Actin (left, in green) and myosin (right, in red) in a cell that is moving from left to right. Notice the thick band of actin at the front of the cell, which is pushing the cell front forwards. The actin is also bunched up in a line across the middle of the cell, where the myosin is pulling it together.

Figure courtesy of Gary Borisy.
Reproduced from the Journal of Cell Biology 1997, vol. 139, pp397-415 by copyright permission of The Rockefeller University Press.