2 Ultrastructure of myofiber ∵··· ① myofibril: composed of thick myofilament: 1.5 um long, 15nm in diameter ● composed of myosin: rob: in bundles 肌动蛋白单体原肌球蛋白 肌原蛋白 In T -head 细肌丝 cross bridge binding (3 site(ATPase activity) 肌球蛋白杆 (横桥)2) Ultrastructure of myofiber ① myofibril: composed of ---thick myofilament: 1.5 um long, 15nm in diameter composed of myosin: -rob: in bundles -head: cross bridge- binding site(ATPase activity)