Medicine & USMLE

Microfilaments (Actin Filaments)

  1. Microfilaments (Actin Filaments)
  2. Intermediate Filaments
  3. Microtubules


Microfilaments are long, thin filaments in the cytoskeleton made of actin, which is why they are also called actin filaments. These actin filaments are dynamic, and rapid addition and removal of actin molecules to the ends of a microfilament can both rearrange the cytoskeleton and enable treadmilling. The dynamic rearrangement of the actin filaments is necessary for gross cellular movements, such as that seen in cytokinesis.  Other key roles include muscle contraction as a component of the sarcomere, as well as being the cytoskeletal component of Tight Junctions.

Key Points

  • Microfilaments
    • Also called actin filaments
      • Composed of actin
    • Involved in gross movement of the cell
      • Helps with cell division in cytokinesis and amoeboid movement of macrophages
      • Movement mediated by dynamic rearrangement of cytoskeleton, in contrast vs. microtubule-mediated cilia and flagella
    • Component of muscle sarcomeres
    • Cytoskeletal component in Tight Junctions
    • Thin diameter (~6 nm)
    • Dynamic - changes length by adding/removing actin monomers to ends
      • Can lead to treadmilling
        • polymerization at one end and depolymerization at the other