MICROANATOMY

Detailed explanation-1: -A single muscle fiber contains hundreds to thousands of rod-like myofibrils that run parallel to its length (Figure 9.2b). The myofibrils, each 1–2 m in diameter, are so densely packed in the fiber that mitochondria and other organelles appear to be squeezed between them.

Detailed explanation-2: -Individual myofibrils (approximately 1 m in diameter) comprise approximately 80% of the volume of a whole muscle. The number of myofibrils ranges from 50 per myocyte in the muscles of a fetus to approximately 2000 per myocyte in the muscles of an untrained adult.

Detailed explanation-3: -Within each muscle fiber are myofibrils-long cylindrical structures that lie parallel to the muscle fiber. Myofibrils run the entire length of the muscle fiber, and because they are only approximately 1.2 µm in diameter, hundreds to thousands can be found inside one muscle fiber.

Detailed explanation-4: -Muscles are composed of long bundles of myocytes or muscle fibers. Myocytes contain thousands of myofibrils. Each myofibril is composed of numerous sarcomeres, the functional contracile region of a striated muscle.

Detailed explanation-5: -The connective tissue sheath covering each fasciculus is known as perimysium, and the innermost sheath surrounding individual muscle fiber is known as endomysium. [9] Each muscle fiber is comprised of a number of myofibrils containing multiple myofilaments.