Chemoreceptors in the periphery sense changes in pH or PCO2 of the Blank 1, which will trigger the B… Show more Chemoreceptors in the periphery sense changes in pH or PCO2 of the Blank 1, which will trigger the Blank 2 area in the medulla to increase contraction of thoracic muscles, leading to Blank 3, helping to expel excess carbon dioxide. • Show less