Disorders of Muscular and Skeletal System

The muscles and the skeleton keep us upright and let us move, but both systems can be affected by a range of disorders. Some of these arise from faults in the way nerves signal muscles, some from inherited defects, some from a shortage of a particular ion or hormone, and others from long-term wear or the build-up of harmful substances in the joints. The common conditions grouped under this heading are described below.

Disorders that mainly affect muscle

• Myasthenia gravis — This is an auto-immune disorder, meaning the body's own defence system mistakenly attacks its own tissues. Here the attack is directed at the neuromuscular junction, the point where a nerve passes its command on to a skeletal muscle fibre. Because the signal can no longer be handed over properly, the muscle tires very quickly, grows weak, and in severe cases becomes paralysed. The weakness and fatigue affect the skeletal (voluntary) muscles.

• Muscular dystrophy — This refers to a steady, progressive wasting away of the skeletal muscles. The muscle tissue degenerates over time, so the affected muscles gradually lose their strength and bulk. It is caused mostly by a genetic (inherited) defect, which is why it tends to run in families.

• Tetany — When calcium-ion levels in the body fluids drop below what the muscles need, the muscle fibres start twitching and clamping down on their own, uncontrollably -- a runaway series of jerks and cramps that together are called tetany. The trigger here is the calcium shortage itself, not any damage to the muscle tissue.

Disorders that mainly affect the joints and bones

• Arthritis — This is an inflammation of the joints. The affected joints become sore and swollen, which makes moving them painful and difficult. …