Skeletal Muscle Anatomy
The skeletal muscles, which are attached to the bony framework of the body (called the skeleton), control voluntary movements, such as walking, reaching, and talking. Every time the body moves, a skeletal muscle contracts.
Depending on where they are located and how they function, skeletal muscles vary considerably in size and shape, but they are all made up of bundles of fibers. Each muscle fiber is made up of a sophisticated system of sliding filaments that, when "told" what do by the brain via the nervous system, cause contraction and movement. The nerves that command the muscle are called motorneurons, and the place where a motorneuron meets the muscle is called the neuromuscular junction.
Motorneurons communicate with muscles by secreting biochemical substances. The skeletal muscles receive biochemical energy and transform it into mechanical energy that causes muscles to contract and the body to move.
When muscles are affected by disease (myopathy), many changes occur. These changes can lead to weakness, pain, and atrophy. In some cases, the muscle fibers are destroyed or undergo significant shrinkage (atrophy). In inflammatory myopathies, white blood cells and other blood elements attack parts of the muscle and surrounding blood vessels and scar tissue often takes the place of normal muscle tissue. In metabolic myopathies, abnormal amounts of biochemical substances may accumulate in the muscles.