The Structure of Skeletal Muscle

<h1>Text Preview</h1> <p>Each time we make the parts of our body move, skeletal muscles are contracting. Skeletal muscle is the type of muscle responsible for the voluntary movements of the body. To understand how skeletal muscle contracts, we need to first look at its structure. A skeletal muscle, like your biceps, is a bundle of muscle fibers running the length of the muscle. This pattern makes the muscle appear striped, or striated, so skeletal muscle is a type of striated muscle.</p> <p>Each fiber is actually a single cell with many nuclei. Each multinucleated cell contains a bundle of small, thin fibers called myofibrils. Each myofibril is made up of two types of threadlike myofilaments: thick and thin. A thick filament is composed of a staggered array of myosin proteins, each with a globular head and a long tail. A thin filament consists of two strands of the protein actin and one strand of tropomyosin, a regulatory protein.</p> <p>The arrangement of the myofilaments creates a repeating functional unit called a sarcomere. Each region of the sarcomere has a specific name. The borders on each side of a sarcomere are called Z lines. Only thin filaments attach to the Z lines. Between two thin filaments is a thick filament, centered within the sarcomere. The length of the thick filament is called the A band.</p> <p>When the muscle is at rest, the thick and thin filaments don't overlap completely. Next to the Z lines is a region where there are only thin filaments, called the I band. The center of the sacromere where there is only thick filament is called the H zone. We'll see in a moment how the structure of the sarcomere is the key to muscle contraction.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>