Contact is maintained by the binding of the extracellular domain of a transmemebrane receptor protein called integrin to extra cellular matrix proteins. The intracellular domain of integrin binds to a complex of proteins including actin cytoskeletal components to form a focal adhesion . The migration of animal cells can be divided into three actin-dependent subprocesses. 16-80 Model of cell motility Muscle Bulk of the cytoplasm in muscle fibers consist of myofibril s, the contractile elements of the muscle cell. Each myofibril consists of tiny contractile units called sarcomeres, made up of thin actin filaments and thick myosin filaments.
Muscle contraction is produced by the sliding of actin filaments against myosin filaments.
16-89 Sarcomere Troponin and tropomyosin allow the contraction of skeletal and cardiac muscle to be regulated by calcium. In both skeletal and non muscle cells, the activity of myosins are mediated by calcium-regulated phosphorylation of myosin light chain.