What stops a muscle contraction- ATP or calcium ions?

[virtualmaster999]

Hey everyone quick question on the muscular system. So I have one book that says that calcium going back into the sarcoplasmic reticulum stop contraction and another that says that if new atp isn't present, the muscle stays contracted, and isn't released. So is it both?

Please let me know! Thank you!


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[LaughingGas]

Both

 

[torontopharm]

Both are right i believe.
You want Ca2+ to go out from sarcoplasmic reticulum to the cytoplasm where the actin and myosin are, so Ca2+ can bind to troponinC on tropomyosin and remove it out of the way for contraction to happen.
Without new ATP binding to the myosin, myosin will remain attached to actin, so you'll get rigor mortis and you remain contracted.

Someone correct me if i'm wrong