1. Bundle of fibers Muscle fiber (muscle cell) Myofibril Sarcomere

2. Myosin filamentActin filament Relaxed Partially contracted Fully contracted Z- line M- disk A band H Zone

3. Myofibril I band A band H Zone Z line One Complete Sarcomere M line

4. ActinTroponinTropomyosin Thin filament organization

5. Myosin Tail (  -helix coiled coil) Myosin Head Myosin light chains (LC1, LC2)

6. M-disk Region

8. ATP binding causes release of myosin from actin ATP

9. Hydrolysis of ATP ADP Pi Conformational change “cocking of myosin head”

10. ADP Pi Formation of myosin/actin crossbridge

11. “Power Stroke” ADP Pi Release of ADP and Pi

12. 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