Muscular System

Disorders of the muscular system can be due to genetic, hormonal, infectious, autoimmune, poisonous, or cancerous causes. But the most common problem associated with this system is injury from misuse. Skeletal muscle sprains and tears cause excess blood to seep into the tissue in order to heal it. The remaining scar tissue leads to a slightly shorter muscle. Muscular impairment and cramping can result from a diminished blood supply. Cramping can be due to overexertion. Poor blood supply to the heart muscle causes chest pain called angina pectoris. And inadequate ionic supplies of calcium, sodium, or potassium can adversely effect most muscle cells.

Muscular system disorders related to the immune system include myasthenia gravis (MG) and tumors. MG is characterized by weak and easily fatigued skeletal muscles, one of the symptoms of which is droopy eyelids. MG is caused by antibodies that a person makes against their own Ach receptors; hence, MG is an autoimmune disease. The antibodies disturb normal Ach stimulation to contract skeletal muscles. Failure of the immune system to destroy cancerous cells in muscle can result in muscle tumors. Benign muscle tumors are called myomas; while malignant muscle tumors are called myosarcomas.

Contamination of muscle cells by infectious substances and drugs can also lead to muscular disorders. A Clostridium bacteria can cause muscle tetanus, which is a disease characterized by painful repeated muscular contractions. In addition, some types of gangrene are due to bacterial infections deep in a muscle. Gangrene is the decay of muscle tissue in varying degrees; it can involve small areas of a single muscle or entire organs. The poisonous substance, curare, blocks neuromuscular transmission in skeletal muscle causing paralysis. And large doses of prolonged alcohol consumption can cause muscle damage, as well.

The most common type of muscular genetic disorder is muscular dystrophy of which there are several kinds. Duchenne's muscular dystrophy is characterized by increasing muscular weakness and eventual death. Becker's muscular dystrophy is milder than Duchenne's, but both are X-linked recessive genetic disorders. Other types of muscular dystrophy are caused by a mutation that affects the muscle protein dystrophin, which is absent in Duchenne's and altered in Becker's muscular dystrophies. Other genetic disorders (such as some cardiomyopathies) can affect various muscle tissues.