Labs / Biology
Sliding Filaments
Tap the muscle to fire a nerve signal — calcium floods in, uncovering the binding sites so myosin heads can grab the actin and ratchet it inward. Each stroke burns ATP and the whole sarcomere visibly shortens. Fire faster and the individual twitches fuse into a smooth, powerful tetanus.
length 2.20 µmtension 0%Ca²⁺ 0%ATP 0
What to try
- Set “Twitch” and tap once. How long does the tension last after a single calcium pulse, and why does it fade?
- Slide the frequency up from 10 to 50 Hz. At what point do the separate twitches stop dipping back down and fuse into steady tetanus?
- Drag ATP toward 0 while stimulating hard. Why does the sarcomere stop sliding even though calcium is still high?
- Watch the ATP counter climb. Does holding a strong tetanus cost more fuel than the same muscle at rest?
- Compare the calcium trace with the tension trace. Which one rises first, and what does that lag tell you about how the signal becomes force?