Sliding Filament Cross-Section (2D)

This 2D companion strips the sarcomere down to a flat, labeled cross-section so the sliding filament mechanism is easy to follow: myosin cross-bridge heads cock, grab the neighboring actin filament, and row it toward the M-line in a power stroke, then release and re-cock to repeat the cycle. Raise the calcium level and hit Stimulate to expose actin's binding sites and watch the sarcomere shorten as the heads pull the filaments inward; lower ATP availability and the heads cycle more slowly, and at near-zero ATP they seize mid-stroke, locked onto actin — the same rigor that causes rigor mortis. Live readouts track sarcomere length, contraction force, and how fast the cross-bridges are cycling.