Calcium plays an important biochemical role as a trigger for muscle contraction. In the state of rest, the levels of calcium near the muscle fibres are very low since almost all the calium ions in muscle are pumped into a complex network of vehicles called sarcoplasmic reticulum or SR. The calcium ion trigger muscle contraction. Two different regulatory systems are found in different muscles. In actin- linked regulation troponin and tropomyosin regulate actin by blocking sites on actin required for conplex formation with myosin ; In myosin- linked regulation sites on myosin are blocked in the absence of calcium. Many invertebrates have muscles with both types of regulation.
Nerve impulses induce the SR membrane to release large amounts of calcium quickly. Calcium is the intermediary between the nerve impulse and muscle contraction. Relaxation of the muscle demands reduction in calium level to their level of rest. This is accompained by an ATP- driven calcium transport protein called calium -ATPase. Calcium ATPase is an integral part of calcium pump just as Na+ - K+ ATPase is an integral part of Na+ - K+ pump. The calcium ATPase is transcently phosphorylated by ATPase is the case with Na+ -K+ pump. Thus we can say calcium plays an important biochemical /biological role as a trigger for muscle contraction.
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