of stairs, hurry to catch a bus, or just go dancing, you
might reflect a moment on all of the things that are
actually happening to your body... after you catch
your breath.
AGING AND THE
MUSCULAR SYSTEM
With age, muscle cells die and are replaced by fibrous
connective tissue or by fat. Regular exercise, however,
delays atrophy of muscles. Although muscles become
slower to contract and their maximal strength de-
creases, exercise can maintain muscle functioning at a
level that meets whatever a person needs for daily
activities. The lifting of small weights is recom-
mended as exercise for elderly people, women as well
as men. Such exercise also benefits the cardiovascular,
respiratory, and skeletal systems.
The loss of muscle fibers also contributes to a loss
of proprioception, because the brain is getting less
information about where and how the body is posi-
tioned. The loss of muscle sense contributes to
unsteadiness in elderly people and to an impaired
sense of balance, which in turn may lead to a fall.
Simple awareness of this may help an elderly person
prevent such accidents.
MAJOR MUSCLES OF THE BODY
The actions that muscles perform are listed in Table
7–2 and some are shown in Fig. 7–7. Most are in pairs
as antagonistic functions.
After the brief summaries of the muscles of each
body area that follow, the major muscles are shown in
Fig. 7–8. They are listed, according to body area, in
Tables 7–3 through 7–7, with associated Figs. 7–9
through 7–13, respectively. When you study the dia-
grams of these muscles, and the tables that accompany
them, keep in mind the types of joints formed by the
bones of their origins and insertions. Muscles pull
bones to produce movement, and if you can remember
the joints involved, you can easily learn the locations
and actions of the muscles.
The name of the muscle may also be helpful, and
again, many of the terms are ones you have already
learned. Some examples: “abdominis” refers to an
abdominal muscle, “femoris” to a thigh muscle,
“brachii” to a muscle of the upper arm, “oculi” to an
The Muscular System 149eye muscle, and so on. Other parts of muscle names
may be words such as “longus” or “maximus” that
tell you about size, or “flexor” that tells you about
function.
Muscles that are sites for intramuscular injections
are shown in Box 7–5.BOX7–5 COMMON INJECTION SITES
Intramuscular injectionsare used when rapid
absorption is needed, because muscle has a
good blood supply. Common sites are the but-
tock (gluteus medius), the lateral thigh (vastus lat-
eralis), and the shoulder (deltoid). These sites are
shown; also shown are the large nerves to be
avoided when giving such injections.Box Figure 7–A Sites for intramuscular injections.
Posterior view of right side of body.