Muscle Sarcomere Contraction

Muscle Sarcomere Contraction 3D demonstrates the sliding filament mechanism of skeletal muscle physiology. Framed between two blue Z-disc plates, thin green actin filaments overlap a central thick red myosin filament studded with hinged myosin heads. Students can drag either Z-disc horizontally or click the myosin heads to trigger a calcium release pulse. Sliders for Calcium (Ca2+), ATP concentration, and external Load force allow students to observe active cross-bridge cycling, measure sarcomere shortening from 2.5 micrometers down to 1.6 micrometers, and see why depleting ATP locks cross-bridges in the rigor state.

• Drag the left or right cyan Z-disc plate inward to see how thin actin filaments slide past the central thick myosin filament without either filament changing length.
• Lower Calcium release to 0% and see how tropomyosin blocks actin so myosin heads cannot attach and muscle tension drops to zero.
• Raise both Calcium and ATP above 80% to watch the hinged myosin heads ratchet back and forth in the cross-bridge power stroke.
• Set Calcium to 80% and drop ATP concentration to 0% to demonstrate rigor mortis, where myosin heads stay locked onto actin unable to detach.

1. 1Identify the Z-discs, M-line, thin actin filaments, and thick myosin filaments of a skeletal muscle sarcomere.
2. 2Explain how Ca2+ binding to troponin shifts tropomyosin to expose myosin-binding sites on actin.
3. 3Describe the four steps of the cross-bridge cycle: attachment, power stroke, ATP-driven detachment, and ATP hydrolysis recocking.
4. 4Explain why sarcomere length shortens during muscle contraction while the individual myofilaments stay the same length.

Questions teachers ask