The 3-D sarcomere lattice is composed of thick and thin filaments arranged in an overlapping hexagonal lattice with a geometry that is consistent with the mean spacing measured in vertebrate striated muscle. (A) Myosin filaments extend from the central M-band toward Z-lines and actin filaments extending from Z-lines forming a hexagonal arrangement in cross section. (B) The actin monomers are helically arranged in a double strand helical structure and orientationally favorable myosin-binding sites on actin filament or target zones associated with myosin heads are shown in red. Each myosin molecule is attached to the trunk of myosin filament via the S2 rod and has two heads (S1 fragments) at the free end, but only one head per dimer is shown. The pairs of myosin heads form a triple helix along the myosin filament. The myosin heads are arranged in layers and at each layer form a “crown” with three pairs of heads. The crowns $ℒc$ = 1, 2, and 3 are axially separated by 14.3 nm and rotated by 40°, forming different angular arrangements with actin filaments, but only those that might interact with the actin filament are shown. In the axial direction, each pair of heads and multiple binding sites (target zones) on surrounding actin filaments form a large number of arrangements defined by the relative axial distances, x, between the unstrained position of the myosin head or cross-bridge and the nearest actin-binding site, and azimuthal angles α and β as defined in Fig. 4. (C) The hexagonal sarcomere lattice with 2:1 actin to myosin filament ratio shows in the azimuthal plane that up to three myosins can attach to each actin filament. The spatial arrangement of crowns $ℒc$ = 1 interacting with six surrounding actin filaments is shown. (D) The heads in crowns $ℒc$ = 2 and 3 have different azimuthal spatial arrangement relative to binding sites on the actin filaments displayed by azimuthal angles α and β.