Basal Ganglia

Question 1

Components of the basal ganglia

Answer 1

Caudate 
Putamen 
Globus Pallidus
Substantia Nigra
Subthalamic Nucleus

Question 2

What is the signaling path through the putamen?

Answer 2

Sensori-motor cortex projects to the putamen; putamen projects to the globus pallidus, which projects to VA thalamus; VA thalamus projects back to supplementary motor area of the cortex

Question 3

What is the signaling path through the caudate?

Answer 3

The caudate receives input from the frontal association cortex and sends axons to the globus pallidus; the globus pallidus then projects to the DM thalamus, which projects widely to association cortex

Question 4

Nucleus Accumbens

Answer 4

The caudal juncture between caudate and putamen

Question 5

Describe the Major Direct Pathway of signaling through the basal ganglia

Answer 5

Excitatory input to the caudate and putamen comes from the cerebral cortex; caudate and putamen send inhibitory projections to the globus pallidus, which sends inhibitory projections to the thalamus; thalamus sends excitatory fibers to the cortex

Main effect is to release inhibition of thalamo-cortical input, allowing initiation of movement

Question 6

Describe the signaling loop through the substantia nigra

Answer 6

Receives inhibitory input from striatum

Sends excitatory dopaminergic fibers back to the striatum, as well as inhibitory outputs to the thalamus

Question 7

Describe the signaling loop through the subthalamic nucleus

Answer 7

Receives inhibitory input from the globus pallidus externa

Projects excitatory output to the globus pallidus interna

Question 8

Pars compacta

Answer 8

Excitatory dopaminergic fibers projecting from the substantia nigra back to the striatum

Question 9

Pars reticulata

Answer 9

Inhibitory fibers projecting from the substantia nigra to the thalamus

Question 10

Describe the indirect pathway of signaling through the basal ganglia

Answer 10

Excitatory input to the caudate and putamen comes from the cerebral cortex; caudate and putamen send inhibitory projections to the globus pallidus externa, which sends an extra inhibitory projection to the subthalamic nucleus; the subthalamic nucleus sends an excitatory projection to the globus pallidus interna, which sends inhibitory projection to the thalamus

Main effect is to provide negative feedback of thalamo-cortical input, inhibiting initiation of movement

Question 11

What is the role of dopamine signaling in the basal ganglia?

Answer 11

Dopamine released from the substantia nigra is excitatory in the striatum; it increases the inhibition of the striatium onto the globus pallidus, allowing disinhibition of the globus pallidus onto the thalamus

End result is increased signaling of the thalamus to cerebral cortex to generate movement

Question 12

Pathogenesis of Huntington’s Disease

Answer 12

Degeneration of cholinergic and GABA-ergic medium spiny output neurons of the striatum, possibly as a result of glutamate excitotoxicity causing excessive influx of Ca2+ leading to cell death

Can also be caused by too much exogenous DOPA

Question 13

Hemiballismus

Answer 13

Flailing movements of the arm and leg on one side

Results form a stroke in a branch of the posterior cerebral artery leading to unilateral damage of the subthalamic nucleus; loss of excitation by the subthalamic nucleus reduces inhibitory outflow of globus pallidus onto thalamus, causing excessive motor program activity

Question 14

Where are deep brain stimulation electrodes placed in the treatment of Parkinson’s Disease?

Answer 14

In the subthalamic nucleus or internal segment of the Globus Pallidus; there, they release inhibition of thalamo-cortical input