noun, plural: thin filaments
Myofilaments make up the myofibril. The myofibrils are contractile threads that extend along the length inside the striated muscle fiber. There are two main types of myofilaments. These are the thin filaments and the thick filaments. The thin filaments are approximately 7-9 nm in diameter. They are attached to the z discs of the striated muscle. Each thin filament is made up of three proteins: (1) actin, (2) troponin, and (3) tropomyosin. Actin though is the main protein component of the thin filament. There are about 300-400 globular actin molecules attached from end to end to form the helical strands of the thin filament, now called F actin (being fibrous). Each actin molecule has a binding site for a myosin cross bridge or head during the process of contraction.1 Another protein in the thin filament is troponin. Troponin is a complex of three protein subunits, and occurs at about every 40 nm along the filament. Tropomyosin is a rod-shaped protein that is about 40 nm in length. Two strands of tropomyosin molecules run along the helical actin filaments and is associated with troponin. Troponin molecule has a binding site for Ca++. In the presence of Ca++, the troponin binds to it and moves the tropomyosin to allow contraction.
1 Thin Filaments in Skeletal Muscle Fibers. In Get Body Smart. Retrieved from []
2 muscle. (2015). In Encyclopædia Britannica. Retrieved from []