When impulses are finally conveyed by nerve cells to muscle cells or glands, an action or movement is to be brought about in the body, the work of the muscular tissue comes last in the sequence. Movement of muscle cells is essential to bring about any activity. When cells contract to change their shape, movement occurs at cellular level. Muscle cells have the ability to change their shape due to a special type of protein. Besides, due to these same proteins, cells become able to respond to electrical impulses of nerves.