(myofilament) Any of the smallest contractile units of a myofibril (striated muscle fiber).

Submicroscopic filaments composed chiefly of actin, found in the cytoplasmic matrix of most cells, often in close association with the microtubules; may play a role in cell and organelle movement and in supportive and cytoskeletal function.

(actin filament) A filamentous structure formed of a two-stranded helical polymer of the protein actin and associated proteins. Actin filaments are a major component of the contractile apparatus of skeletal muscle and the microfilaments of the cytoskeleton of eukaryotic cells. The filaments, comprising polymerized globular actin molecules, appear as flexible structures with a diameter of 5-9 nm. They are organized into a variety of linear bundles, two-dimensional networks, and three dimensional gels. In the cytoskeleton they are most highly concentrated in the cortex of the cell just beneath the plasma membrane.

(actin filament) The finest filamentous element of the cytoskeleton, having a diameter of about 5 nm and consisting primarily of actin.

(actin cytoskeleton) Fibers composed of MICROFILAMENT PROTEINS, which are predominately ACTIN. They are the smallest of the cytoskeletal filaments.

(actin cytoskeleton) The part of the cytoskeleton (the internal framework of a cell) composed of actin and associated proteins. Includes actin cytoskeleton-associated complexes.