Now, if the bear is that size I'm clearly not going to run away. But if the bear is a large bear and if I panic I'm going to run. Now, when I run, what happens inside my body? Well, somehow my cells know to generate more ATP molecules because the skeletal muscle and the cardiac muscle will need those ATP molecules to basically increase the rate of contraction. So for instance, the heart will be able to pump more blood and the rate at which the heart actually pumps the blood to the tissues will increase as a result of those ATP molecules. Now, the question is how do the cells know to basically begin carrying out these processes?