Bundle of fibers Muscle fiber (muscle cell) Myofibril Sarcomere
Myosin filamentActin filament Relaxed Partially contracted Fully contracted Z- line M- disk A band H Zone
Myofibril I band A band H Zone Z line One Complete Sarcomere M line
ActinTroponinTropomyosin Thin filament organization
Myosin Tail ( -helix coiled coil) Myosin Head Myosin light chains (LC1, LC2)
M-disk Region
ATP binding causes release of myosin from actin ATP
Hydrolysis of ATP ADP Pi Conformational change “cocking of myosin head”
ADP Pi Formation of myosin/actin crossbridge
“Power Stroke” ADP Pi Release of ADP and Pi
High Ca 2+ Ca 2+ channel Ca 2+ pump Ca 2+ / calmodulin MLCK MLCK-Ca 2+ (active) Myosin/MLC (relaxed) Myosin/MLC- P (contraction) ATPADP PiH2OH2O MLC phosphatase MLCK- P (inactive) MLCK phosphatase Epinephrine receptor Epinephrine G Protein Adenylate cyclase ATP cAMPR 2 C 2 Protein kinase (inactive) 2C Protein kinase (active) Electrical stimulation Monocyte membrane