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The sliding filament mechanism as explained by my text does not elaborate on how ATP is involved in the cross bridge binding and contraction process. How does muscle contraction utilize ATP?

In my text explains this is the procedure for a contraction:

  1. Ach released by motor neuron cross cleft and binds to motor end plate
  2. AP generated in response to binding of Ach gated channels and propagates down T tuble
  3. T tuble triggers Ca2+ from sarcoplasmic reticulum
  4. Ca2+ binds onto tropinin on actin filament and removes tropomyosin
  5. This opens up sites for myosin to attach to actin using protein heads
  6. Actin filament is pulled toward the center of sarcomere, causing contraction

I see that the action potential definitely needs ATP in order to be generated, aside from that I am surprised that the actual contraction via cross bridge binding does not seem to need ATP.

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    $\begingroup$ Step 6 requires ATP. $\endgroup$ – canadianer Apr 13 '15 at 21:57
  • $\begingroup$ Pumping Ca2+ back into the sarcoplasmic reticulum also requires ATP. $\endgroup$ – canadianer Apr 13 '15 at 22:02
  • $\begingroup$ It is used in the movement of the actin filament. youtube.com/watch?v=H6okUPuyby0 $\endgroup$ – Ansjovis86 May 9 '15 at 10:51
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ATP prepares myosin for binding with actin by moving it to a higher-energy state and a "cocked" position.

Once the myosin forms a cross-bridge with actin, the Pi disassociates and the myosin undergoes the power stroke, reaching a lower energy state when the sarcomere shortens.

ATP must bind to myosin to break the cross-bridge and enable the myosin to rebind to actin at the next muscle contraction.

enter image description here

The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin. As soon as the actin-binding sites are uncovered, the high-energy myosin head bridges the gap, forming a cross-bridge. Once myosin binds to the actin, the Pi is released, and the myosin undergoes a conformational change to a lower energy state. As myosin expends the energy, it moves through the "power stroke," pulling the actin filament toward the M-line. When the actin is pulled approximately 10 nm toward the M-line, the sarcomere shortens and the muscle contracts. At the end of the power stroke, the myosin is in a low-energy position.

After the power stroke, ADP is released, but the cross-bridge formed is still in place. ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site. ATP can then attach to myosin, which allows the cross-bridge cycle to start again; further muscle contraction can occur. Therefore, without ATP, muscles would remain in their contracted state, rather than their relaxed state.

Summary from: https://www.boundless.com/biology/textbooks/boundless-biology-textbook/the-musculoskeletal-system-38/muscle-contraction-and-locomotion-218/atp-and-muscle-contraction-826-12069/

Also this:

Essentially look up the cross bridge cycle (http://muscle.ucsd.edu/musintro/bridge.shtml)

I would also suggest reading it from the master himself here: Huxley, A. F. "Muscular contraction." The Journal of physiology 243.1 (1974): 1-43.

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  • $\begingroup$ It begs the question what the mechanism of bending of the myosin head during the power stroke is . Is there any reference for this? $\endgroup$ – Hans Sep 11 '16 at 9:14

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