As the name indicates, the cytoskeleton is responsible for maintaining of the normal shape of the cell. It also facilitates the transport of substances across the cell and the movement of cellular organelles. For example, the interaction between actin-containing filaments and the protein myosin creates pseudopods. In the cells of the phagocytic defense system, such as macrophages, the cytoskeleton is responsible for the plasma membrane projections that engulf the external material to be interiorized and attacked by the cell.