how is muscle contraction stimulated by calcium ions? i. calcium ions are released from the sarcoplasmic reticulum and bind to myosin, stimulating atpase activity. ii. none of the other options. iii. calcium ions are released from the sarcoplasmic reticulum and bind to tropomyosin, stimulating its atpase activity. iv. calcium ions are released from the sarcoplasmic reticulum and bind to troponin c, promoting the binding of myosin to actin. v. calcium ions are released from the sarcoplasmic reticulum and bind to actin, promoting its binding to myosin.