Lecture 20: Basal Ganglia

Question 1

Major input structure of the basal ganglia

Answer 1

1. Caudate nucleus
2. Putamen
3. Nucleus Accumbens

Question 2

Major cell types of input structures of basal ganglia

Answer 2

GABAergic

Question 3

Major output structures of the basal ganglia

Answer 3

1. Internal globus pallidus (GPi)
2. Substantia Nigra (SN)
3. Pars Reticulate (SNr)

Question 4

Major cell type of output structures of basal ganglia

Answer 4

GABAergic inhibitory

Question 5

What makes up the Corpus Striatum?

Answer 5

1. Nucleus Accumbens
2. Caudate
3. Putamen
4. Globus pallidus

Question 6

Only glutamatergic excitatory cells in basal ganglia

Answer 6

Subthalamic projection cells

Question 7

What gives dopaminergic input to the basal ganglia?

Answer 7

Substantia nigra pars compacta

Ventral tegmental Area

Question 8

What makes up the lenticular or lentiform nucleus?

Answer 8

Putamen and Globus Pallidus

Question 9

Loss of neurons in which area causes Parkinson’s Disease?

Answer 9

Pars Compacta

Question 10

Identify areas of the Basal Ganglia (Picture)

Answer 10

Question 11

What makes up the substantia nigra?

Answer 11

1. Pars Compacta
2. Pars Reticulate

Question 12

ID afferents of Basal Ganglia

Answer 12

Question 13

What part of the basal ganglia does the frontal lobe mostly project to?

Answer 13

Caudate head and putamen

Question 14

What part of the basal ganglia do the parietal and occipital lobes mostly project to?

Answer 14

Caudate body

Question 15

What part of the basal ganglia does the temporal lobe mostly project to?

Answer 15

Caudate tail

Question 16

What part of the basal ganglia do the primary motor and somatosensory cortices mostly project to?

Answer 16

Putamen

Question 17

What part of the basal ganglia does the limbic cortex mostly project to?

Answer 17

Nucleus accumbens

Question 18

Major output structures of the basal ganglia

Answer 18

1. Globus pallidus
2. Substantia nigra pars reticulata

GABAergic inhibitory cells

Question 19

What happens if you excite the direct pathway in the basal ganglia?

Answer 19

Excite thalamic neurons which excite cortical neurons

Question 20

What happens when you excite the indirect pathway of the basal ganglia?

Answer 20

Inhibit thalamic neurons which are then unable to excite motor cortex neurons

Question 21

General purpose of the direct pathway

Answer 21

Activates motor programs that are adaptive for the current task

Question 22

General purpose of the indirect pathway

Answer 22

Inhibits the execution of competing motor programs for the current task

Question 23

What happens when the balance between the direct and indirect pathways is upset?

Answer 23

Extrapyramidal Syndrome

Question 24

Describe the direct pathway

Answer 24

1. 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.
2. 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.
3. Because the GPi and SNr inhibition to the thalamus is now turned off the thalamus is free to…
4. Activate the cortex which…
5. 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.

Question 25

Describe the **indirect** pathway

Answer 25

1. 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. 2. 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. 3. EXCITATORY Subthalamic cells are now activated (released from inhibition) and project to and excite GABAergic cells in GPi (and SNr). 4. These activated GPi cells project to and restrict/reduce the amount of thalamic activation that was generated by the direct pathway thus… 5. Narrowing down/reducing the activated thalamic output to the cortex thus… 6. Generating a more select action by cortex.

Question 26

What dopamine receptors do the direct striatal neurons have?

Answer 26

D1; cells activated by dopamine

Question 27

What dopamine receptors do the indirect striatal neurons have?

Answer 27

D2; cells inhibited by dopamine

Question 28

What does the nigrostriatal pathway do overall?

Answer 28

Excites cortex in two ways: 1. Excites direct pathway 2. Inhibits indirect pathway

Question 29

What causes Parkinson's disease?

Answer 29

Loss of dopaminergic neurons in substantia nigra pars compacta

Question 30

What causes Huntington's Disease?

Answer 30

Selective loss of nerons in the indirect pathway

Question 31

Symptoms of Huntington's Disease

Answer 31

Involuntary writhing movements of extremities and face Balance is tipped in favor of direct pathway

Question 32

Cause of Hemiballism

Answer 32

Decrease in indirect pathway due to damage to the subthalamic nucleus

Question 33

Role of ACh in basal ganglia

Answer 33

1. Inhibit striatal cells of direct pathway 2. Excite striatal cells of the indirect pathway 3. Results in decrease of movement 4. Tourette's might be due to reduced ACh

Question 34

How does the basal ganglia affect response to rewards?

Answer 34

Nigrostriatal pathway fires in response to reward. Excites direct and inhibits direct pathway, strengthening behavior.