And as our trophymycin, shown in blue, actually shifts, it exposes special binding sites on the actin filament known as our myosin binding site. So this is basically where our myosin heads found on the thick filament, actually bind to our thin filament. So this green region, which was blocked on this diagram is exposed as soon as our calcium binds onto our troponin. So this is our calcium, it binds onto our troponin, it changes its shape, which in turn changes the shape of our tropomycin and that exposes our myosin binding side. So this is step number two. Now, as soon as our binding side is exposed, right before the binding between the thick and the thin filament actually takes place, our myosin head has to basically hydrolyze an ATP molecule.