The structural basis of muscular contraction.

During the past 25 years, there have been important developments in the techniques of low-angle X-ray diffraction and electron-microscopy, as applied to biological material. In the case of muscle, these developments have made it possible to study n-iany of the molecular changes which occur during contraction. According to the present structural model, contraction is brought about by a relative sliding motion of arrays of two different types of molecular filaments. The sliding force is generated by the cyclical action of cross-bridges between these myosin and actin filaments. The experimental evidence which led to this picture is described, together with the technical developments involved.