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Why can breathing increase in response to carbon dioxide even after the carotid and aortic bodies are removed?

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A pine grosbeak with pink and gray plumage perches on a branch, eating red berries among autumn foliage. — Chemoreception Animals, such as this pine grosbeak, use chemoreception to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviors such as food preference and defense.

Breathing continues to increase in response to elevated carbon dioxide levels even after the removal of the carotid and aortic bodies because of the presence of central chemoreceptors. These receptors are located near the ventral surface of the medulla in the brain.1

While specific chemoreceptor cells have not been conclusively identified in this region through microscopic examination, it is widely accepted that these additional receptors detect changes in the partial pressure of carbon dioxide or the resulting acidity in the surrounding fluid. Some researchers hypothesize that these respiratory responses may be direct, potentially involving the modulation of excitatory and inhibitory inputs from nearby vasomotor neurons, which are responsible for regulating blood pressure. Others suggest that the chemoreceptors sensitive to carbon dioxide may be more diffusely distributed throughout the brain.1