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Basal ganglia
Chapter 56
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Motor Control by the Basal Ganglia
The BG are the five interactive structures on each side of the brain:
Caudate nucleus
nucleus, putamen,
putamen globus pallidus,
pallidus and amygdal.
amygdal
Associated nuclei:
 VA & VL nuclei
l i off thalamus,
h l
 Subthalamic nucleus of the diencephalon,
 Substantia nigra of the midbrain.
The main function:
Influence the motor cortex via pathways through the thalamus.
The role:
Aid in planning and execution of smooth movements.
Change the timing and scale the intensity of movement .
BG also contribute to affective and cognitive functions.Dr. Z Akbari
Organization of the basal ganglia
1- Caudate nucleus Striatum: major recipient of input from cortex,
2- Putamen
2
BS, thalamus.
3- Globus pallidus (Int, Ext) Major output projection…VA &VL of thalamus
4- Substantia nigra
g
…..to Sup Colliculus….eye movement
5 Subthalamic
5S bth l i nucleus
l
 With the exception of the primary visual and auditory cortices, most regions of the
cerebral cortex project topographically to the striatum.
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The basal ganglia in relation to surrounding structures
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Neural circuitry of the basal ganglia
cerebral cortex ……. Striatum,……..
GPi,………
GPi
,……… thalamus,……back to the
cortex.
The output from GPi to the thalamus
is inhibitory, whereas the output from
the thalamus to the cerebral cortex is
excitatory.
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Direct & indirect pathways through the
b
basal
l ganglia
li
• Direct pathway
(Excitatory)
Cortex
+
Striatum
GPi
Thalamus
• IIndirect
di t pathway
th
(Inhibitory)
Cortex
+
Striatum
GPe
STN
+
GPi
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Thalamus
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Some movement disorder result from imbalances
in the direct & indirect pathways in the BG
• Hypokinetic disorder
 Hyperkinetic disorder
•
 Excessive motor activity
•
Impaired initiation of movement
(akinesia
akinesia))
Reduced amplitude & velocity of
voluntary movement
( Bradykinesia
Bradykinesia))
•
Muscular rigidity(
g y( resistance to
passive displacement)
•
Tremor
•
Parkinson Dx
 Involuntary movement( dyskinesia)
dyskinesia)

muscle tone( hypotonia
hypotonia))
 Athetosis: slow, writhing
movements of extremities
 Hemiballismus: violent largelargeamplitude movement of proximal
limb( ballistic movement)
 Chorea: rapid & irregular writhing of
limb and orofacial structures
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 Huntington
Parkinson disease
The first example of a brain disorder from deficiency of a single neurotransmitter
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Parkinson Treatment:
 L - DOPA
 L – Deprenyl (MAOI)
 Surgical
S i l iintervention
t
ti
Dr. Z Akbari
Dr. Z Akbari
Lesions of subthalamic nucleus ……… ballism
(involuntary, often violent, movements of the contralateral limbs )
Hemiballism result from disinhibition of the thalamus due to reduction in the
tonic (and perhaps phasic)
phasic) output from the GPi………
GPi……… permit thalamocortical
neurons to respond in an exaggerated manner to cortical or other inputs
inputs.
OR
Increase the tendency of these neurons to discharge spontaneously, leading
t involuntary
to
i
l t
movements
t
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Huntington’s disease





Autosomal dominant
Age of onset: 30
30--50
Abnormal gene on chromosome 4
Loss of intrastriatal GABA
GABA--ergic and cholinergic neuron
Symptom:
 Hyperkinetic choreiform movement , dementia
 Death 10
10--15 y
years after onset of symptom
y p
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Difference between the basal ganglia and
cerebellar motor loop
 BG receive input from most areas of the cortex
 BG output from the BG is more widespread (Prefrontal &
premotor areas)
 BG do not receive somatosensory information from
ascending pathways in the SC & few connection with the
brain stem nuclei
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Integration of motor control systems
 Spinal level
 Hindbrain level
 Cortical level
 Associated function of the cerebellum and Basal Ganglia
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The end
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