The carotid bodies are the primary peripheral chemoreceptors. They respond to a fall in blood pO2, a rise in blood pCO2 and consequent fall in pH by releasing neurotransmitters. These increase the firing frequency of the carotid sinus nerves which then correct the pattern of breathing via an action at the brainstem. It is now generally accepted that the type 1 or glomus cells are the chemosensory element within the carotid body. However, the precise mechanism by which a fall in pO2 excites the neurotransmitter rich type 1 cells has been the subject of hearty debate for decades now.