MUSCLE PHYSIOLOGY

Detailed explanation-1: -A sarcomere is defined as the segment between two neighbouring Z-lines (or Z-discs). In electron micrographs of cross-striated muscle, the Z-line (from the German “zwischen” meaning between) appears in between the I-bands as a dark line that anchors the actin myofilaments.

Detailed explanation-2: -The Z line (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.

Detailed explanation-3: -Z-lines define the boundaries of each sarcomere. The M-line runs down the center of the sarcomere, through the middle of the myosin filaments. The I-band is the region containing only thin filaments. The H-zone contains only thick filaments.

Detailed explanation-4: -As we take a closer look at the structure of a sarcomere, you’ll notice these zigzag sections that mark the end point of each sarcomere. These are called Z discs or Z lines, and they allow for the attachment of the thin (actin) filaments, as well as an elastic protein called titin.