I understand that they are concentrated under cell membrane and can contract, but the details aren't very clear. How do they attach to membrane, and in what direction do they pull? Do they draw two points of cell membrane together or what? Also, actin in muscles doesn't just contract itself but anchors to myosin and "crawls" along it: it's not actin that contracts, but the entire actin-myosin complex. Does something similar happen in microfillaments?