Editing Spasticity (section)

== Characteristics of spasticity ==
[[File:03 Resistance vs stretch.svg|thumb|Characteristics of spasticity]]
A commonly known feature of spasticity, known as [[Clasp-knife response]] is the sudden decrease of tone after initial resistance, also referred to as a lengthening reaction or a "catch-yield sequence".<ref>{{Cite journal |last1=Mukherjee |first1=Angshuman |last2=Chakravarty |first2=Ambar |date=2010 |title=Spasticity Mechanisms – for the Clinician |journal=Frontiers in Neurology |volume=1 |page=149 |doi=10.3389/fneur.2010.00149 |pmid=21206767 |issn=1664-2295|pmc=3009478 |doi-access=free }}</ref> This is because of inverse stretch reflex activation mediated by the Golgi tendon organ on sustained muscle stretching resulting in sudden relaxation of the muscle.<ref name=":0">{{Cite journal |last1=Ramanathan |first1=Venkateswaran |last2=Baskar |first2=Dipti |last3=Pari |first3=Hariswar |date=2022 |title='Seatbelt Effect' of spasticity: Contrasting velocity dependence from the clasp knife phenomenon |url=http://www.annalsofian.org/text.asp?2022/25/3/517/338853 |journal=Annals of Indian Academy of Neurology |language=en |volume=25 |issue=3 |pages=517–519 |doi=10.4103/aian.aian_817_21 |pmid=35936584 |issn=0972-2327|pmc=9350785 |doi-access=free }}</ref> 

Another characteristic of spasticity, which may be referred to as "seatbelt effect" of spasticity, is different as the amount of resistance offered by the muscle is directly proportional to velocity of the passive movement.<ref>{{Cite journal |last=Petek Balci |first=Belgin |date=2018 |title=Spasticty measurement |url=http://submission.noropsikiyatriarsivi.com/default.aspx?s=public~kabul&mId=23339 |journal=Archives of Neuropsychiatry |volume=55 |issue=Suppl 1 |pages=S49–S53 |language=en |doi=10.29399/npa.23339 |pmid=30692856 |issn=1309-4866|pmc=6278623 }}</ref> It is caused by increased muscle spindle excitability and velocity sensitivity of Ia spindle afferent nerve fibres, resulting in excessive activation of alpha motor neurons of the spinal cord.<ref>{{Citation |last=Ko |first=Hyun-Yoon |title=Functional Neuroanatomy of the Spinal Cord |date=2022 |url=http://dx.doi.org/10.1007/978-981-19-0228-4_3 |work=Management and Rehabilitation of Spinal Cord Injuries |pages=41–68 |access-date=2023-07-31 |place=Singapore |publisher=Springer Nature Singapore |doi=10.1007/978-981-19-0228-4_3 |isbn=978-981-19-0227-7}}</ref> It is similar to the tug we feel initially while pulling the seatbelt of a car beyond a certain velocity, hence the name "seatbelt effect"<ref name=":0" />