What is the cross arm in the heavy meromyosin (HMM) component?

.Each "F" actin is a polymer of monomeric "G" (Globular) actinsTwo filaments of another protein, tropomyosin also run close to the "F" actins throughout its length.In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.The thick filament in a myofibril is made up of many monomeric proteins called Meromyosins.The HMM component consists of the head and short arm of a meromyosin.The thick filament in a myofibril is made up of many monomeric proteins called Meromyosins.The HMM component consists of the head and short arm of a meromyosin. The globular head in the HMM component is an active ATPase enzyme and has binding sites for ATP and active sites for actin.The cross arm in the HMM component refers to the head and short arm projecting outwards at regular distance and angle from each other from the surface of a polymerised myosin filament.