Lecture 20: Basal Ganglia Flashcards
Major input structure of the basal ganglia
- Caudate nucleus
- Putamen
- Nucleus Accumbens
Major cell types of input structures of basal ganglia
GABAergic
Major output structures of the basal ganglia
- Internal globus pallidus (GPi)
- Substantia Nigra (SN)
- Pars Reticulate (SNr)
Major cell type of output structures of basal ganglia
GABAergic inhibitory
What makes up the Corpus Striatum?
- Nucleus Accumbens
- Caudate
- Putamen
- Globus pallidus
Only glutamatergic excitatory cells in basal ganglia
Subthalamic projection cells
What gives dopaminergic input to the basal ganglia?
Substantia nigra pars compacta
Ventral tegmental Area
What makes up the lenticular or lentiform nucleus?
Putamen and Globus Pallidus
Loss of neurons in which area causes Parkinson’s Disease?
Pars Compacta
Identify areas of the Basal Ganglia (Picture)
What makes up the substantia nigra?
- Pars Compacta
- Pars Reticulate
ID afferents of Basal Ganglia
What part of the basal ganglia does the frontal lobe mostly project to?
Caudate head and putamen
What part of the basal ganglia do the parietal and occipital lobes mostly project to?
Caudate body
What part of the basal ganglia does the temporal lobe mostly project to?
Caudate tail
What part of the basal ganglia do the primary motor and somatosensory cortices mostly project to?
Putamen
What part of the basal ganglia does the limbic cortex mostly project to?
Nucleus accumbens
Major output structures of the basal ganglia
- Globus pallidus
- Substantia nigra pars reticulata
GABAergic inhibitory cells
What happens if you excite the direct pathway in the basal ganglia?
Excite thalamic neurons which excite cortical neurons
What happens when you excite the indirect pathway of the basal ganglia?
Inhibit thalamic neurons which are then unable to excite motor cortex neurons
General purpose of the direct pathway
Activates motor programs that are adaptive for the current task
General purpose of the indirect pathway
Inhibits the execution of competing motor programs for the current task
What happens when the balance between the direct and indirect pathways is upset?
Extrapyramidal Syndrome
Describe the direct pathway
- The cerebral cortex provides a massive excitatory input to GABAergic cells in striatum (caudate, putamen and ventral striatum) activating them and causing them to fire.
- These activated inhibitory striatal cells project to and turn off the inhibitory GABAergic output cells of the basal ganglia in GPi and SNr who had been actively inhibiting the thalamus.
- Because the GPi and SNr inhibition to the thalamus is now turned off the thalamus is free to…
- Activate the cortex which…
- Generates an action!! Thus, because of the “double negative” in the pathway between the striatum and GPi and the GPi and thalamus, the net result of exciting the direct pathway striatal neurons is to excite cortex and generate an action.
Describe the indirect pathway
- Like step one in the direct pathway, the cerebral cortex also provides an excitatory input to ANOTHER SET of GABAergic cells in striatum (caudate, putamen and ventral striatum) activating them and causing them to fire.
- These activated inhibitory striatal cells project to and turn off the inhibitory GABAergic in external globus pallidus (GPe) that had previously been actively inhibiting cells in the subthalamic nucleus.
- EXCITATORY Subthalamic cells are now activated (released from inhibition) and project to and excite GABAergic cells in GPi (and SNr).
- These activated GPi cells project to and restrict/reduce the amount of thalamic activation that was generated by the direct pathway thus…
- Narrowing down/reducing the activated thalamic output to the cortex thus…
- Generating a more select action by cortex.
What dopamine receptors do the direct striatal neurons have?
D1; cells activated by dopamine
What dopamine receptors do the indirect striatal neurons have?
D2; cells inhibited by dopamine
What does the nigrostriatal pathway do overall?
Excites cortex in two ways:
- Excites direct pathway
- Inhibits indirect pathway
What causes Parkinson’s disease?
Loss of dopaminergic neurons in substantia nigra pars compacta
What causes Huntington’s Disease?
Selective loss of nerons in the indirect pathway
Symptoms of Huntington’s Disease
Involuntary writhing movements of extremities and face
Balance is tipped in favor of direct pathway
Cause of Hemiballism
Decrease in indirect pathway due to damage to the subthalamic nucleus
Role of ACh in basal ganglia
- Inhibit striatal cells of direct pathway
- Excite striatal cells of the indirect pathway
- Results in decrease of movement
- Tourette’s might be due to reduced ACh
How does the basal ganglia affect response to rewards?
Nigrostriatal pathway fires in response to reward. Excites direct and inhibits direct pathway, strengthening behavior.
