Now, skeleton muscle cells are responsible for creating and generating voluntary motion. And so when skeleton muscle cells break down glycogen into glucose, they use that glucose to basically produce, reduce the ATP molecules, the energy molecules needed to create voluntary motion. On the other hand, liver cells are responsible for actually maintaining and regulating the proper blood glucose levels in our body. And so when liver cells actually break down glycogen into glucose, they can release that glucose into the blood and that helps our body maintain the correct level of glucose in our cardiovascular system. Now, what I'd like to discuss in this lecture is what ultimately is the signal that initiates the breakdown of glycogen in our liver cells as well as in our skeletal muscle cells. So let's begin by focusing on liver cells.