1. Sliding Filament Theory How do muscles work…..

2. Muscle Cell Structure n Muscles are broken into smaller muscle fibers n muscle fibers are broken into smaller units called myofibrils n myofibrils are broken into smaller units called sarcomeres

3. Sarcomere Structure - units of muscle contraction n These are made up of alternating thick proteins filaments (myosin) and thin protein filaments (actin) n This pattern forms different zones as shown here

4. Close up look at Myosin & Actin n Myosin filaments contain “heads” n Actin filaments contain binding sites n ATP is necessary for the contraction to occur

5. “Power Strokes” n Actin filaments slide towards the center of sarcomere when muscle contracts….. Away when it relaxes n Myosin heads attach to binding sites forming cross bridges n when activated the cross bridges tilt inward towards center in a short powerful stroke

6. Muscle Contraction n ATP is required for the “heads” to detach and move to the next binding site n A series of power strokes causes noticeable muscle contraction n with no ATP the myosin heads do not detach and RIGOR occurs