Control of Body Movement
313
3. Picking up a book, for example, has both voluntary and
involuntary components. List the components of this action
and indicate whether each is voluntary or involuntary.
4. List the inputs that can converge on the interneurons active in
local motor control.
5. Draw a muscle spindle within a muscle, labeling the spindle,
intrafusal and extrafusal muscle fi bers, stretch receptors,
afferent fi bers, and alpha and gamma efferent fi bers.
6. Describe the components of the knee jerk refl ex (stimulus,
receptor, afferent pathway, integrating center, efferent pathway,
effector, and response).
7. Describe the major function of alpha-gamma coactivation.
8. Distinguish among the following areas of the cerebral cortex:
sensorimotor, primary motor, premotor, and supplementary
motor.
9. Contrast the two major types of descending motor pathways in
terms of structure and function.
10. Describe the roles that the basal nuclei and cerebellum play in
motor control.
11. Explain how hypertonia might result from disease of the
descending pathways.
12. Explain how hypotonia might result from lower motor neuron
disease.
13. Explain the role the crossed-extensor refl ex plays in postural
stability.
14. Explain the role of the interneuronal networks in walking,
incorporating in your discussion the following terms:
interneuron, reciprocal innervation, synergist, antagonist, and
feedback.
e. Afferent neurons to the sensorimotor cortex stimulate
the agonist muscle to contract and the antagonist
muscle to be inhibited.
3. Which would result in refl ex contraction of the extensor
muscles of the right leg?
a. stepping on a tack with the left foot
b. stretching the fl exor muscles in the right leg
c. dropping a hammer on the right big toe
d. action potentials from Golgi tendon organs in extensors of
the right leg
e. action potentials from muscle-spindle receptors in fl exors of
the right leg
4. If implanted electrodes were used to stimulate action
potentials in gamma motor neurons to fl exors of the left arm,
which would be the most likely result?
a. inhibition of the fl exors of the left arm
b. a decrease in action potentials from muscle-spindle
receptors in the left arm
c. a decrease in action potentials from Golgi tendon organs in
the left arm
d. an increase in action potentials along alpha motor neurons
to fl exors in the left arm
e. contraction of fl exor muscles in the right arm
akinesia
307
autism
308
bradykinesia
307
cerebellar disease
307
clasp-knife phenomenon
309
Clostridium tetani
311
cramp
309
fl accid
310
hypertonia
309
hypotonia
309
intention tremor
307
Levodopa (L-dopa)
307
lockjaw
311
Parkinson’s disease
307
rigidity
309
spasm
309
spasticity
309
tetanus
297
upper motor neuron
disorder
309
CLINICAL TERMS
Chapter 10 Test Questions
(Answers appear in Appendix A.)
1. Which is a correct statement regarding the hierarchical
organization of motor control?
a. Skeletal muscle contraction can only be initiated by neurons
in the cerebral cortex.
b. The basal nuclei participate in the creation of a motor
program that specifi es the pattern of neural activity required
for a voluntary movement.
c. Neurons in the cerebellum have long axons that synapse
directly on alpha motor neurons in the ventral horn of the
spinal cord.
d. The cell bodies of alpha motor neurons are found in the
primary motor region of the cerebral cortex.
e. Neurons with cell bodies in the basal nuclei can either form
excitatory or inhibitory synapses onto skeletal muscle cells.
2. In the stretch refl ex:
a. Golgi tendon organs activate contraction in extrafusal
muscle fi bers connected to that tendon.
b. Lengthening of muscle-spindle receptors in a muscle leads
to contraction in an antagonist muscle.
c. Action potentials from muscle-spindle receptors in a muscle
form monosynaptic excitatory synapses on motor neurons to
extrafusal fi bers within the same muscles.
d. Slackening of intrafusal fi bers within a muscle activates
gamma motor neurons that form excitatory synapses with
extrafusal fi
bers within that same muscle.
sensorimotor cortex
304
somatosensory cortex
304
somatotopic map
304
stretch refl ex
302
substantia nigra
307
supplementary motor cortex
304
synergistic muscle
302
upper motor neurons
309
voluntary movement
299
withdrawal refl ex
303
REVIEW QUESTIONS
1. Describe motor control in terms of the conceptual motor
control hierarchy. Use the following terms: highest, middle,
and local levels; motor program; descending pathways; motor
neuron.
2. List the characteristics of voluntary actions.
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