Myoclonus true UMLS:C0027066 UMLS:C1854302 myoclonic contraction Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements. HP:0007087 myoclonic jerk Jerking SNOMEDCT_US:127324008 MSH:D009207 HP:0001336 human_phenotype SNOMEDCT_US:17450006 Myoclonus may be synchronous (several muscle contracting simultaneously), spreading (several muscles contracting in sequence), or asynchronous (several muscles contracting with varying and unpredictable relative timing). Myoclonus is characterized by sudden unidirectional movement due to muscle contraction (positive myoclonus) or due to sudden brief muscle relaxation (negative myoclonus). Myoclonic jerks Involuntary jerking movements HP:0002535 Involuntary movements