HUMAN BIOLOGY

114 Chapter 6

Diseases and Disorders of the muscular system

which is needed for the proper transmission of nerve

impulses to muscles and other tissues. Gentle stretching

and massage may coax a cramped muscle to release.

Most people experience occasional muscle “tics.” These

minor, involuntary twitches are common in muscles of

the face and eyelids and may be triggered by anxiety or

some other psycho-emotional cause.

muscular dystrophies destroy

muscle fibers

Muscular dystrophies are part of a large group of

genetic diseases in which skeletal muscle fibers break

down. Whole muscles in turn weaken and shrivel.

If you have ever torn a muscle or known someone with a

muscle-wasting disease, you are well aware that any prob-

lem that impairs the ability of skeletal muscles to produce

movement has a serious impact on activities that most of

us take for granted. The general medical term for a muscle

disorder, “myopathy,” means muscle disease. In general,

ills that can befall our skeletal muscles fall into three cat-

egories: injuries, disease, and disuse.

muscle injuries include strains and tears

Given that our muscular system gets almost constant use,

it’s not surprising that the most common disorders of skel-

etal muscles are injuries. Lots of people, and athletes espe-

cially, strain a muscle at some point in their lives (Figure

6.16). The injury happens when a movement stretches or

tears muscle fibers. Usually, there is some bleeding into the

damaged area, which causes swelling and a painful muscle

spasm. The usual first aid is an ice pack, followed by rest-

ing the affected muscle and using anti-inflammatory drugs

such as ibuprofen.

When a whole muscle is torn, the aftereffects can last a

lifetime. If scar tissue develops while the tear mends, the

healed muscle may be shorter than before. As a result, it

may not function as effectively.

Cramps and spasms are

abnormal contractions

In a muscle spasm, a muscle suddenly and involuntarily

contracts. A muscle cramp is a painful muscle spasm

that doesn’t immediately release. Any skeletal muscle can

cramp, but the usual “victims” are calf and thigh muscles.

In some cases the real culprit is a deficiency of potassium,

Figure 6.16 For athletes, muscle strains and tears often are “part of the game.”

© Maxisport/Shutterstock.com

Figure 6.17 Muscular dystrophies are inherited disorders.

Duchenne muscular dystrophy is most common in boys. Above,

the top image shows healthy muscle fibers. The lower image

shows muscle from a DMD patient. The fibers are misshapen

and have other characteristics used to diagnose the disease.

healthy muscle

DMD muscle

University of Melbourne

6.7

Russ Schleipman/Corbis

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