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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
What is contained in the striatum of the basal ganglia?
- caudate nucleus
- 95% of cells in striatum are medium spiny neurons (MSN)
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
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
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
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
What structures does the posterior limb of the internal capsule separate?
globus pallidus (GPi) from the thalamus, subthalmic nucleus & SNr
What structures does the anterior limb of the internal capsule separate?
caudate nucleus & thalamus from lentiform nucleus
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)
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)
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
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
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
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)
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
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
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.
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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