CHAPTER 16Control of Posture & Movement 259each Purkinje cell receives inputs from 250,000 to 1 million
mossy fibers, but each has only a single climbing fiber from the
inferior olive, and this fiber makes 2000–3000 synapses on the
Purkinje cell. Climbing fiber activation produces a large, com-
plex spike in the Purkinje cell and this spike in some way pro-
duces long-term modification of the pattern of mossy fiber
input to that particular Purkinje cell. Climbing fiber activity is
increased when a new movement is being learned, and selective
lesions of the olivary complex abolish the ability to produce
long-term adjustments in certain motor responses.
CHAPTER SUMMARY
■ The ventral corticospinal tract and medial descending brain
stem pathways (tectospinal, reticulospinal, and vestibulospinal
tracts) regulate proximal muscles and posture. The lateral corti-
cospinal and rubrospinal tracts control distal limb muscles and
skilled voluntary movements.
■ Spinal cord transection is followed by a period of spinal shock
during which all spinal reflex responses are profoundly depressed.
■ Decerebrate rigidity leads to hyperactivity in extensor muscles
in all four extremities; it is actually spasticity due to facilitation
of the myotatic stretch reflex. Decorticate posturing or decorti-
cate rigidity is flexion of the upper extremities at the elbow and
extensor hyperactivity in the lower extremities.
■ The basal ganglia include the caudate nucleus, putamen, globus
pallidus, subthalamic nucleus, and substantia nigra. The connec-
tions between the parts of the basal ganglia include a dopaminergic
nigrostriatal projection from the substantia nigra to the striatum
and a GABAergic projection from the striatum to substantia nigra.
■ Parkinson disease is due to degeneration of the nigrostriatal do-
paminergic neurons and is characterized by akinesia, bradykin-
esia, cogwheel rigidity, and tremor at rest. Huntington disease is
characterized by choreiform movements due to the loss of the
GABAergic pathway to the globus pallidus.
■ The cerebellar cortex contains five types of neurons: Purkinje,
granule, basket, stellate, and Golgi cells. The two main inputs to
the cerebellar cortex are climbing fibers and mossy fibers.
Purkinje cells are the only output from the cerebellar cortex and
they generally project to the deep nuclei.
■ Damage to the cerebellum leads to several characteristic abnor-
malities, including hypotonia, ataxia, and intention tremor.MULTIPLE-CHOICE QUESTIONS
For all questions, select the single best answer unless otherwise directed.
- A primary function of the basal ganglia is
A) sensory integration.
B) short-term memory.
C) planning voluntary movement.
D) neuroendocrine control.
E) slow-wave sleep.
2. The therapeutic effect of L-dopa in patients with Parkinson dis-
ease eventually wears off because
A) antibodies to dopamine receptors develop.
B) inhibitory pathways grow into the basal ganglia from the
frontal lobe.
C) there is an increase in circulating α-synuclein.
D) the normal action of nerve growth factor (NGF) is dis-
rupted.
E) the dopaminergic neurons in the substantia nigra continue
to degenerate.
3. Increased neural activity before a skilled voluntary movement is
first seen in the
A) spinal motor neurons.
B) precentral motor cortex.
C) midbrain.
D) cerebellum.
E) cortical association areas.
4. After falling down a flight of stairs, a young woman is found to
have partial loss of voluntary movement on the right side of
her body and loss of pain and temperature sensation on the left
side below the midthoracic region. It is probable that she has a
lesion
A) transecting the left half of the spinal cord in the lumbar
region.
B) transecting the left half of the spinal cord in the upper tho-
racic region.
C) transecting sensory and motor pathways on the right side of
the pons.
D) transecting the right half of the spinal cord in the upper tho-
racic region.
E) transecting the dorsal half of the spinal cord in the upper
thoracic region.
5. Patients with transected spinal cords frequently have a negative
nitrogen balance because
A) they develop hypercalcemia, and this causes dissolution of
the protein in bone.
B) they are paralyzed below the level of the transection.
C) they lack the afferent input that normally maintains growth
hormone secretion.
D) they have difficulty voiding, and this causes nitrogen to
accumulate in the urine in the bladder.
E) their corticotropin response to stress is reduced.
6. Which of the following diseases is not known to be caused by
overexpression of a trinucleotide repeat?
A) Alzheimer disease
B) Fragile X syndrome
C) Spinocerebellar ataxia, type 3
D) Huntington disease
E) Friedreich ataxia
CHAPTER RESOURCES
Alexi T, et al: Neuroprotective strategies for basal ganglia
degeneration: Parkinson’s and Huntington’s diseases. Prog
Neurbiol 2000;60:409.
De Zeeuw CI, Strata P, Voogd J: The Cerebellum: From Structure to
Control. Elsevier, 1997.
Ditunno JF Jr, Formal CF: Chronic spinal cord injury. N Engl J Med
1994; 330:550.