Which part of the brain contains central chemoreceptors that monitor CO2 levels in blood?

Explanation

The respiratory centre of the medulla carries chemoreceptors that detect the fall in pH caused by rising carbon dioxide and increase the rate and depth of breathing until the excess is blown off. Oxygen level is monitored elsewhere, by peripheral receptors in the aorta and carotid arteries, and acts only as a weak backup stimulus. This is why holding the breath becomes unbearable from carbon dioxide build up rather than from lack of oxygen.