The Basal Nuclei And Motor Control Flashcards
What are the basal nuclei
A collection of nuclei deep to the white matter of cerebral cortex
Also called cerebral nuclei
Masses of gray matter
Are embedded in white matter
What are the basal nuclei composed of
Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus
Substantia Nigra
Much of the output of the basal nuclei which is mediated through the …… is to ….. the …… to the cerebral cortex
Thalamus is to reduce or dampen the excitatory input to the cerebral cortex
The basal nuclei provide a …….. off which ….. can be made
Postural platform off which purposeful movement can be made
When discharge patterns of BN are excessive, there is…
An abnormal slowing of movements
If there is a reduced output….
Abnormal involuntary movements occur at periods of rest (dyskinesia)
Basal nuceli encode for
Decision to move, direction of movement, amplitude of movement, motor expression of emotions
Input to the basal nuclei
Input to the striatum
Putamen - micromary motor area, secondary motor areas primary somatosensory area
Caudate nucleus - association areas, frontal eye fields, limbic system
Input enables…
BN to integrate info from multiple sources
Out put from the basal nuclei
Output from the globus pallidus interna (medial)
Via GABA-ergic neurons
To the thalamus
Thalamus under tonic inhibiton
Overall output from thalamus is excitatory to the cortex
Strength of thalamic signal dependent on GPi
Output from BN is …
Highly regulated
Balance of ……. To the thalamus
Inhibitory and excitatory pathways to the thalamus
Thalamus is under …… and BN either ……
Tonic inhibiton and basal nuclei either increase or decrease this inhibiton
Caudate nucleus
GABA - inhibitory
Putamen
GABA - inhibitory
Globus pallidus interna and externa
GABA - inhibitory
Subthalamic nucelus
Glutamate - Excitatory
Substantia nigra
Dopamine
Excitatory and inhibitory
Describe the basal nuceli circuit
• Striatum receives input from cortical areas inputs are roughly topographical (multiple parallel circuits)
• GPi/SNr are the major output nuclei
• Output is inhibitory
• Gpi/SNr neurons have high baseline firing rates (baseline = inhibition)
• Gpi/SNr input from the striatum is focal and inhibitory, whereas input from the STN is diffuse and excitatory
• Direct vs. indirect striatal pathways have opposing effects (inhib. vs. excit.)
• Output of thalamus is primary to motor areas
What are the 2 internal circuits of the basal nuclei
Direct pathway and indirect pathway
Describe the direct pathway and how it influences the thalamus
The wiring in this circuit releases the thalamus from its tonic inhibiton leading to more excitation of the cortex and in turn more cortical output
Describe the indirect pathway and how this influences the thalamus
The wiring in this circuit inhibits the output from the thalamus leading to less excitation of the cortex and in turn less cortical output
The indirect pathwa suppresses superfluous behaviours that are not related to targeted behaviour
Indirect and direct pathway together …
Influence the thalamus and ultimately streamline behavioural output
Describe SNc involvement in direct pathway
SNc sends dopaminergic connections to Putamen, that synapse onto excitatory D1 receptors. This effect is similar to excitation by cortex
This excites the inhibitory connections from putamen to Gpi and SNr, high, in turn releases VL from inhibiton to allow cortex excitation
Describe the overall direct pathway
- Excitatory projections from the cortex to the striatum synapse with the inhibitory neurons
- Inhibitory Enron’s project directly to the GPi
- From the GPi, inhibitory neurons project to the thalamus
- Inhibiton of the inhibiton releases the tonic inhibitory of the thalamus resulting in increased output
- The thalamus then sends excitortatory fibres to the cortex
- STN provides tonic stimulation to the SN, influencing output from the SN
- SN enhances the excitatory input from the cortex
Describe the indirect pathway overall
- Excitatory projections from the cortex to the stratum synapse with inhibitory neurons
- Dopaminergc neurons inhibit (via D2 receptors) excitatory cholinergic Interneurons in the striatum
- Inhibitor neurons project to the GPe
- From the GPe, an inhibitor projection goes to the STN
- The STN in turn sends an excitatory projection to the globus pallidus internal segment (GPi). This excites the inhibitory neurons in the GPi
- This excitation of the inhibition by the STN projection increases he tonic inhibition of the thalamus
- The thalamus then sends excitatory fibres to the cortex
Parkinson’s disease and pathways
Decr output of the SNc dopaminergic projections
Decrease inhibiton in direct pathway
Increase excitation in indirect pathway
Net effect: more inhibiton of thalamus and therefore less excitatory input to motor cortex
What happens in Parkinson’s - direct pathway
Less excitation from SNc to putamen
Less inhibiton of GPi and SNr
More tonic inhibiton of VL
Less excitation of cortex
What happens in Parkinson’s - indirect pathway
Less dopamine released on inhibitory D2 receptors more inhibiton from putamen to GPe
Less inhibiton from GPe to STN
More excitation from STN to GPi and SNR
More inhibiton from GPi and SNR to VL of thalamus
Less excitation of cortex
What happens in Huntington’s disease
Cell loss in the striatum that seems to affect the indirect pathway disproportionately
Net effect: less inhibiton of the thalamus and therefore excessive excitation of the motor cortex
