Talk about the bands forming the sarcomere.

The dark band A is formed of thick myosin filaments and thin actin filaments arranged in a parallel manner, while the I band is formed of only thin actin filament. Band A comprises in its middle a clearer transverse zone called M zone (dark transverse line). Myosin molecule comprises a cylindrical rod or axis (tail) which terminates at one of its ends by 2 spherical heads that interact with actin through actin binding sites, and have ATPase activity necessary for hydrolysis of ATP.