So if we look on the microscope, our muscle will basically look like it's striped. And that's because of these z lines. So when a muscle actually contracts, the way that our sarcomir contracts is in the following way, as we'll see in the next lecture, these mycin heads basically attach to our actin, to our thin filament. And when they attach, they basically contract. And when they contract, they bring these actin, these thin filaments, close to one another and we have overlap taking place, but the entire length of our thick filament does not actually change. So this is when our sarcomir is basically relaxed.