For further discussion of muscle within the
context of the structures and functions of the
musculoskeletal system, please see the overview
section “The Musculoskeletal System.”
See also CELL STRUCTURE AND FUNCTION; FASCIA;
LIGAMENT; PROPRIOCEPTION; TENDON.
muscle relaxant medications Medications that
relieve MUSCLEspasms, cramps, and stiffness. Some
muscle relaxants are also called antispasmodic
medications. Doctors may prescribe these medica-
tions to treat acute BACK PAIN, acute sprains, severe
muscle tension HEADACHE, and muscle spasticity
due to conditions such as CEREBRAL PALSY, MULTIPLE
SCLEROSIS, SPINAL CORD INJURY, MUSCULAR DYSTROPHY,
FIBROMYALGIA, and many others. There are various
types of muscle relaxant medications that work
through different mechanisms, though all act on
the CENTRAL NERVOUS SYSTEM rather than on the
muscles directly. Because of this, most muscle
relaxants also affect alertness, balance, and other
neurologic functions.
As with any medication, muscle relaxants can
have adverse side effects and interact with other
drugs, including OVER-THE-COUNTER(OTC) DRUGSand
herbal remedies. Typically muscle relaxants pro-
vide short-term relief during acute injury. Once
muscle fibers begin to heal, they return to normal
contraction and relaxation patterns and muscle
relaxant medications are no longer necessary or
helpful for recovery. Muscle relaxants in the ben-
zodiazepine family of drugs (such as diazepam)
cause significant drowsiness and can become habit
forming; doctors generally prescribe them spar-
ingly because of these risks.
COMMON MUSCLE RELAXANT MEDICATIONS
carisoprodol chlorzoxazone
cyclobenzaprine diazepam
metaxalone methocarbamol
See also ADVERSE REACTION; CRAMP; DRUG INTERAC-
TION; MEDICINAL HERBS AND BOTANICALS; PHYSICAL
THERAPY; SPRAINS AND STRAINS; SPASM.
muscular dystrophy The collective term for a
group of GENETIC DISORDERSof the MUSCLEresulting
in progressive weakness. Most types of muscular
dystrophy arise from a deficiency of the protein
dystrophin, which is essential for skeletal (stri-
ated) muscle cell integrity and function. Without
it the skeletal muscles deteriorate and movement
becomes difficult or impossible. About 50,000
Americans have muscular dystrophy. The three
most common of the nine major types of muscular
dystrophy are Duchenne’s muscular dystrophy,
facioscapulohumeral muscular dystrophy, and
myotonic muscular dystrophy.
Duchenne’s muscular dystrophy Duchenne’s is
an X-linked recessive MUTATIONaffecting the dys-
trophin GENE. As such, it nearly exclusively affects
boys. Symptoms begin to appear in early child-
hood with characteristic postures and gait. Pro-
gression is steady, and most boys who have
Duchenne’s lose the ability to walk by about age- The skeletal muscles of the upper chest
become involved in ADOLESCENCE, affecting BREATH-
ING. Duchenne’s is usually fatal before age 20.
A milder presentation of similar symptoms and
pattern of progression with a later age of onset
(late childhood or early adolescence) is Becker’s
muscular dystrophy. Though the course of the dis-
ease is ultimately fatal, most who have it live into
their 30s. Treatment is primarily supportive, with
PHYSICAL THERAPYto help preserve muscle STRENGTH
and function. CORTICOSTEROID MEDICATIONS may
improve symptoms.
Facioscapulohumeral muscular dystrophy An
adult-onset type of muscular dystrophy, facio-
scapulohumeral muscular dystrophy affects men
and women equally. Symptoms first appear as
weakness in the muscles of the face and shoulder
girdle (upper arms and shoulders). The shoulders
often “wing” outward. Over the course of the dis-
ease, muscle weakness moves downward through
the body though the lower arms are usually the
last affected. Symptoms are mild enough in about
half of those who have this form of muscular dys-
trophy to permit fairly normal function and
mobility throughout life. In others, symptoms may
affect swallowing and mobility.
Myotonic muscular dystrophyIn myotonic mus-
cular dystrophy the muscles lose the ability to relax
after contraction, causing them to become stiff.
Myotonic muscular dystrophy is the most common
type of adult-onset muscular dystrophy and affects
men and women equally. The cause is a mutation
in the gene that encodes for myotonica protein
muscular dystrophy 337