Disorders of the Muscular and Skeletal Systems

Because the muscular and skeletal systems work together as a single locomotor system, a disorder can arise in the muscle itself, at the neuromuscular junction where nerve meets muscle, in a joint, or in bone tissue, and in every case the outcome is felt as pain, weakness or restricted movement.

Myasthenia gravis is an autoimmune disorder in which the body's own immune system produces antibodies directed against the acetylcholine receptors present at the neuromuscular junction. Because acetylcholine, released from the nerve ending, can no longer act effectively on these receptors, transmission of the nerve signal to the muscle fibre is progressively impaired, causing increasing muscle fatigue and weakness with repeated use; in severe, untreated cases it can lead to paralysis of the muscles concerned, including the muscles of breathing.

Tetany is a condition of rapid, involuntary spasms (twitches) of skeletal muscle, and its immediate cause is a fall in the level of calcium in the body fluids below the normal range, since calcium is essential for the normal, controlled functioning of nerve and muscle tissue.

Muscular dystrophy refers to a group of disorders, mostly genetic in origin, in which skeletal muscle undergoes progressive degeneration over time; the muscle fibres are gradually damaged and replaced by connective and fatty tissue, leading to increasing muscle weakness. Duchenne muscular dystrophy is the most well-known and most severe example.

Arthritis is inflammation of one or more joints, and it can arise from more than one underlying cause: rheumatoid arthritis is an autoimmune condition in which the body's own immune system attacks the tissue lining the joints, osteoarthritis is the wear-and-tear degeneration of joint cartilage that becomes more common with age, and gouty arthritis (see gout, below) results from the deposition of uric acid crystals within a joint. In every form, the affected joint becomes painful, swollen and stiff, and movement at that joint is restricted. …