1.) What is the role of sarcoplasmic reticulum,myosin head and F actin during contration of striated muscles of human beings???

2.) What is the role of Ca++ troponin during muscles contration?

Answer 1:

Sarcoplasmic reticulum: Sacroplasmic reticulum is a special type of endoplasmic reticulum found in muscle fibres. Its function is to store and control the release of calcium ions. When the muscle is contracting, its sarcoplasmic reticulum releases calcium ions and when it is relaxing, the calcium ions are absorbed back.

Myosin head and F actin: Myosin head binds to the F-actin filaments and together they result in the hydrolysis of ATP, to release energy required for the movement of actin filaments which result in contraction.

Answer 2:

Under relaxed conditions, the active site of actin fibres is protected by tropomyosin molecules. When the muscle fibres receive a signal, the sarcoplasmic reticulum gets activated and releases calcium ions. These calcium ions interact with the tropomyosin and result in a conformational change in troponins. This leads to a change in interaction between tropomyosin and actin fibres resulting in an exposed active site where myosin head can bind and initiate the contraction.