Autonomic System:

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.