Fig. 1

Sarcomere and M-band. A The muscle sarcomere as shown in an electron micrograph of longitudinally cut mouse heart muscle. B Schematic representation of the sarcomere shown in A. Myosin thick filaments are shown in blue, thin actin filaments in orange, sarcomeres borders (Z-discs) in black and the central zone (M band) in grey/white. The darker colors of Z-discs and A-band reflect on the striated appearance of sarcomere on electron micrographs. C A schematic representation of M band structure comprising of a set of M-lines (which appear as lighter lines on electron micrographs). D Transverse M-band lattice schematic representation based on electron microscopy sections. Blue circles indicate the positions of myosin filaments, small pink circles show the positions of linking filaments. The black lines indicate the positions of the linking material