NEET BIOLOGY

Detailed explanation-1: -Both calcium & magnesium are required for muscle contraction. Calcium binds to troponin which exposes the active sites on actin. Now myosin head can bind the active sites on actin, initiating the process of muscle contraction. The hydrolysis of ATP is used to provide energy for muscle contraction.

Detailed explanation-2: -Mg2+ plays a central role in the excitation-contraction (E-C) coupling of skeletal and cardiac muscle fibres of vertebrates.

Detailed explanation-3: -During contraction and relaxation, Ca2+ in the cytosol has a critical role in activating and deactivating a series of contractile proteins. In skeletal muscle, the cytosolic Ca2+ level is mainly determined by Ca2+ movements between the cytosol and the sarcoplasmic reticulum.

Detailed explanation-4: -Calcium triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin. Two different regulatory systems are found in different muscles.