Basal Ganglia

Question 1

What are the basal ganglia?

Answer 1

[a collection of structures classically associated with ‘extrapyramidal’ motor control. They include the telencephalic structures: caudate, putamen (caudate + putamen = neostriatum), globus pallidus, nu accumbens, a diencephalic structure: subthalamic nu, and a mesencephalic structure: substantia nigra.]

Question 2

What is the ‘direct’ pathway?

Answer 2

[specific corticostriatal cells excite (glutamate) a specific population of striatal neurons which inhibit (GABA) neurons of the inner sector of the globus pallidus. This suppresses (disinhibits) the tonic GABAergic inhibition on neurons of the VA/VL complex. As a result, behavior is ‘released’]

Question 3

What is the ‘indirect’ pathway?

Answer 3

[specific corticostriatal cells excite (glutamate) specific striatal neurons which inhibit (GABA) neurons in the external sector of the globus pallidus. This suppresses (disinhibits) tonic GABAergic inhibition on neurons of the subthalamic nucleus, which then start cranking and shoot glutamate (excitatory) at the GABAergic neurons of the inner sector of the globus pallidus. These neurons start cranking, shooting GABA at, and suppressing the activity of the thalamic neurons of the VA/VL complex. This suppression of thalamus suppresses behavior]

Question 4

What is the nigrostriatal pathway?

Answer 4

[The pathway that links the substantia nigra pars compacta (dopamine) with the striatum]

Question 5

Identify the axon trajectory between the inner sector of the globus pallidus and the VA/VL complex?

Answer 5

[Axons leaving the inner sector of the globus pallidus divide into the ansa lenticularis which dives under the subthalamic nucleus and the lenticular fasciculus, which separates the subthalamic nucleus from the zona incerta. They then merge as the thalamic fasciculus before moving rostral to the VA/VL complex.]

Question 6

Numerically, which input into the basal ganglia is most numerous?

Answer 6

[cortex (corticostriatal). The thalamus, including VA/VL complex and centromedian/parafasciular nuclei also make substantial contribution, but we tend to downplay that and play-up the corticostriatal input]

Question 7

Identify the parallel ‘loops’ associated with the basal ganglia?

Answer 7

[We concentrate on the ‘big 3’: motor, cognitive, limbic. The motor loop is input from motor and premotor cortex to putamen, to globus pallidus to the VA/VL complex. From VL, fibers target premotor cortex. The cognitive loop is from broad areas of parietal, temporal and prefrontal cortex to caudate to globus pallidus to VA/VL complex and into mediodorsal thalamus to broad areas of prefrontal cortex. The limbic loop is from amygdala, cingulate and other limbic cortical areas to ventral striatum (nu accumbens) to subtantia innominata (its ‘pet’ pallidal segment) to mediodorsal thalamus to prefrontal cortex, amygdala, and cingulate cortex].

Question 8

What is the transmitter used by projection cells of the striatum, globus pallidus and substantia nigra pars reticulata?

Answer 8

[GABA]

Question 9

What is the transmitter of the corticostriatal cells?

Answer 9

[glutamate]

Question 10

Regarding the basal ganglia, what is the source of dopamine input?

Answer 10

[substantia nigra pars compacta]

Question 11

What is the transmitter used by projection cells of the subthalamic nucleus?

Answer 11

[glutamate]

Question 12

What is the striatum?

Answer 12

[the caudate + putamen]

Question 13

What is the lenticular nucleus?

Answer 13

[the putamen + the globus pallidus]

Question 14

Identify the source of dopamine for the ventral striatum (aka, nucleus accumbens)?

Answer 14

[ventral tegmental area]

Question 15

What structure is considered the ‘output’ structure of the basal ganglia?

Answer 15

[inner sector of the globus pallidus and substantia nigra pars reticulata].

Question 16

Identify the fiber bundles exiting the inner sector of the globus pallidus?

Answer 16

[the ansa lenticularis dips underneath the subthalamic nucleus, the lenticular fasciculus comes over the top of the subthalamic nucleus; both of the these bundles converge as the thalamic fasciculus and project to the VA/VL complex of thalamus]