Autonomic Nervous System
The organs of our body are controlled by many systems in order to function correctly and efficiently in order to survive within the environment we live in. These include the heart, stomach and intestines and other vital organs and body systems. All of the systems in our body are regulated by a part of the nervous system called the autonomic nervous system (ANS). The ANS is part of the peripheral nervous system and it controls many organs and muscles within the body. Rather bizarrely we are unable to determine or feel its presence in our bodies as it is working involuntary, as a reflexive manner. A common example of this involuntary action is best understood when you think about your circulatory system. We do not notice when blood vessels change size or when our heart beats faster, unless of course the change is shockingly dramatic. But otherwise it's an internal change to your bodies internal environment that you do not have any mental or physical control upon.
However, it is known that, some people can train themselves to control some functions of the ANS such as heart rate or blood pressure. Deep sea diving with out the use of underwater breathing equipment, is an efficient use for this technique as it allows you to reduce your heart rate. This then allows the bodies oxygen consumption rate to be reduced, resulting in an overall increase in the ability to hold your breath to dive deeper depths (up to 60ft has been recorded). But don't be mislead, this is not an ability that anyone could simply undertake on the family holiday. It requires strict self-control and powerful meditational skills.
The Sympathetic and parasympathetic Nervous System:
The ANS is divided into two parts, the Sympathetic Nervous System and the Parasympathetic Nervous System. These have opposite (antagonistic) effects on the organs, which they supply. Generally, the sympathetic system prepares the body
References: Books, - Biological Science 2: third edition – D.J. Taylor, N.P.O. Green, G.W. Stout - Life The Science of Biology: Seventh edition – Purves, Sadava, Orians, Heller Web, - Journal of Neurophysiology: http://jn.physiology.org - W, Gelber S, Orr-Urtreger A, Armstrong D, Lewis RA, Ou CN, Patrick J, Role L, De Biasi M, and Beaudet AL. Megacystis, mydriasis, and ion channel defect in mice lacking the alpha3 neuronal nicotinic acetylcholine receptor. Proc Natl Acad Sci USA 96: 5746–5751, 1999 - www.breathing.com/articles/autonomic-nervous-system.htm - www.integrativehealthcentre.com/autonomicresponse1.htm