Each myofibril consists of two sets of filaments: a thick set of filaments containing the protein myosin and thin set of filaments containing the protein actin. These two sets are arranged within the myofibril.
In the center of the light I-band the line is called Z-line. Actin filaments are attached to these Z lines (or Z disc) and extend in both directions.
The thin filament (I bands) extend longitudinally from Z lines, which the thick filament (A band) span the gaps between the tips of the opposing actin units.
Components of myofibrils