Clonus is a set of involuntary and rhythmic muscular contractions and relaxations. Clonus is a sign of certain neurological conditions, particularly associated with upper motor neuronlesions involving descending motor pathways, and in many cases is accompanied by spasticity (another form of hyperexcitability).[1] 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 three to eight Hz on average, and may last a few seconds to several minutes depending on the patient’s condition.[1]
Clonus is most commonly found at the ankle, specifically with a dorsiflexion/plantarflexion movement (up and down).[2] Some case studies have also reported clonus in the finger, toe, and laterally in the ankle (as opposed to the typical up and down motion).[3][4]
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.[1] In order for self re-excitation to exist, both an increase in motor neuron excitability and nerve signal delay are required.[1] Increased motor neuron excitability is likely accomplished by alterations to the net inhibition of neurons occurring as a result of injury to the central nervous system (CNS) (stroke/ spinal cord injury).[1] This lack of inhibition biases neurons to a net excitatory state, therefore increasing total signal conduction.[1] Signaling delay is present due to an increased nerve conduction time.[1] Long delays are primarily due to long reflex pathways, which are common in distaljoints and muscles.[1] 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.[1]
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.[1]
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.[1] It is thought that the stretch reflex pathway may be stimulated first, and through its events, cause a decreased synaptic current threshold.[1] This decreased synaptic current threshold would enhance motor neuron excitability as nerve impulses would be more readily conducted, and thus turn on this central oscillator.[1] This theory is still being investigated.[1]
Clonus and spasticity
Clonus tends to co-exist with spasticity in many cases of stroke and spinal cord injury likely due to their common physiological origins.[1] Some consider clonus as simply an extended outcome of spasticity.[1] Although closely linked, clonus is not seen in all patients with spasticity.[1] Clonus tends to not be present with spasticity in patients with significantly increased muscle tone, as the muscles are constantly active and therefore not engaging in the characteristic on/off cycle of clonus.[1]
Clonus results due to an increased motor neuron excitation (decreased action potentialthreshold) and is common in muscles with long conduction delays, such as the long reflex tracts found in distalmuscle groups.[1] Clonus is commonly seen in the ankle but may exist in other distal structures as well.[2]
Diagnosis
Clonus at the ankle is tested by rapidly flexing the foot into dorsiflexion (upward), inducing a stretch to the gastrocnemius muscle.[1] Subsequent beating of the foot will result, however only a sustained clonus (5 beats or more) is considered abnormal[citation needed]. Clonus can also be tested in the knees by rapidly pushing the patella (knee cap), towards the toes.
^ abcdefghijklmnopqrstHilder, Joseph M.; Zev W. Rymer (September 1999). "A Stimulation Study of Reflex Instability in Spasticity: Origins of Clonus". IEEE Transactions on Rehabilitation Engineering. 7 (3): 327–340. doi:10.1109/86.788469. PMID 10498378.
^ abcdeDouglas, Wallace M.; Bruce H Ross; Christine K. Thomas (Aug 25, 2005). "Motor unit behaviour during clonus". Journal of Applied Physiology. 99 (6): 2166–2172. CiteSeerX10.1.1.501.9581. doi:10.1152/japplphysiol.00649.2005. PMID 16099891.
^ abcWeisenburg, Theodore H (November 1903). "Triceps, Biceps and Finger Clonus". Journal of Nervous and Mental Disease. 30 (11): 681–683. doi:10.1097/00005053-190311000-00003. S2CID 143749312.
^Mitchell, John K. (May 1902). "Two unusual forms of clonus: toe clonus and lateral ankle clonus". Journal of Nervous and Mental Disease. 29 (5): 260–261. doi:10.1097/00005053-190205000-00002. S2CID 145648718.
^Anthony, J; Damasceno, A; Ojjii, D (2016-05-18). "Hypertensive disorders of pregnancy: what the physician needs to know". Cardiovascular Journal of Africa. 27 (2): 104–110. doi:10.5830/CVJA-2016-051. PMC4928160. PMID 27213858.
External links
Look up clonus in Wiktionary, the free dictionary.
