheic divisions. While their functions are different they do share some similar features. They function automatically and it's usually involuntary. They innervate all internal organs. They utilize two nuerons and one ganglian for each impulse.

The sympathetic division is most usefull during emergency situations. It accelerates the heartrate and dialates the bronchial tube. It inhibits digestion during an emergency situation because that is not considered a priority at the time.

The parasympathetic division includes a few cranial nerves as well as fibers that come from the bottom part of the spinal cord. This division is also known as the "housekeeping division" because it promotes all internal responsed when we are relaxed; ie, contracted pupils, slow heartbeat, etc.