NSCI 201 Chapter Notes - Chapter 18: Pars Compacta, Medium Spiny Neuron, Saccade

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NSCI 201 (16.18)
Movement/ Basal Ganglia
15th March 2016
Movement and the Basal Ganglia!
!This lecture: Basal ganglia, does not make contact with lower circuit neurons, modulatory
role. Refer to 14.16 for organization of neural structures. !
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Motor components of the basal ganglia!
Note: Striatum (caudate and putamen), nucleus accumbens. !
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The basal ganglia is important for the facilitation of smooth, fine movements.!
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Anatomical organisation of inputs to the basal ganglia!
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The striatum (C/P) has dorsal and ventral portions: !
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Dorsal portions are important in motor function, ventral regions
more involved with limbic system. !
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Nearly all cortical association regions have projections to
striatum— this is highly anatomically precise in terms of
functional representation; cortical regions with similar function
will project to similar regions in the striatum. !
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Globus pallidus has internal and external regions.!
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Substantia nigra pars compacta is site of dopamine projections.!
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Idea: Projections form a set of parallel processing loops. !
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Information from cortex > subcortical regions (eg. Striatum) for
processing, > cortex!
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NSCI 201 (16.18)
Movement/ Basal Ganglia
15th March 2016
!
Neurons and circuits of the basal ganglia!
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Next step: going from the caudate and putamen into the globus pallidus!
Within caudate and putamen, there are cell regions called ‘patches’, surrounded by regions
called ‘matrix’. Patches: indirect pathway, receive limbic and prefrontal inputs, project to GPe!
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Matrix cells contain AChE, receive motor input, project to GPi, constituting the direct pathway.!
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Medium spiny neurons (MSNs) GABA-ergic, inhibitory effects. !
More about MSNs: Many spines, can integrate input from many cortical neurons while synapsing
with a few. Project to GPi, make diffuse connections with many, but strong connections with only
one GP neuron. (More MSNs than GP neurons)!
!
MSN function may be modulated by dopaminergic and local circuit neurons. !
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NSCI 201 (16.18)
Movement/ Basal Ganglia
15th March 2016
Functional organisation and intrinsic circuitry and outputs of the basal ganglia!
Direct and indirect loops from striatum; these integrate to affect motor function.!
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Direct: Striatum > GPi > VA of thalamus > frontal cortex. Mediates motor behaviour.!
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Indirect: Striatum > GPe > subthalamic nucleus > GPi. Inhibitory effects on direct pathway.!
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Separate pathway for eye movement: Striatum > substantia nigra pars reticulata > SCx!
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*Substantia nigra pars reticula is parallel to GPi!
!
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Nerve Cells in a disinhibitory circuit!!
Overall effects of a chain of neurons can flip.
(Study this diagram)!
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Basic concept: glutamate is excitatory (+),
GABA is inhibitory (-). When + is followed by -,
excitation of glutamate cell excites GABA cell,
causing greater inhibition. !
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GP is tonically active, transiently inhibited by
projections from striatum. (Recall: MSNs are
GABAergic)!
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