Download TSM60 - The Basal Ganglia

TSM60: BASAL GANGLIA
31/10/08
LEARNING OUTCOMES
Describe the anatomy of the basal ganglia
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The basal ganglia are five grey matter nuclei situated near the base of each cerebral hemisphere:
o Caudate – immediately lateral to the lateral ventricles
o Globus pallidus – immediately lateral to the internal capsule (inferior to the caudate)
o Putamen – lateral to the globus pallidus, with which it forms the lentiform nucleus
o Subthalamic – inferior to the thalamus
o Substantia nigra – inferior to the subthalamic
These nuclei receive various input signals from the cerebral cortex and give outputs to the thalamus
o Projections from the thalamus lead to the pre-frontal, pre-motor and primary motor cortices
o The cerebral cortex provides excitatory stimulation of the striatum using glutamate
o They do not receive somatosensory (spinal) inputs (compare to the cerebellum – see below)
Outline the role of the basal ganglia in the control of movement
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Like the cerebellum, the basal ganglia modify descending motor signals to control movement
o Unlike the cerebellum, the basal ganglia have outputs to the pre-frontal cortex
o They also receive inputs from the entire cortex i.e. are not limited to motor areas
In the resting state:
o The putamen and caudate are quiescent
o The globus pallidus is active
o The thalamus is inhibited such that it does not excite motor areas of the cortex
During movement:
o The putamen and caudate are active
o The globus pallidus is inhibited by the above
o The thalamus is uninhibited and so active allowing motor excitation of the cortex
Excitation of the subthalamic nucleus inhibits the globus pallidus and suppresses movement
The substantia nigra uses dopamine to excite the putamen and caudate to promote movement
Describe the major clinical effects of damage to the basal ganglia
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Damage to the basal ganglia generally results in:
o Dyskinesia – generalised difficulty in movement
o Bradykinesia – slowed movements
o Hypertonia – raised muscle tone and rigidity
Specific lesions to particular areas result in characteristic disorders:
o Chorea – rapid twitching movements of the limbs and face – damage to caudate
o Athetosis – slow writhing movements mostly of the hands – damage to putamen
o Tremor – involuntary movement at rest e.g. in Parkinson’s – damage to substantia nigra
o Hemiballismus – violent flailing movements – damage to subthalamic nucleus