So this is our sarcomere. The sarcomir consists of these thin filaments that are composed of globular proteins known as actin. And we also have the thick filaments, shown in purple, that are composed of our protein known as myosin. So let's discuss how they actually interact. So let's label this step as step number one. So, basically, the release of our calcium into the cytoplasm, into the cytosol of the cell, that is step number one.