A 10-min. tutorial video gifted by the creative folks at Crash Course showcasing the cells of your muscles. Join 2.6 million viewers in an exploration of muscles with a look at the complex and important relationship between actin and myosin myofilaments… and more like: smooth, cardiac, and skeletal muscles create movement; sliding filament model; skeletal muscles made of protein fiber bundles; and, calcium and ATP cause binding and unbinding.