Question

What are the roles of $C{a}^{++}$ and ATP in muscle contraction?

Answer 1

When a muscle fiber is relaxed, the concentration of calcium ions is less in the sarcoplasm. As a muscle action potential travels along the sarcolemma and into the transverse tubule system, the ions release channels open in the sarcoplasmic reticulum membrane. As a result calcium ions flood in the sarcoplasm around the thick and thin filaments which in turn binds troponin (muscle protein) that causes the change in shape.

The globular head of myosin acts as an ATPase enzyme that hydrolyzes ATP molecule. The energy derived from the hydrolysis of ATP is used by myosin to bind to the exposed active site on the actin filament to form a cross bridge.