The autonomic nervous system gets its name from the fact that it relates to autonomous*or self-regulatory activities such as digestion and circulation, which continue even when we are asleep or unconscious. Impulses from the brain and spinal cord travelling along the autonomic nerves, cause blood vessels to dilatwr contract, digestion to slow or speed up, body temperature to rise or fall, all according to the changing requirements.
The autonomic system consists of two sets of nerves: The sympathetic nerves which stimulate the body to react in a situation of stress or danger by increasing the blood pressure, heart beat rate, breathing and flow of blood to the muscles, and by decreasing the flow of blood to the digestive organs and kidneys. All these reactions are a preparation for a sudden expenditure of energy in either fighting or fleeing. The parasympathetic nerves which prepare the body for relaxed functions.
The autonomic nervous system does, however, interact with conscious nervous activity. For example, it is well known that anxiety and mental tension can affect digestion, they tven cause peptic ulcers or high blood pressure. A child's dislike for school may make him sick every morning, without his being conscious of the connection. Under certain conditions, with lot of practice, some people have found it possible to consciously control heart beat, or blood pressure, or body temperature or breathing rate and oxygen intake; others may regulate the feeling of pain or even correct malfunction of an organ. But these are extraordinary and excepticnal abilities ckveloped with tremendous expenditure of time and effort.