Describe calcium's role in the contraction of the sarcomere in skeletal and cardiac muscle tissues. Include the following in your answer : sarcomere, myosin, actin, myosin-binding sites, cross bridge, sarcoplasmic reticulum, ATP, ADP and Pi, troponin, tropomyosin, and Ca2+ channels
What will be an ideal response?
In skeletal and cardiac sarcomeres, tropomyosin covers up myosin-binding sites on actin. Ca2+ ions bind to troponin and cause it to move tropomyosin off the binding sites. Myosin cross bridges, which are bound with ADP and Pi, attach to the actin. The ADP and Pi then detach, causing the cross bridge to pull on the actin in a power stroke. At the end of the power stroke, ATP attaches to the cross bridge, causing it to detach from actin. The myosin then hydrolyzes the ATP to form ADP and Pi, causing the cross bridge to bend back and prepare for another power stroke. Ca2+ ions are stored inside the sarcoplasmic reticulum and are released when an impulse causes special Ca2+ channels to open. Cardiac muscle also receives some Ca2+ ions directly from the ECF through other Ca2+ channels.
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