List the 3 molecules used by the cell to sense metabolic need and the proteins which sense them.Explain the effects that the absolute and relative refractory periods have on the initiation and propagation of action potentials. Identify the channels that underlie each of these phenomena and how they contribute to the effects that you described. In the diagram of the action potential provided, choose the letters that correctly identify the two different periods. -D ? B E h A F A 2015 sonoWhat is gastrin and what is its role in digestion? What is the role of gastric acid in digestion?