Summary

Summary

Skeletal muscles primarily function in groups and are differentiated into prime movers (agonists), synergists, and antagonists. One end of a skeletal muscle is usually fastened to a mostly immovable section called an origin at a movable joint. Its other end connects to a movable section called an insertion located on the other side of the joint. Muscle contraction produces certain actions or movements. A muscle’s “head” is the part closest to its origin. When joint angles are decreased, flexion occurs, and when joint angles are increased, extension occurs. Muscle injuries are assessed via manual muscle testing. Muscles are then graded in numbers ranging from zero to five, with five indicating normal function and zero indicating no muscle activity.

Skeletal muscles are mostly classified as parallel muscles, in which fascicles are parallel to the long axes. They are also classified as convergent (extend-ing over a broad area with a single attachment site), pennate (creating a common angle with the ten-don, with fibers pulling at an angle), and circular (arranged around a body opening in a concentric pattern). Range of motion and muscle strength is based on how the fascicles are arranged, with par-allel fascicles offering the most ability to shorten but less strength. Muscles may be named based on their location, shape, size, fiber direction, number of origins, attachment locations, and actions. Most skeletal muscles use leverage to move, with the bones acting as levers and the joints acting as fulcrums. They either operate at a mechanical advantage, which offers more power, or at a mechanical disadvantage, which offers more speed and range of motion. Our muscular system reaches its maximum ability by age 25, but begins to deteriorate by age 40.