The Muscular System 223
Common Disease, Disorder, or ConditionDisorders of Muscle continuedMyositis^
Myositis (my-oh-SIGH-tis) means inflammation of muscular tissue.
Atrophy^
Atrophy (AT-troh-fee) is a decrease in muscle bulk due to a lack of exercise, as when a
limb is in a cast for a prolonged period. Stimulation of nerves with a mild electric current
can keep muscular tissue viable until full muscular activity can return. In severe cases,
the muscle fibers are actually lost and replaced with connective tissue.
Hypertrophy^
Hypertrophy (high-PER-troh-fee) (the opposite of atrophy) is an increase in the size of
a muscle caused by an increase in the bulk of muscle cells through exercises, like
weightlifting. This activity increases the amount of protein within the muscle cell. We are
born with all the muscle cells we will ever have. They do not increase in numbers, only
in size.
Tendinitis^
Tendinitis (tin-den-EYE-tis) is an inflammation of a tendon.
Muscular Dystrophy^
Muscular dystrophy (MUSS-kew-lehr DIS-troh-fee) is an inherited muscular disorder,
occurring most often in males, in which the muscle tissue degenerates over time,
resulting in complete helplessness.
Myasthenia Gravis^
Myasthenia gravis (mye-as-THEE-nee-ah GRAV-is) is characterized by the easy tiring
of muscles, or muscle weakness. It usually begins in the facial muscles. It is caused by
the abnormal destruction of acetylcholine receptors at the neuromuscular junction. This
is an autoimmune disorder caused by antibodies that attack acetylcholine receptors.
Amyotrophic Lateral Sclerosis^
Amyotrophic lateral sclerosis (ALS) is also known as Lou Gehrig’s disease. It is a
progres-sively degenerative disease of the motor neurons of the body. It affects people
in middle age. Around 10% of the cases can be genetically inherited, the gene causing
the condition being on chromosome 21. The disease is caused by a degeneration of the
motor neurons of the anterior horns of the spinal cord and the corticospinal tracts. It
begins with muscle weakness and atrophy. It usually first involves the mus-cles of the
legs, forearm, and hands. It then spreads to involve muscles of the face, affecting
speech, and other muscles of the body. Within 2–5 years, there is a loss of muscle
control that can lead to death. There is no known cure for the disease. It also
sometimes is referred to as wasting palsy.
Rigor Mortis^
Rigor mortis occurs after death when muscles cannot contract (RIGOR 5 rigidity, MOR-TIS
5 of death). This occurs as calcium ions leak out of the sarcoplasmic reticulum and cause
contraction to occur. Since no ATP is being produced, the myosin cross-bridges