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Myoclonus refers to very rapid and brief muscular activity. These movements are involuntary- the medical term meaning not under one’s control.
There are a number of types of involuntary muscle activities for example seizures, dystonias, fasciculations, myoclonus, chorea and others.Unlike fasciculations which indicate the absence of nervous system input, myoclonus originates in the nervous system. The source of myoclonus can be at any one of many different levels of the central nervous sytem (=brain , spinal cord and alll of their parts).

There are a number of different types of myoclonus. Everyone has had sleep myoclonus- most often a leg suddenly extends (unbends) rapidly while asleep. Outside of the sleep state, however, myoclonus is usually abnormal. There are a few forms which do not indicate serious neurologic problems: benign myoclonus of infancy, and benign febrile myoclonus (only occurs during a fever episode).

Myoclonus in other forms may indicate risk of neurologic deterioration, and may be associated with seizures.