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What are the basal ganglia and what are their functions?
- basal ganglia are subcortical structures that are interconnected with cerebral cortex in a series of (segregated) parallel loops
- basal ganglia consists of several subcortical nuclei
- each loop of the basal ganglia is associated with different cortical areas
- separately process signals for skeletomotor, oculomotor, associative, and limbic systems
- select cerebral cortical signs that are most appropriate for the current behavioral context
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What is contained in the striatum of the basal ganglia?
- caudate nucleus
- putamen
- 95% of cells in striatum are medium spiny neurons (MSN)
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Where is the putamen located in relation to the caudate nucleus?
- the putamen is lateral to the caudate nucleus and ventral to to the body of the caudate
- the rostral portion of the putamen is continuous with the head of the caudate nucleus
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What are the components of the basal ganglia?
- caudate nucleus
- lentiform nucleus (putamen + globus pallidus = putamen + (GPe + GPi))
- substantia nigra pars reticulata (SNr)
- subthalamic nucleus
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Where is the putamen in relation to the globus pallidus?
- the putamen is lateral to the globus pallidus
- i.e. the globus pallidus is medial to the putamen
- the exterior globus pallidus (GPe) is next to the putamen
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Where is the globus pallidus in relation to the thalamus?
- the globus pallidus is rostral and lateral to the thalamus
- the globus pallidus is separated from the thalamus by the posterior limb of the internal capsule
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What structures does the posterior limb of the internal capsule separate?
globus pallidus (GPi) from the thalamus, subthalmic nucleus & SNr
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What structures does the anterior limb of the internal capsule separate?
caudate nucleus & thalamus from lentiform nucleus
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Which structures are medial to the internal capsule? Which structures are lateral to the internal capsule?
- medial: caudate nucleus, thalamus, subthalamic nucleus, SNr
- lateral: lentiform nucleus (putamen + GPe + GPi)
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What are the input, intermediate, and output nuclei of the basal ganglia?
- input: caudate, putamen
- intermediate: GPe, subthalamic nucleus
- output: GPi (to thalamus), SNr (to thalamus and superior colliculus)
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For which parts of the basal ganglia does the GPi function as output nuclei? Where does the GPi project?
- the GPi functions as output nuclei for limb-related regions of the basal ganglia
- the GPi projects to the thalamus
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For which parts of the basal ganglia does the SNr function as output nuclei? Where does the SNr project?
- the SNr function as output nuclei for the eye-movement-related areas of the basal ganglia
- the SNr project to the thalamus and the superior colliculus
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What are the inputs and outputs of the subthalamic nucleus? What type of basal ganglia nucleus is this?
- inputs: GPe
- outputs: GPi and Snr
- type: intermediate nucleus
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What are the two kinds of major spiny neurons (MSN) in the striatum of the basal ganglia?
- 1. those that express D1 dopamine receptors; excited by dopamine (direct pathway)
- 2. those that express D2 dopamine receptors; inhibited by dopamine (indirect pathway)
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What does dopamine do to D1 and D2 receptors in the stiatum and how does this effect thalamocortical projections?
- dopamine stimulates D1 (direct pathway) and ultimately increases thalamocortical projections by decreasing their inhibition
- dopamine inhibits D2 (indirect pathway) and ultimately decreases thalalmocortical projections by increaseing their inhibition
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What are treatments for Parkinson's disease?
- L-dopa: replaces dopamine in striatum that has been diminished by SNc damage
- pallidotomy (i.e. permanent damage to GPi): reduces inhibitory input to thalamus from GPi
- electrical stimulation of subthalamic nucleus: mechanism unclear; reduces GPi inhibition of thalamus
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True or False: There is a paradoxical relationship between the subthalamic nucleus and the GPi: the subthalamic nucleus both stimulates it directly and also inhibits it indirectly, but the net effect is to reduce GPi projections.
True
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What are characteristics of Huntington's Disease?
- hyperkinetic disorder
- results from decreased inhibition of the thalamus --> increase in thalamocortical projections
- preferential degeneration of D2 medium spiny neurons in striatum (indirect pathway)
- enlarged ventricles
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