The skeleto-muscular unit (figure 5-5) is a working concept of muscle and skeleton producing motion. The components of an S-M unit are bones, a joint, and skeletal muscle(s).
a. Bones. Bones act as levers and as attachment sites for skeletal muscles.
b. Joint (Articulation). The joint is the center, fulcrum, point, or axis of motion.
c. Skeletal Muscle(s). Skeletal muscles apply the forces for motion. Any given motion utilizes a group of muscles working together. A skeletal muscle may serve only one of the three following major roles during a particular motion:
(1) Prime mover. The muscle which makes the main effort for a given motion is called the prime mover, or agonist.
(2) Synergist. A synergist is a muscle which assists the prime mover.
SYN = together ERG = unit of effort
(3) Antagonist. An antagonist applies a force opposite to that of the prime mover.
(a) By opposing the prime mover, the antagonist helps control the
(b) The antagonist also brings the limb or other part back to its original
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