Transmission electron microscope image of a thin longitudinal section cut through an area of human skeletal muscle tissue. Image shows several myofibrils, each with distinct banding pattern of individual sarcomeres.

Image of muscle sarcomeres shows distinct banding pattern: the darker bands are called A bands(the A band includes a lighter central zone, called the H band), and the lighter bands are called I bands. Each I band is bisected by a dark transverse line called the Z-line). Paired mitochondria are on either side of the electron opaque Z-line. The Z-Line marks the longitudinal extent of a sarcomere unit.