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Chapter 13
Integrative Physiology I:
Control of Body Movement
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About this Chapter
• Neural reflexes• Autonomic reflexes• Skeletal muscle reflexes• The integrated control of body movement• Control of movement in visceral muscles
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Neural Reflexes
Table 13-1
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Somatic Motor Reflexes
• Monosynaptic and polysynaptic somatic motor reflexes
Figure 13-1a
StimulusSensoryneuron
Receptor
Efferentneuron
Target celleffectorResponse
(a) A monosynaptic reflex has a single synapse between the afferent and efferent neurons.
Spinalcord
Integrating center
Onesynapse
Somaticmotor neuron
Skeletal muscle
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Somatic Motor Reflexes
Figure 13-1b
Response
StimulusSensoryneuron
Efferentneuron
Interneuron
(b) Polysynaptic reflexes have two or more synapses.
Target celleffector
Spinalcord
Integrating center
Receptor
Synapse 1
Synapse 2
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Postganglionicautonomic
neuron
Preganglionicautonomic
neuron
CNSintegrating
center
SensoryneuronReceptorStimulus
Response
Targetcell
Autonomicganglion
Autonomic ReflexesSome visceral reflexes are spinal reflexes
no brain involvement, or brain modulated
“bashful bladder” / toilet training / goose pimples
Figure 13-2
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Skeletal Muscle Reflexes
• Proprioceptors are located in skeletal muscle, joint capsules, and ligaments
• Proprioceptors carry input sensory neurons to CNS
• CNS integrates input signal• Somatic motor neurons carry output signal• Alpha motor neurons α
• Effectors are contractile skeletal muscle fibers extrafusal muscle fibers
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Proprioceptors
• Muscle spindle• Response to stretch• Within muscle fibers as intrafusal fibrer• Automonic with gamma motor neurons
• Golgi tendon organ• Muscle tension especially during isometric• Relaxation reflex - protective
• Joint receptors• Are found in capsules and ligaments around
joints
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Proprioceptors
• Muscle spindles and Golgi tendon organs are sensory receptors in muscle
Figure 13-3a
Musclespindle
Extrafusal muscle fibers
Tendon
Alpha motorneuron
Golgi tendon organ
(a)
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Proprioceptors
Figure 13-3b
Musclespindle
Extrafusal fiber
Intrafusal fibers
Central regionlacks myofibrils.
Gamma motor neurons
Tonically active sensoryneurons
Gamma motor neuronsfrom CNS
(b) Muscle spindle
To CNSSpindle fibers: Sense stretch
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Proprioceptors
Figure 13-3c
(c) Golgi tendon organ
Extrafusalmuscle fibers
Sensory neuron
Collagenfiber
Capsule
Tendon
Afferent neuron
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Muscle Spindles
• Muscle spindles monitor muscle length and prevent overstretching
Figure 13-4a
Sensory neuronendings
Intrafusal fibersof muscle spindle
(a) Spindles are firing even when muscle is relaxed.
Spinal cord
Sensoryneuron
Alpha motorneuron
Extrafusal musclefibers at resting length
Sensory neuron is tonically active.
Spinal cord integrates function.
Alpha motor neurons toextrafusal fibers receive tonicinput from muscle spindles.
Extrafusal fibers maintain a certainlevel of tension even at rest.
1
2
3
4
5
1
2
3
4
5
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Muscle Spindles
Figure 13-4b
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Alpha-Gamma Coactivation
Figure 13-5a
1
1
1
2
2
3
(a) Alpha-gamma coactivation
Musclelength
Muscle shortens
Intrafusal fibers do not slacken sofiring rate remains constant.
Muscle shortens
Action potentialsof spindle
sensory neuron
Time
Alpha motor neuron firesand gamma motor neuronfires.
Muscle contracts.
Stretch on centers ofintrafusal fibers unchanged.Firing rate of afferentneuron remains constant.
1
2
3
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Without Gamma Motor Neurons
Figure 13-5b
1
2
3
4
1
2
3
4
(b)
Muscle shortens
Action potential
Muscle shortens
Time
Alpha motor neuron fires.
Less stretch on centerof intrafusal fibers
Firing rate of spindlesensory neuron decreases.
Muscle contracts.
Less stretch onintrafusal fibers
Musclelength
Action potentialsof spindle
sensory neuron
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Muscle Reflexes Help Prevent Damage
Figure 13-6a
Sensory neuron
Spindle Spinalcord
Motor neuron Add load
Muscle
(a) Load added to muscle.
Muscle spindle reflex
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Muscle Reflexes Help Prevent Damage
Figure 13-6b
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GTO’s
Figure 13-7
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Movement
• Types of movement• Reflex• Voluntary• Rhythmic
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CNS Integrates Movement
• Spinal cord integrates spinal reflexes and contains central pattern generators
• Brain stem and cerebellum control postural reflexes and hand and eye movements
• Cerebral cortex and basal ganglia • Voluntary movement
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CNS Integrates Movement
Table 13-3
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CNS Control of Voluntary Movement
Figure 13-10
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CNS Control of Voluntary Movement
• Feedforward reflexes and feedback of information during movement
Figure 13-13
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Parkinson’s Disease
• Progressive neural disorder• Characterized by abnormal movements,
speech difficulties, and cognitive changes• Loss of basal ganglia that release
dopamine
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Visceral Movement
• Moves products in hollow organs• Controlled by ANS• Some create own action potentials
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Summary
• Neural reflexes• Somatic reflexes, autonomic reflexes, spinal
reflexes, cranial reflexes, monosynaptic reflex, and polysynaptic reflex
• Autonomic reflexes • Skeletal muscle reflexes• Extrafusal muscle fibers, alpha motor neurons,
muscle spindles, intrafusal fibers, gamma motor neurons, muscle tone, and stretch reflex
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Summary
• Skeletal muscle reflexes (continued)• Alpha-gamma coactivation, golgi tendon
organs, myotatic unit, reciprocal inhibitions, flexion reflexes, crossed extensor reflex, and central pattern generator
• Integrated control• Reflex movement, postural reflexes, voluntary
movement, rhythmic movements, corticospinal tract, basal ganglia, and feedforward reflexes
• Control of movement in visceral muscles