During contraction, the filaments slide past he thick filaments, shortening the sarcomere. The thick and thin filaments do the actual work of a muscle, and the way they do this is pretty cool. Thick filaments are made of a protein called myosin. At the molecular level, a thick filament is a shaft of myosin molecules arranged in a cylinder. Thin filaments are made of another protein called actin. The thin filaments look like two strands of pearls twisted around each other.
