Cross Bridge Cycling
Storyboard Text
- Oh my! I've never quite seen a purple frog before.
- Well hello Mr. Frog! Tell me, how exactly do your legs move like that?
- Hello Alice. Welcome to Wonderland. Ya see, all skeletal muscles contract by filaments sliding against each other.
- What causes these filaments to slide?
- Well, when action potential sweeps along the sarcolemma, the muscle becomes excited. This causes the sacs of the sarcoplasmic reticulum to release calcium ions.
- Go on.
- Those calcium ions bind to regulatory proteins on thin filaments which exposes myosin-binding sites on the actin, allowing the myosin heads to attach to them. When those myosin heads attach, its called a Cross Bridge.
- So the sarcomere is the contractile unit?
- When myosin attaches to actin, Each cross bridge pivots in a rowing motion, causing the thin filaments to slide toward the center of the sarcomere.
- Yes! The cell shortens and contraction occurs. During this contraction, a Cross Bridge attaches and detaches several times.
- As you could assume, this takes a lot of energy. So ATP provides the energy for the sliding processes, which continues as long as calcium ions are present. ATP helps to to release and recock each myosin head.
- How neat!
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