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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