Final answer:
The skeletal muscle's structure begins macroscopically with a protective sheath called epimysium and moves inward to perimysium-wrapped fascicles, to endomysium-encased muscle fibers, which contain myofibrils. These myofibrils are made up of sarcomeres with actin and myosin filaments that give muscles their striated look.
Step-by-step explanation:
Skeletal Muscle Anatomy: Macroscopic to Microscopic
The skeletal muscle is a complex organ composed of various tissues including muscle fibers, blood vessels, nerve fibers, and connective tissue layers which provide structure and facilitate the muscle's function. At the macroscopic level, the outermost layer of connective tissue surrounding the entire muscle is called the epimysium. This dense layer supports the muscle during powerful contractions and separates it from surrounding tissues.
Deeper within, muscles are divided into bundles called fascicles, each surrounded by the perimysium. Contained within each fascicle are numerous muscle fibers, which are long, cylindrical cells. Each individual muscle fiber is wrapped in a connective tissue layer called the endomysium.
Microscopically, muscle fibers contain myofibrils, which are composed of repeating units called sarcomeres. These sarcomeres are the contractile units and are stacked in a linear array within each myofibril. Sarcomeres, in turn, are made up of thin (actin) and thick (myosin) myofilaments arranged in a pattern that gives the muscle its striated appearance.