Convergence of Stimuli in Arterial Chemoreceptors

Abstract

A single chemoreeeptor fibre of the carotid sinus nerve responds both to hypoxia and to hypercapnia/acidity of the arterial blood. These reactions have been well brought out by such recent studies as those of Lahiri¹ which he has illustrated in a figure in his paper at this symposium. If reactions to CO₂ are presented as a series of CO₂ response curves at various intensities of hypoxia, the curves appear as a fan of approximately straight lines which have a steeper slope the more intense the hypoxia. It is when there is some degree of hypoxia that the effects of CO₂ become marked in the steady state, as Neil² has always emphasised, but if the P_CO2 arterial blood is changing, the effects of CO₂ on discharge are more striking, for adaptation of the response to a sudden change of P_CO2 marked, particularly in hyperoxia. Thus if a receptor is discharging at some steady initial level and the Pa_CO2 is suddenly raised, the discharge immediately rises along a steep transient response curve and then adapts down to lie upon the steady state curve.