An involuntary, and, in severe cases, painful contraction of a muscle or of a hollow organ with a muscular wall. Spasm may be due to some disturbance of function in the muscle where it occurs or it may originate in some abnormality of that part of the nervous system which controls the muscles. Spasms of a general nature are usually spoken of as CONVULSIONS; spasms of a painful nature are known as cramp (see under MUSCLES, DISORDERS OF) when they affect the muscles of the limbs, and as COLIC when they are situated in the stomach, intestines, ureters or bile duct, or other organs of the abdomen. Spasm of the heart is called ANGINA PECTORIS, and is both a serious and an agonising condition. When the spasm is a prolonged firm contraction, it is spoken of as tonic spasm; when it consists of a series of twitches or quick alternate contractions and relaxations, it is known as clonic spasm. Spasm is a symptom of many diseases.