Z-disks are the lateral boundaries of a single sarcomere. In electron micrographs of cross striated muscle the Z-line appears as a series of dark lines. They represent a key interface between the contractile apparatus and the cytoskeleton. The Z-disk (from the German "Zwischen") largely consists of alpha-actinin homodimers organized in an antiparallel fashion, thereby providing a backbone for the insertions of actin-based thin filaments, as well as titin and nebulin/nebulette. Z-disks of neighbouring sarcomeres are aligned in parallel and connected via the intermediate filament protein desmin.
