MICROANATOMY

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: -Calcium triggers contraction in striated muscle. (A) Actomyosin in striated muscle. (1) Striated muscle in the relaxed state has tropomyosin covering myosin-binding sites on actin. (2) Calcium binds to troponin C, which induces a conformational change in the troponin complex.

Detailed explanation-3: -Calcium diffusing in the cytoplasm between myosin and actin filaments of the muscle fibrils causes the filaments to slide into each other, triggering the contraction of the entire muscle fiber.

Detailed explanation-4: -The correct answer: The role of calcium ions in muscle contraction is to C) bind to regulatory sites on troponin, changing the configuration. The importance of calcium ions is there in the muscle contraction because it acts as the ion which helps in the movement of the troponin.