ppr..perporagram raction
TRANSCRIPT
Pre-Programmed Reactions
Dr: Sh.T. Boroujeni
Masoud Zahiri
In the name of Allah
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Pre-Programmed Reactions
Definition and origins of preprogrammed reactionsElements of historySensory source ofpreprogrammed reactionsComplex nature ofpreprogrammed reactionsExamples of commonly studied preprogrammed reactions
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An unexpected perturbation of a joint gives rise to a sequence of EMG events in a stretched muscle. The first one (M1) comes at a short latency (under 40 ms). Then two peaks (M2 and M3) come at a latency of between 50 and 100 ms. M2 and M3 are addressed as pre-programmed reactions. Later, a voluntary correction comes.
EMG
Time
Perturbation
M1
M2 M3
Voluntaryreaction
Definition Pre-Programmed Reactions
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Elements of history
PPR were first discovered in humans and only later in animals
The first study Hammod(1954)In particular, they have been studied in humans
during such tasks as maintaining a joint (limb) posture, performing a quick joint movement, walking, standing, gripping an object, and speaking.
Pre-Programmed Reactions
Also called triggered reactions, M2–M3, functional stretch reflex, transcortical reflex, long-loop reflex
Come at an intermediate latency (40–100 ms) Are involuntary in nature but can be modified by
instruction Can be triggered by stimuli of virtually any modality Generate a quick, crude compensation for the
perturbation Are followed by voluntary corrections
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R. A.Schmidt
Definition Pre-Programmed Reactions
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Pre-programmed reactions demonstrate a strong dependence on the instruction.If the subject is instructed to resist perturbations, the pre-programmed reactions are large (solid lines). If the subject is asked to let the limb move,the pre-programmed reactions are much smaller (dashed lines). Note that the M1 reaction is the same.
Effect of Instruction on MuscleReactions to a Perturbation
EMG
Time
Perturbation
M1
M2 M3
Voluntaryreaction
ReactLet go
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A subject is holding a position in a joint against a load with a central command to a muscle. If the subject knows that a perturbation can occur, he/she can prepare an addition to the central command that would compensate for the predicted perturbation. The pre-programmed command (∆C) is triggered by peripheral signals generated by the perturbation and attenuates the mechanical effects of the perturbation.
A Possible Scheme
Muscle
Central command
Tonic stretch reflex mechanism
∆C
Afferents
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The actual source of the triggering signal for a pre-programmed reaction is not important as long as the signal carries sufficient information. It can be provided by proprioceptors, a flash of light, a loud tone, etc.
Pre-Programmed Responses Can Be Triggered by Any Sensory Signal
Muscle
Central command
Tonic stretch reflex mechanism
∆C
Proprioceptors
Vision
Hearing
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If a perturbation occurs during a fast voluntary movement, EMG changes are seen at a characteristic for the pre-programmed reactions latency. Generally, they involve an increase in the activity of a muscle that acts against the perturbation, and a decrease in the activity of a muscle that is assisted by the perturbation (bold lines).
Effects of a Perturbation AppliedDuring a Fast Movement
agonist
antagonisttime
EMGan increasein load
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Muscle vibration has different effects on different components of the responses to an external perturbation. The early response (M1) is suppressed just like the H-reflex, whereas the pre-programmed response (M2-M3) is unchanged.
Effects of Vibration on M1-2-3
Responses
Vibration
EMG
TimePerturbation
M1 M2-M3
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Examples of commonly studied preprogrammed reactions
1) Classical (lab conditions)
2) Grip Reactions
3) postural perturbations (ankle and hip strategies)
4) Preprogrammed Reactions in Locomotion
“Corrective stumbling reaction”
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One ofthe most commonly used methods to study preprogrammed reactions is to ask a subject to hold a position in a joint against a bias extemalload and then to change the load quickly.
Classical (lab conditions)
Pre-programmed postural corrections to a perturbation created by platform movement are context-dependent. If the cup is loaded with play dough, the corrections will be different than if the cup is full of hot tea.
Effects of Intentionon Quick Muscle Reactions
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Grip reaction
mechanical or electrical stimulation of the paw during locomotion induces different reactions in the swing and the stance phases. In the swing phase (A), there is a flexor reaction, so that the leg steps over a fictitious obstacle. In the stance phase (B), there is an extensor reaction, leading to the shortening of the stance phase for this limbA.
Corrective Stumbling Reaction
Surface
StimStim
A B
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Corrective stumbling reaction:
Preprogrammed Reactionsin Locomotion
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Occurs during locomotion
Can be induced by a mechanical stimulus to the foot
Represents a complex pattern of EMG changes
Leads to a quick step over the obstacle
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postural perturbations (ankle and hip strategies)
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Debra J. Rose,References
Richard A. Schmidt, WRISBERG LATSH
Thank you for your attention
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Stop judging others in order to meet composureDeepak Chopra