Cramp
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A cramp is an unpleasant sensation caused by contraction, usually of a muscle. It can be caused by cold or overexertion. Illness or poisoning can also cause cramps, particularly in the stomach, which is referred to as colic if it fits particular characteristics.
Menstruation also is highly likely to cause cramps of varying severity in the abdomen. Most of this is attributable to the passing of coagulated blood through the cervix.
Electrolyte disturbance may cause cramping and tetany of muscles, particularly hypokalemia (a lack of potassium) and hypocalcemia (a lack of calcium).
Smooth muscle
Smooth muscle contractions lay at the heart of the cramping of internal organs, such as the intestine, uterus and various others.
Skeletal muscle
There are two basic causes of cramping. One is inadequate oxygenation of muscle, and the other is lack of water or salt. Cramps from poor oxygenation can be improved by rapid deep breathing, and stretching the muscle. Cramps from lack of salt and water can be treated by stretching the muscle, drinking water and eating salty food (or drinking salty water). Pounding on the muscle can increase soreness.
What happens in a cramp is that lactic acid builds up because of normal anaerobic muscle metabolism. When the muscle burns sugar without enough oxygen, it makes lactic acid. The lactic acid finally becomes concentrated enough to trigger the contraction of the muscle. When the muscle lacks salt, the nerves firing the muscle are unable to recharge properly, causing a similar effect.
Nocturnal leg cramps are sudden, involuntary contractions of the calves that occur during the night or while at rest. Occasionally, muscles in the soles of the feet also become cramped. The sensation can last a few seconds or up to 10 minutes, but the soreness may linger. The cramps can affect persons in any age-group, but they tend to occur in middle-aged and older populations.
Nocturnal leg cramps should not be confused with restless legs syndrome, a crawling sensation that is relieved by walking or moving around. Although uncomfortable, restless legs syndrome typically does not involve cramping or pain.
References
- What are Cramps? (http://www.disabled-world.com/artman/publish/what-are-cramps.shtml)