Dr. Gilman on Serotonin Toxicity
Video about Clonus at the ankle
Video about Clonus at the knee (patella)
December 28, 2022
clonus, film, parts, horror, involuntary, rhythmic, muscular, contractions, relaxations, sign, certain, neurological, conditions, particularly, associated, with, upper, motor, neuron, lesions, involving, descending, motor, pathways, many, cases, accompanied, s. For the film see Parts The Clonus Horror Clonus is a set of involuntary and 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 1 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 three to eight Hz on average and may last a few seconds to several minutes depending on the patient s condition 1 ClonusSpecialtyNeurology source source source source source source source source source source source source Ankle clonus Contents 1 Signs 2 Cause 3 Mechanism 3 1 Hyperactive stretch reflexes 3 2 Central oscillator 3 3 Clonus and spasticity 4 Diagnosis 5 See also 6 References 7 External linksSigns EditClonus is most commonly found at the ankle specifically with a dorsiflexion plantarflexion movement up and down 2 Some case studies have also reported clonus in the finger toe and laterally in the ankle as opposed to the typical up and down motion 3 4 Ankle medial gastrocnemius 2 Patella knee cap Triceps surae 2 3 Biceps brachii 3 Cause EditClonus is typically seen in people with cerebral palsy stroke multiple sclerosis spinal cord damage and hepatic encephalopathy 2 It can occur in epilepsy as part of a generalized tonic clonic seizure and in pregnant women presenting with severe pre eclampsia and eclampsia 5 It can also be an adverse drug reaction such as after ingestion of potent serotonergic drugs where clonus strongly predicts imminent serotonin toxicity serotonin syndrome Mechanism EditHyperactive stretch reflexes Edit 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 1 In order for self re excitation to exist both an increase in motor neuron excitability and nerve signal delay are required 1 Increased motor neuron excitability is likely accomplished by alterations to the net inhibition of neurons occurring as a result of injury to the central nervous system CNS stroke spinal cord injury 1 This lack of inhibition biases neurons to a net excitatory state therefore increasing total signal conduction 1 Signaling delay is present due to an increased nerve conduction time 1 Long delays are primarily due to long reflex pathways which are common in distal joints and muscles 1 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 1 Central oscillator Edit 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 1 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 1 It is thought that the stretch reflex pathway may be stimulated first and through its events cause a decreased synaptic current threshold 1 This decreased synaptic current threshold would enhance motor neuron excitability as nerve impulses would be more readily conducted and thus turn on this central oscillator 1 This theory is still being investigated 1 Clonus and spasticity Edit Clonus tends to co exist with spasticity in many cases of stroke and spinal cord injury likely due to their common physiological origins 1 Some consider clonus as simply an extended outcome of spasticity 1 Although closely linked clonus is not seen in all patients with spasticity 1 Clonus tends to not be present with spasticity in patients with significantly increased muscle tone as the muscles are constantly active and therefore not engaging in the characteristic on off cycle of clonus 1 Clonus results due to an increased motor neuron excitation decreased action potential threshold and is common in muscles with long conduction delays such as the long reflex tracts found in distal muscle groups 1 Clonus is commonly seen in the ankle but may exist in other distal structures as well 2 Diagnosis EditClonus at the ankle is tested by rapidly flexing the foot into dorsiflexion upward inducing a stretch to the gastrocnemius muscle 1 Subsequent beating of the foot will result however only a sustained clonus 5 beats or more is considered abnormal citation needed Clonus can also be tested in the knees by rapidly pushing the patella knee cap towards the toes See also EditMyoclonus Generalized tonic clonic seizure Stretch reflex Tetany Tetanic contractionsReferences Edit a b c d e f g h i j k l m n o p q r s t Hilder Joseph M Zev W Rymer September 1999 A Stimulation Study of Reflex Instability in Spasticity Origins of Clonus IEEE Transactions on Rehabilitation Engineering 7 3 327 340 doi 10 1109 86 788469 PMID 10498378 a b c d e Douglas Wallace M Bruce H Ross Christine K Thomas Aug 25 2005 Motor unit behaviour during clonus Journal of Applied Physiology 99 6 2166 2172 CiteSeerX 10 1 1 501 9581 doi 10 1152 japplphysiol 00649 2005 PMID 16099891 a b c Weisenburg Theodore H November 1903 Triceps Biceps and Finger Clonus Journal of Nervous and Mental Disease 30 11 681 683 doi 10 1097 00005053 190311000 00003 S2CID 143749312 Mitchell John K May 1902 Two unusual forms of clonus toe clonus and lateral ankle clonus Journal of Nervous and Mental Disease 29 5 260 261 doi 10 1097 00005053 190205000 00002 S2CID 145648718 Anthony J Damasceno A Ojjii D 2016 05 18 Hypertensive disorders of pregnancy what the physician needs to know Cardiovascular Journal of Africa 27 2 104 110 doi 10 5830 CVJA 2016 051 PMC 4928160 PMID 27213858 External links Edit Look up clonus in Wiktionary the free dictionary Dr Gilman on Serotonin Toxicity Video about Clonus at the ankle Video about Clonus at the knee patella Retrieved from https en wikipedia org w index php title Clonus amp oldid 1127497609, wikipedia, wiki, book, books, library,
