ANATOMY

Detailed explanation-1: -The sarcoplasmic reticulum of the muscle fibers stores calcium ions. Myofilaments or myofibrils are parallelly arranged filaments present in the sarcoplasm having alternate dark and light bands. Myofibrils have striated appearance due to the distribution of two important proteins – Actin and Myosin.

Detailed explanation-2: -The arrangement of the thick myosin filaments across the myofibrils and the cell causes them to refract light and produce a dark band known as the A Band. In between the A bands is a light area where there are no thick myofilaments, only thin actin filaments.

Detailed explanation-3: –The dark band is known as ‘A’ or Anisotropic band which carries Myosin whereas the light bands which carry actin and are called I-band or Isotropic band. Hence called striped muscles thanks to the presence of striations.-Hence Myofibrils show dark and lightweight bands in Cardiac muscles and striated muscles.

Detailed explanation-4: -The A band is comprised of thick filaments consisting primarily of the protein myosin. The two half-I bands at either side of the A bands contain thin filaments, which extend into the A band in the center of the sarcomere from their origin at the Z lines.

Detailed explanation-5: -Within a muscle fiber, proteins are organized into organelles called myofibrils that run the length of the cell and contain sarcomeres connected in series. Because myofibrils are only approximately 1.2 m in diameter, hundreds to thousands (each with thousands of sarcomeres) can be found inside one muscle fiber.