b. Sesamoid bones, such as the patella (kneecap), develop in tendons where
pressure is applied to the tendon.
5-8. THE SKELETO-MUSCULAR UNIT
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
Figure 5-5. The skeleto-muscular unit (arm-forearm flexion
(3rd class lever system)).
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