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NEUROMUSCULOSKELETAL SYSTEMS
LECTURE 10
REFLEX PHYSIOLOGY
Medical Science Dr R G Luckwill
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Alpha motor
neuron axon
Gamma motor
neuron axon
Secondary (flower-spray)
endings of afferent
fibers
Extrafusal (ordinary)
muscle fibers
Capsule
Intrafusal (spindle)muscle fibers
Contractile end portions
of intrafusal fiber
Noncontractile
central portion
of intrafusal
fiber
Primary (annulospiral)
endings of afferent fibers
Figure 8.24
Page 283
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MUSCLE INNERVATION
Ia
II
!-motor
"-motor
Extrafusal
Annulospiral (primary)
Flower Spray
(secondary)
Intrafusal
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Time
tretch
rnRae
rimary
econdary
Spindle Ending Responses
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Figure 8.26
Page 285
Extensor muscle of knee
(quadriceps femoris)
Muscle
spindle
Alpha motor
neuron
Patellar tendon
KNEE JERK REFLEX (Monosynaptic Reflex)
(Primary endings)
Ia Sensory neuron
Single synapse
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Figure 5.31
Page 174
Stimulus
Biceps
(flexor)
contracts
Handwithdrawn
Triceps
(extensor)
relaxes
Ascending pathway
to brain
Response
Integrating center
(spinal cord)
Thermalpain receptor
in finger
Efferent pathway
Effector
organs
= Inhibitory interneuron
= Excitatory interneuron
= Synapse
= Inhibits
= Stimulates
Afferent
Pathway
WITHDRAWL (FLEXION) REFLEX
&
ANTAGONIST INHIBITION REFLEX
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Figure 5.32
Page 175
Efferent
pathway
Afferent
pathway Efferent
pathway
Flexor
muscle
contracts
Extensor
muscle
relaxes
Flexormuscle
relaxes
Extensormuscle
contracts
Stimulus
Response
Pain
receptor
in heel
Injured
extremity
(effector
organ)
Integrating center
(spinal cord)
Opposite
extremity
(effector
organ)
Response
WITHDRAWL & CROSSED EXTENSOR REFLEXES
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Levels of Reflex Connections
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Figure 8.26 (1)
Page 287
Extrafusal
skeletal
muscle fiber
Intrafusal
muscle
spindle fiber
Spinal
cord
Afferent input from sensory endings of muscle spindle fiber
Alpha motor neuron output to regular skeletal-muscle fiber
Stretch reflex pathway
Gamma motor-neuron output to contractile end portions of spindle fiber
Descending pathways coactivating alpha and gamma motor neurons
Figure 8.25 (1)
Page 284
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Relaxed muscle; spindle
fiber sensitive to stretch
of muscle
Contracted muscle in
hypothetical situation of
no spindle coactivation;
slackened spindle fibernot sensitive to stretch
of muscle
Contracted muscle in
normal situation of
spindle coactivation;
contracted spindle fibersensitive to stretch of
muscle
Figure 8.25 (2)
Page 284
# COACTIVATION
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MUSCLE INNERVATION
Ia
II
!-motor
"-motor
Extrafusal
Annulospiral (primary)
Flower Spray
(secondary)
Intrafusal
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Servo-mechanism of Muscle Contraction
1. Descending command to -motoneuron
2. Ends of Intrafusal fibres contract
3. Spindle endings stretched & fire
4. AP volleys in Ia & II sensory fibres to Spinal cord
5. Reflex AP volley in -motoneurons
6. Contraction of Extrafusal muscle fibres
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Figure 4.15
Page 102
Synaptic inputs
(presynaptic axon terminals)
Dendrites
Cell body of
Motor Neuron
Axon
hillock
Axon
Myelin
sheath
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Motor Neuron Connections
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Swing Stance
Normal(Resting)
Walking
Time
100%
0%
Excitability of Gastrocnemius H-Reflexduring Walking