Animals and plants possess an elaborate network of intracellular filaments that organize the transport of the cell’s building blocks with the precision of a well-engineered motorway. Some cargoes being transported within cells move over short distances (a millionth of a meter) whereas other cargoes, particularly those in nerve cells, must traverse distances as large as a meter from the cell body to the tip of a nerve terminal. All of this transport is produced by molecular motors, proteins that themselves are less than one ten millionth of a meter in size.
The first such molecular motor system was discovered in muscle. The filaments are composed of a protein called actin. During muscle contraction, actin filaments slide past one another, powered by a motor protein called myosin. This action of myosin was first described in muscle tissues in the 1950s and was discovered in the 1970s to power contractile events in non-muscle cells as well.