Myoclonus
Myoclonus is a brief, involuntary, irregular twitching of a muscle, a joint, or a group of muscles, different from clonus, which is rhythmic or regular. Myoclonus describes a medical sign and, generally, is not a of a disease. It belongs to the hyperkinetic movement disorders, among tremor and chorea for example. These myoclonic twitches, jerks, or are usually caused by sudden muscle contractions or brief lapses of contraction. The most common circumstance under which they occur is while falling asleep. Myoclonic jerks occur in healthy people and are experienced occasionally by everyone. However, when they appear with more persistence and become more widespread they can be a sign of various disorders. Hiccups are a kind of myoclonic jerk specifically affecting the diaphragm. When a spasm is triggered by an external stimulus, it is known as a provoked spasm. Shuddering attacks in babies fall in this category.
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