Download REFLEX PHYSIOLOGY

NEUROMUSCULOSKELETAL SYSTEMS
LECTURE 10
REFLEX PHYSIOLOGY
Medical Science
Dr R G Luckwill
KNEE JERK REFLEX (Monosynaptic Reflex)
Extensor muscle of knee
(quadriceps femoris)
Muscle
spindle
Patellar tendon
Alpha motor
neuron
Figure 8.26
Page 285
Capsule
Alpha motor
neuron axon
Gamma motor
neuron axon
Secondary (flower-spray)
endings of afferent
fibers
Extrafusal (“ordinary”)
muscle fibers
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
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MUSCLE INNERVATION
Extrafusal
Ia
II
Annulospiral
(primary)
Flower Spray
(secondary)
α -motor
Intrafusal
γ-motor
Firing Rate
Spindle Ending Responses
Secondary
Stretch
Primary
Time
KNEE JERK REFLEX (Monosynaptic Reflex)
Extensor muscle of knee
(quadriceps femoris)
Muscle
spindle (Primary endings)
Ia Sensory neuron
Single synapse
Patellar tendon
Alpha motor
neuron
Figure 8.26
Page 285
WITHDRAWL (FLEXION) REFLEX
&
ANTAGONIST INHIBITION REFLEX
Thermal
pain receptor
in finger
Afferent
Pathway
= Inhibitory interneuron
= Excitatory interneuron
= Synapse
= Inhibits
= Stimulates
Ascending pathway
to brain
Stimulus
Biceps
(flexor)
contracts
Hand
withdrawn
Efferent pathway
Triceps
(extensor)
relaxes
Integrating center
(spinal cord)
Effector
organs
Response
Figure 5.31
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WITHDRAWL & CROSSED EXTENSOR REFLEXES
Afferent
pathway
Efferent
pathway
Efferent
pathway
Flexor
muscle
contracts
Pain
receptor
in heel
Extensor
muscle
relaxes
Injured
extremity
(effector
organ)
Response
Integrating center
(spinal cord)
Flexor
muscle
relaxes
Extensor
muscle
contracts
Opposite
extremity
(effector
organ)
Stimulus
Response
Figure 5.32
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Levels of Reflex Connections
Figure 8.26 (1)
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Extrafusal
skeletal
muscle fiber
Spinal
cord
Intrafusal
muscle
spindle fiber
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)
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α−γ COACTIVATION
Relaxed muscle; spindle
fiber sensitive to stretch
of muscle
Contracted muscle in
hypothetical situation of
no spindle coactivation;
slackened spindle fiber
not sensitive to stretch
of muscle
Contracted muscle in
normal situation of
spindle coactivation;
contracted spindle fiber
sensitive to stretch of
muscle
Figure 8.25 (2)
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MUSCLE INNERVATION
Extrafusal
Ia
II
Annulospiral
(primary)
Flower Spray
(secondary)
α -motor
Intrafusal
γ-motor
Servo-mechanism of Muscle Contraction
1. Descending command to γ-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 α-motoneurons
6. Contraction of Extrafusal muscle fibres
Synaptic inputs
(presynaptic axon terminals)
Dendrites
Cell body of
Motor Neuron
Axon
hillock
Axon
Myelin
sheath
Figure 4.15
Page 102
Motor Neuron Connections
Swing
Stance
100%
Normal
(Resting)
Walking
0%
Time
Excitability of Gastrocnemius H-Reflex
during Walking