26 Basal Ganglia & Cerebellum

26 Basal Ganglia & Cerebellum - PSL302: Lecture 26,...

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Basal Ganglia & Cerebellum - Not in line w/ programming afferents: i.e. brainstem, spinal cord, cortex Basal ganglia - Medial frontal lobe: supplementary + cingulate motor areas - Process internal drives: memory sources for mvt + sensory cues - Regulated by basal ganglia -> essential for mvt - Regulates Fow of volitional drive to premotor centers - Deep inside cerebral hemispheres around lateral ventricles - Divided into 2 tiers of nuclei , collectively known as striatum (input) and pallidum (output) - Striatum: topographic input from cerebral cortex + thalamus (CM nucleus) - Diagram: darkly shaded, outer layer of nuclei, divided by band of white matter - CM nucleus of thalamus: spinoreticulothalamic tract (postural) terminates at striatum - Pallidum: projects output to premotor centers - Inner layer of basal ganglia - Portion in substantia nigra separated by band of white matter Pallidum - Neurons are tonically discharging (active) - Inhibit premotor nuclei in thalamus, sup. colliculus (eye-head mvts), mesencephalic locomotory region (use GABA) - Tonically suppresses motor programs - In order to initiate a speci±c mvt, a speci±c premotor center is disinhibited - Speci±c actions assoc w/ envmtal cues : not always performing them - If you didn’t have any inhibition, you would be always performing them! - Also regulates speed of mvt Premotor disinhibition - Accomplished by inhibiting pallidal neurons - Striatum projects to pallidum and inhibits pallidal neurons (using GABA) - Therefore, activation of a speci±c locus in striatum can enable motor program by removing tonic inhibition Diagram: Striatum action on pallidum - Striatum gathers signals from cerebral cortex: looks at diff combos of inputs - When suitable # inputs activated, burst of ±ring -> project into pallidum (green circle) - Learn patterns when to make appropriate mvts - Pallidum has high background discharge (tonic inhibition) - Permissive role: striatum silences pallidum = disinhibition of premotor centers = activate mvt Basal Ganglia inhibition disinhibition CPG PSL302: Lecture 26, by Prof. MacKay Wed., Nov. 17, 2010 1 of 6
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Striatal modulation - Specifc neurons in substantia nigra (SN) contain dopamine (project back to striatum) - Facilitate striatopallidal projection neurons: transFer oF inFo to pallidum - Enhances plasticity = enhances learning - Dopamine released where activity is high in pallidum - Striatum chooses motor act to perForm at any instant, guided by cortical + reticular inputs - SN dopaminergic system plays a key role in determining active part oF striatum Diagram: Two pathways connecting striatum + pallidum - Direct: inhibitory pathway From striatum -> pallidum
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26 Basal Ganglia & Cerebellum - PSL302: Lecture 26,...

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