<P> Also, all three of these proteins may have a role in inhibiting the ATPase activity of the myosin complex that otherwise provides energy to fuel muscle contraction . </P> <P> The myosin and actin are the contractile parts of continuous chains of tensile structures that stretch both across and between smooth muscle cells . </P> <P> The actin filaments of contractile units are attached to dense bodies . Dense bodies are rich in α - actinin, and also attach intermediate filaments (consisting largely of vimentin and desmin), and thereby appear to serve as anchors from which the thin filaments can exert force . Dense bodies also are associated with β - actin, which is the type found in the cytoskeleton, suggesting that dense bodies may coordinate tensions from both the contractile machinery and the cytoskeleton . Dense bodies appear darker under an electron microscope, and so they are sometimes described as electron dense . </P> <P> The intermediate filaments are connected to other intermediate filaments via dense bodies, which eventually are attached to adherens junctions (also called focal adhesions) in the cell membrane of the smooth muscle cell, called the sarcolemma . The adherens junctions consist of large number of proteins including α - actinin, vinculin and cytoskeletal actin . The adherens junctions are scattered around dense bands that are circumfering the smooth muscle cell in a rib - like pattern . The dense band (or dense plaques) areas alternate with regions of membrane containing numerous caveolae . When complexes of actin and myosin contract, force is transduced to the sarcolemma through intermediate filaments attaching to such dense bands . </P>

What is the structure of a smooth muscle cell