A network of fibres permeating the matrix of living eukaryotic cells that provides a supporting framework for organelles, anchors the plasma membrane and certain cell junctions, facilitates cellular movement, conveys vesicles and other components around the cell, and provides a suitable surface for chemical reactions to take place. Reorganization of the cytoskeleton is also responsible for changes in cell shape and cell migration that occur when organs are formed during embryonic development. The cytoskeletal fibres are composed of microtubules, intermediate filaments, and microfilaments.

http://www.bms.ed.ac.uk/research/others/smaciver/Cyto-Topics/actinpage.htm In-depth collection of resources about actin, the cytoskeleton, and related structures, hosted by Edinburgh University