Re: respiratory system

Reference: Pathophysiology: Concepts of Altered Health States by Carol Porth, 1990, 3rd edition

The human respiratory system is considered involuntary because the respiratory center, located in the brain stem, "drives" or regulates respiration without any conscious effort on behalf of the individual. Respiratory innervation is considered part of the autonomic or involuntary nervous system, with an interesting "overlay" by the voluntary nervous system that allows conscious control. Thus an individual can consciously override the system -- use the voluntary nervous system -- by stopping, slowing down, or speeding up the rate of respiration, or by changing the depth of respiration! Without this control, human speech would be impossible.

The autonomic control of respiration is monitored by: 1) chemoreceptors (central and peripheral) and 2) lung receptors. Chemoreceptors include loci in the brain that can detect levels of carbon dioxide (CO2) in the blood. Too much and you increase your rate of respiration, too little and you decrease the rate. In young children, breath holding - as all new parents quickly realize, is very limited as eventually the increasing carbon dioxide content of the blood (resulting from lack of air exchange) will be detected by the chemoreceptors and respiration will be restarted spontaneously. This arrangement can be viewed from an evolutionary standpoint as a means of survival during sleep or compensating for periods of unconsciousness (fainting or trauma).

The term "drive" has so many implications that is seems to me of little use in this physiological setting; it is not a psychological drive, such as hunger, love, and fatigue, but can be used (see above) to state that the brain stem drives respiration.