Myofibrils (obsolete term: sarcostyles) are cylindrical organelles. They're found within muscle cells. They're bundles of actomyosin filaments that run from one end of the cell to the other and are attached to the cell surface membrane at each end. Actomyosin motors are important in muscle contraction (relying in this case on "classical myosins") as well as other processes like retraction of membrane blebs, filiopod retraction, and uropodium advancement (relying in this case on "nonclassical m… (More on Myofibril)