The Sliding Filament Theory
The sliding of myosin and actin filaments causes muscles to contract. There are many forms of muscle contraction including contraction of the skeletal muscle, the heart and gut peristalsis all of which require the well regulated movement of the ATP-dependent sliding filaments. Each sarcomere is made up of a highly organised sequence of thick and thin filaments. The thin filaments are mainly made up of actin along with associated proteins. These filaments are all attached by their ends to a structure called a Z disc, the other end reaches parallel into the structure overlapping the thick filaments which are made up of myosin, each filament is evenly spaced between the other. Sarcomere shortening is not caused by the contraction or shortening of the actual filaments but by the sliding of the myosin filaments past the actin filaments.