Myofilaments of Myofibrils
Myofibrils consist of two kinds of myofilaments. The thick filaments and the thin filaments. The thick filaments are made up of myosin and the thin filaments are of actin and the regulatory proteins troponin and tropomysin. The thick filaments are confined to A-band whereas the thin filaments extend from the Z-line and enter into A-band between thick filaments.
The I-band contains only thin filaments. In the region of overlap between thick and thin filaments, the adjacent thick and thin filaments interact with each other by forming cross bridges. The cross bridges are projections of myosin molecules whose interaction with actin molecules generate the force for the muscle contraction.