Question

Describe in detail fine structure of striated muscle fibre.

Answer 1

Striated muscles that attach and move, the skeleton are called skeletal muscles. A skeletal muscle is composed of cells called muscle fibers which run in parallel along the entire length of the muscle. Each muscle fiber consists of a bundle of myofibrils. The cell membrane of a muscle fiber is called the sarcolemma. The cytoplasm is called the sarcoplasm. The endoplasmic reticulum is called the sarcoplasmic reticulum. Muscle fibers have multiple nuclei and numerous mitochondria. Muscle fibers have T-tubules that spread impulses. A myofibril is made up of units called sarcomeres. Sarcomeres line up end-to-end along the length of a myofibril.

A sarcomere is contained within two Z lines. A sarcomere contains many protein filaments, in a parallel array. Some filaments are thin (actin), and the others are thick (myosin). The orderly array of actin and myosin filaments in the sarcomeres gives skeletal muscles a striated appearance (light and dark bands). Myosin molecules have long tails and two round heads. The tails are packed together in parallel and the heads stick out to the sides. Actin is a globular protein that forms two beaded strands, twisted together. Actin filaments also have the proteins, tropomyosin and troponin. Tropomyosin is a long thin molecule that wraps around the actin filament. Troponin is a globular protein situated at regular intervals along the tropomyosin.