Respiratory chemosensitivity in the medulla oblongata.

Respiratory regulation is considered as a feedback mechanism serving the homeostasis of the hydrogen ion concentration in brain extracellular fluid during rest as well as during exercise. Only in hypoxia the working range of the regulator is shifted in such a way that a sufficient O2 partial pressure is maintained at the cost of hydrogen ion concentration. The main sensing element of the regulator is the ‘central' chemosensitivity. The location of the chemosensitive mechanism in two plaques of a superficial layer of the ventral medulla oblongata is amply discussed. This region is separated from the respiratory centres and provides the centres with a tonic pH sensitive impulse flow. It is not necessary to assume additional chemosensitivity of the centres. In muscular exercise additional impulses reach the centres which are able to compensate the otherwise expected deviation of extracellular pH in brain caused by the increased CO2 production in the body. If the brain is considered as a computer the described homeostatic mechanism may be viewed as assuring the reproducibility of the nerve cells as units of the computer.