Chapter 13
Integrative
Physiology I:
Control of Body
Movement
About this Chapter
•
•
•
•
•
Neural reflexes
Autonomic reflexes
Skeletal muscle reflexes
The integrated control of body movement
Control of movement in visceral muscles
Neural Reflexes
Table 13-1
Somatic Motor Reflexes
• Monosynaptic and polysynaptic somatic
motor reflexes
(a) A monosynaptic reflex has a single synapse between the afferent and efferent neurons.
Stimulus
Sensory
neuron
Receptor
Spinal
cord
Integrating
center
Skeletal muscle
Somatic
motor neuron
Response
Target cell
effector
Efferent
neuron
One
synapse
Figure 13-1a
Somatic Motor Reflexes
(b) Polysynaptic reflexes have two or more synapses.
Synapse 1
Stimulus
Receptor
Spinal
cord
Integrating
center
Sensory
neuron
Interneuron
Response
Target cell
effector
Efferent
neuron
Synapse 2
Figure 13-1b
Autonomic Reflexes
Some visceral reflexes are spinal reflexes
no brain involvement, or brain modulated
“bashful bladder” / toilet training / goose pimples
Stimulus
Receptor
Sensory
neuron
CNS
integrating
center
Preganglionic
autonomic
neuron
Response
Postganglionic
autonomic
neuron
Target
cell
Autonomic
ganglion
Figure 13-2
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
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
Proprioceptors
• Muscle spindles and Golgi tendon organs are
sensory receptors in muscle
Extrafusal muscle fibers
Alpha motor
neuron
Golgi tendon organ
(a)
Muscle
spindle
Tendon
Figure 13-3a
Proprioceptors
Spindle
fibers: Sense
stretch
Gamma motor neurons
To CNS
Tonically active sensory
neurons
Central region
lacks myofibrils.
Gamma motor neurons
from CNS
Muscle
spindle
Intrafusal fibers
Extrafusal fiber
(b) Muscle spindle
Figure 13-3b
Proprioceptors
Extrafusal
muscle fibers
Afferent neuron
Capsule
Sensory neuron
Collagen
fiber
Tendon
(c) Golgi tendon organ
Figure 13-3c
Muscle Spindles
• Muscle spindles monitor muscle length and
prevent overstretching
1
Sensory neuron
endings
Intrafusal fibers
of muscle spindle
3
2
1 Extrafusal muscle
fibers at resting length
2 Sensory neuron is tonically active.
Sensory
neuron
3 Spinal cord integrates function.
Alpha motor
neuron
Spinal cord
4
4
Alpha motor neurons to
extrafusal fibers receive tonic
input from muscle spindles.
5
(a) Spindles are firing even when muscle is relaxed.
5 Extrafusal fibers maintain a certain
level of tension even at rest.
Figure 13-4a
Muscle Spindles
Figure 13-4b
Alpha-Gamma Coactivation
(a) Alpha-gamma coactivation
1
1
2
1
1 Alpha motor neuron fires
and gamma motor neuron
fires.
2
3
Muscle shortens
Muscle
length
2 Muscle contracts.
Intrafusal fibers do not slacken so
firing rate remains constant.
3 Stretch on centers of
intrafusal fibers unchanged.
Firing rate of afferent
neuron remains constant.
Action potentials
of spindle
sensory neuron
Muscle shortens
Time
Figure 13-5a
Without Gamma Motor Neurons
(b)
1
1 Alpha motor neuron fires.
3
2
2 Muscle contracts.
4
3 Less stretch on center
of intrafusal fibers
4 Firing rate of spindle
sensory neuron decreases.
Muscle shortens
Muscle
length
Less stretch on Action potential
intrafusal fibers
Action potentials
of spindle
sensory neuron
Muscle shortens
Time
Figure 13-5b
Muscle Reflexes Help Prevent Damage
Muscle spindle reflex
Sensory neuron
Spindle
Spinal
cord
Add load
Motor neuron
Muscle
(a) Load added to muscle.
Figure 13-6a
Muscle Reflexes Help Prevent Damage
Figure 13-6b
GTO’s
Figure 13-7
Movement
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Types of movement
Reflex
Voluntary
Rhythmic
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
CNS Integrates Movement
Table 13-3
CNS Control of Voluntary Movement
Figure 13-10
CNS Control of Voluntary Movement
• Feedforward reflexes and feedback of
information during movement
Figure 13-13
Parkinson’s Disease
• Progressive neural disorder
• Characterized by abnormal movements,
speech difficulties, and cognitive changes
• Loss of basal ganglia that release
dopamine
Visceral Movement
• Moves products in hollow organs
• Controlled by ANS
• Some create own action potentials
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
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