Biomedical Engineering Reference
In-Depth Information
STERNOCLEIDOMASTOID
TRAPEZIUS
PECTORALIS
MAJOR
DELTOID
SERRATUS
ANTERIOR
BICEPS
BRACHII
ANTERIOR
FOREARM
MUSCLES
EXTERNAL
ABDOMINAL
OBLIQUE
TENSOR
FASCIAE
LATTAE
QUADRICEPS FEMORIS
VASTUS LATERALIS
SARTORIUS
RECTUS FEMORIS
VASTUS MEDIALIS
PATELLAR LIGAMENT
GASTROCNEMIUS
TIBIALIS ANTERIOR
SOLEUS
FIGURE 3.35
Some of the major skeletal muscles on the anterior side of the body.
mover are called antagonists, whereas muscles that assist a prime mover in producing a
movement are called synergists. The continual contraction of some skeletal muscles helps
maintain the body's posture. If all of these muscles relax, which happens when a person
faints, the person collapses.
A system of levers, which consists of rigid lever arms that pivot around fixed points,
is used to move skeletal muscle (Figure 3.36). Two different forces act on every lever:
the weight to be moved—that is, the resistance to be overcome—and the pull or effort
applied—that is, the applied force. Bones act as lever arms, and joints provide a fulcrum.
The resistance to be overcome is the weight of the body part that is moved, and the applied
force is generated by the contraction of a muscle or muscles at the insertion, the point of
attachment of a muscle to the bone it moves. An example of a first-class lever, one in which
the fulcrum is between the force and the weight, is the movement of the facial portion of the
head when the face is tilted upward. The fulcrum is formed by the joint between the atlas
and the occipital bone of the skull, and the vertebral muscles inserted at the back of
the head generate the applied force that moves the weight, the facial portion of the head.
A second-class lever is one in which the weight is between the force and the fulcrum. This
can be found in the body when a person stands on “tip toe.” The ball of the foot is the
fulcrum, and the applied force is generated by the calf muscles on the back of the leg.
The weight that is moved is that of the whole body. A third-class lever is one in which
the force is between the weight and the fulcrum. When a person has a bent elbow and holds
