Muscle Physiology 1. Skeletal muscle is striated caused by the arrangement of proteins in the thin and think myofilaments. The number of muscle cells in a whole muscle depends on the size of the whole muscle. The dark A bands contain thick myofilaments. The light I bands contain thin myofilaments. 2. Thin myofilaments are made up of 3 proteins: a) GActin Globular protein linked together to form a twostranded chain. Each Gactin molecule contains a myosin binding site.