<unk>  is a brief, involuntary, irregular (lacking rhythm) twitching of a muscle or a group of muscles, different from clonus, which is rhythmic or regular.<unk>  describes a medical sign and, generally, is not a diagnosis of a disease. These myoclonic twitches, jerks, or seizures are usually caused by sudden muscle contractions (positive<unk>  or brief lapses of contraction (negative<unk> . The most common circumstance under which they occur is while falling asleep (hypnic jerk). 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 neurological disorders. Hiccups are a kind of myoclonic jerk specifically affecting the diaphragm. When a spasm is caused by another person it is known as a provoked spasm. Shuddering attacks in babies fall in this category. Myoclonic jerks may occur alone or in sequence, in a pattern or without pattern. They may occur infrequently or many times each minute. Most often,<unk>  is one of several signs in a wide variety of nervous system disorders such as multiple sclerosis, Parkinson's disease, dystonia, Alzheimer's disease, Gaucher's disease, subacute sclerosing panencephalitis, Creutzfeldt–Jakob disease (CJD), serotonin toxicity, some cases of Huntington's disease, some forms of epilepsy, and occasionally in intracranial hypotension. In almost all instances in which<unk>  is caused by central nervous system disease it is preceded by other symptoms; for instance, in CJD it is generally a late-stage clinical feature that appears after the patient has already started to exhibit gross neurological deficits. Anatomically,<unk>  may originate from lesions of the cortex, subcortex or spinal cord. The presence of<unk>  above the foramen magnum effectively excludes spinal<unk> ; further localisation relies on further investigation with electromyography (EMG) and electroencephalography (EEG).
Myoclonus
Chorea 
Chorea
Clonus
Opisthotonus
Opsoclonus
Synkinesis
Paratonia