Download SPINAL CORD I

SPINAL CORD II
Reflexes of the
Spinal Cord
C.R. Houser
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Reflexes to be discussed • Stretch Reflex (Deep Tendon
Reflex or Myotatic Reflex)
• Golgi Tendon Organ Reflex
• Flexor Withdrawal Reflex and
Crossed Extension Reflex
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Muscle Spindle
Key to “Deep Tendon”
(Stretch) Reflexes
Emphasis on:
• Nuclear bag fiber
• Primary (Ia) afferent
(sensory) innervation
• Gamma motor
innervation
Nolte 9-13
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Stretch
Reflex and
Gamma Loop
Influences from:
1. Descending motor systems; and
2. Cutaneous afferents to Gamma
and Alpha motor neurons
Dorsal
Root
Gang.
Muscle
Spindle
Dorsal Nuc. Of
Clarke (C8-L2)
D. SpinoCerebell.
Tract
γ motor
α motor
Synergist
Extensor
Muscle
To Antagonist
Flexor
Muscle
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Muscle Spindle Responses
Purves, 16.11
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Alpha and Gamma
motor neuron
coactivation is
common.
Thus the muscle
spindles remain
sensitive even during
muscle contraction.
Purves, 16.11
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Roles of the Muscle Spindle
• Participates in automatic adjustments
of the body (i.e. to maintain posture).
• Compensates for changes in load
during motor activity.
• Contributes to normal muscle tone.
• Involved in sense of
limb position and
movement.
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Muscle spindle helps compensate for
changes in load.
Purves, Fig. 16.10
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Summary of Muscle Spindle
Function and the Stretch Reflex
• Muscle spindles are located in parallel with
regular muscle fibers.
• Primary afferents respond to stretch of the
muscle and contraction of the ends of the
spindle.
• Stimulation (stretch) of primary afferents of the
spindle leads to facilitation of motor neurons to
the same muscle.
• Gamma motor neurons receive input from
cutaneous afferents and descending motor
systems.
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Golgi Tendon Organ Reflex
Nolte 9-15
Purves 16.13
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Golgi Tendon Organ Responses
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Purves, 16.12
Roles of the Golgi Tendon Organ
• Provides negative feedback to regulate
muscle tension.
• Helps maintain steady level of force.
• Contributes to fine adjustments in the
force of contraction.
• Prevents muscles from generating
excessive tension.
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Comparison of Muscle Spindle and
Golgi Tendon Organ Activity
Purves, 16.12
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Comparison of Muscle Spindle and
Golgi Tendon Organ Activity
Purves, 16.12
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Flexor Withdrawal
Reflex
Crossed
Extension Reflex
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Central Pattern Generators
Purves 16.15
Local circuits in the spinal cord can control
complex, rhythmic patterns of movement,
such as those in locomotion.
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We’ll continue next week with:
• Brainstem – General Organization
• Major Motor and Sensory pathways
of the Spinal Cord
• Apply information – Spinal Cord
Injuries
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