Protein kinase A is activated by a secondary messenger molecule that we'll talk about in a moment, cyclic amp. And once the protein kinase A is activated, it goes on to activate affected molecules. For instance, enzymes which carry out the breakdown of Glycogen into glucose. And then the glucose can be used by these, let's say, skeleton muscle cells to basically produce ATP molecules which themselves are used to basically contract the skeleton muscle. And once the skeleton muscle contracts, that is precisely what allows us to basically run away from that animal, from that bear. So carry out that particular type of physiological effect.