Explain the structural differences between the thick and thin myofilaments.

A THICK FILAMENT IS COMPOSED OF SEVERAL HUNDRED MOLECULES OF THE PROTEIN MYOSIN. EACH MYOSIN MOLECULE IS SHAPED LIKE A GOLF CLUB, WITH THE STRAIGHT PORTION OF THE MOLECULE ENDING IN A GLOBULAR HEAD, OR CROSS-BRIDGE. THE CROSS-BRIDGES OCCUR ON EACH SIDE OF A SARCOMERE BUT NOT IN THE MIDDLE. A THIN FILAMENT CONSISTS OF TWO INTERTWINING STRANDS OF THE PROTEIN ACTIN, WITH TWO OTHER PROTEINS, CALLED TROPOMYOSIN AND TROPONIN, ASSOCIATED WITH THE ACTIN.