 clonus (from the greek for "violent, confused motion") is a series of involuntary, rhythmic, muscular contractions and relaxations. clonus is a sign of certain neurological conditions, particularly associated with upper motor neuron lesions involving descending motor pathways, and in many cases is, accompanied by spasticity (another form of hyperexcitability). unlike small, spontaneous twitches known as fasciculations (usually caused by lower motor neuron pathology), clonus causes large motions that are usually initiated by a reflex. studies have shown clonus beat frequency to range from 3â8 hz on average, and may last a few seconds to several minutes depending on the patientâs condition. ==susceptibility== clonus is typically seen in patients with stroke, multiple sclerosis,  spinal cord damage and hepatic encephalopathy. clonus has also appeared after ingesting potent serotonergic drugs, where ingestion strongly predicts imminent serotonin toxicity (serotonin syndrome). == mechanism of clonus == ===two proposed mechanisms=== 1) self re-excitation of hyperactive stretch reflexes: the self re-excitation of hyperactive stretch reflexes theory involves a repetitive contract- relax cycle in the affected muscle, which creates oscillatory movements in the affected limb. in order for self re-excitation to exist, both an increase in motor neuron excitability and nerve signal delay are required. increased motor neuron excitability is likely accomplished by alterations to the net inhibition of neurons occurring as a result of injury to the cns (stroke/ spinal cord injury). this lack of inhibition biases neurons to a net excitatory state, therefore increasing total signal conduction. signaling delay is present due to an increased nerve conduction time. long delays are primarily due to long reflex pathways, which are common in distal joints and muscles. this may therefore explain why clonus is typically found in distal structures like the ankle. frequency of clonus beats have been found to be directly proportional to the length of the reflex pathway it is found in. 2) presence of a central oscillator: clonus, with respect to the presence of a central oscillator, functions on the theory that when the central oscillator is turned on by a peripheral event, it will continue to rhythmically excite motor neurons; therefore creating clonus. although the two proposed mechanisms are very different in [theory] and are still debated, some studies now propose the potential of both mechanisms co-existing to create clonus. it is thought that the stretch reflex pathway may be stimulated first, and through its events, cause a decreased [[syna
Medical_signs Seizure_types