Question

multiple choice question
the central chemoreceptors respond to____, not to____.
o carbon dioxide; hydrogen ions
o hydrogen ions; carbon dioxide

Explanation:

Central chemoreceptors are located in the brainstem. They are sensitive to changes in the pH of cerebrospinal fluid. Carbon dioxide (\(CO_2\)) can cross the blood - brain barrier. When \(CO_2\) enters the cerebrospinal fluid, it reacts with water (\(H_2O\)) to form carbonic acid (\(H_2CO_3\)), which then dissociates into hydrogen ions (\(H^+\)) and bicarbonate ions (\(HCO_3^-\)). The change in \(H^+\) (pH change) is what the central chemoreceptors actually respond to. But they do not directly respond to \(CO_2\) in the sense that if \(CO_2\) cannot enter the cerebrospinal fluid (e.g., if there is no conversion to \(H^+\) due to lack of water in the reaction environment in a non - biological sense), they won't be activated. So, they respond to hydrogen ions (indirectly due to \(CO_2\) entry and reaction) and not directly to carbon dioxide in the initial, non - reacted form.

Answer:

hydrogen ions; carbon dioxide