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Q.
During contraction of muscles $Ca^{2+}$ binds to
Locomotion and Movement
Solution:
When action potential is generated in muscle fibre, it causes the release of $Ca^{++}$ from sarcoplasmic reticulum. Calcium binds with subunit of troponin (troponin - C) on actin filaments and activates it. Activated actin binds to the myosin head to form a cross bridge. This bridge pull the actin filaments causing them to slide over the myosin filaments and there by causing contraction.