What is skeletal muscle?
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Skeletal muscle is made up of very specialized cells that have the ability to shorten when they are stimulated. With the exception of reflex mechanisms, such as the knee tap by a physician, movement of our skeletal muscle is under the command of our brain, as mentioned earlier. Because muscle cells are very long they are often referred to as muscle fibers (see Skeletal Muscle Figure). The fibers are bundled up like a box of dry spaghetti or straight wires in a cable. The muscle fiber bundles are themselves bundled up and are part of larger collection of similar bundles which make up a particular muscle. Skeletal muscle is so named because it is generally anchored at both ends to different bones of our skeleton. When muscle contracts, it pulls on a specific bone, which moves the bone, thus moving a body part. |
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How does skeletal muscle work?
Like neurons, skeletal muscle fibers are also excitable. In fact, the excitability process of muscle cells is very similar to that of neurons, while the end result is different. Excitability in muscle fibers leads to the contraction of the muscle cell while neurons merely carry the electrical nerve impulse to another neuron or to skeletal muscle or other tissue and organs.
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The inside of skeletal muscle fibers appears very different from other cells because of the contractile apparatus it contains. Each muscle fiber contains a tremendous amount of small fibrous units called myofibrils, as shown in Sarcomere Figureand Sarcomere Contraction. The prefix myo refers to muscle and fibril means little fiber. Each myofibril is a stalk-like collection of proteins. The predominant proteins are actin and myosin, which are referred to as the thin and thick filaments, respectively. They are organized into a series of tiny contraction regions called a sarcomere. Myofibrils are composed of thousands of sarcomeres situated side by side. |
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