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Refexes
Chapter 19
KINE 3301Biomechanics o Human
Movement
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Monosnaptic ! "o#snapic Connections
$he Ia a%erent neuron rom the musc#e spine is
the on# sensor '(er to ma)e a monosnaptic
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• $he e%erent neura#response can (e
mo&i'e& (monosnaptic orinterneuron input*
"resnaptic Inhi(ition! +aci#itation
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Musc#e ,pine ,tructure
Intrausua# +i(ers- the term intrausa# '(ers reers to the musc#e
spineto &i%erentiate it rom the extrausa# .norma#
musc#e/*+usimotor ,stem- the usimotor sstem reers to the musc#e
spine
its a%erent e%erent an& specia#i2e& musc#e tissue*
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Nerve
Con&uctionve#ocit-
Ia 0 4 90m5sII 30 4 67m5s
,pina#Connections
$he Ia
neuronma)esmonosnapticconnections
8ith a#phaan& amma*
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:hen a musc#e
spine is stretche&a(ove its currentsensitivit it e#icits
astretch refex-1* Ia stimu#ates
a#pha 4 aonist !snerist*
;* Ia inhi(itsantaonist*
3* Ia stimu#atesamma
,tretch Refex
$he num(er oimpu#ses propaate&up the Ia neuron
isre#ate& to themanitu&e an& rate
o stretch*
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Inverse ,tretchRefex
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$he I( neuron
8eaves in an&out o theten&onsco##aen'(ers* $he
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Refex #atenciesrom cutaneousreceptors varrom 70 4 @7 ms*
Cutaneous Receptors
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Converence osina#s to the
motor neuron canmo&u#ate the inputto the motorneuron an&
itsoutput response toa stimu#us*
Converence ! Mo&u#ationo ,ensor ,ina#s
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• Refexes 8ere once thouht to (e
invariant* It 8as assume& that the 8erecomp#ete#
invo#untar*• :e no8 vie8 the terms refex an&
vo#untar as (ein on a continuum 8ith
pure refexes such as an ee (#in) or astretch refex on one
en& an& comp#etean& u## conscious contro# on the other
en&*
• $he spee& 8ith 8hich a movement or orce
is enerate& &etermines the extent to8hich ee&(ac) is
a(#e to correct errors*
• In ee&(ac) contro# the movement is s#o8enouh .A 70 ms/
that refex sina#s can
mo&i movement*
+ee&(ac) an& +ee&or8ar& Contro#
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• $he minimum time or the neuromuscu#ar
sstem to respon& to a stimu#us is @0 4;00 ms*• Refex time 30
4 1;0 ms• Musc#e orce time 70 4 300 ms
Consi&er the o##o8in scenarios 8hich areee&(ac) an&
ee&or8ar&-• urin the up8ar& phase o a vertica# Dump
can ou chane rom Dumpin up to
Dumpin up ! or8ar&• :hen #an&in on a ru i the ru
is
unexpecte pu##e& (ac)8ar& at theinstant our eet touch
the ru 8hat
happens
+ee&(ac) ! +ee&or8ar&
