PD - Loops

Question 1

What are the BG loops

Answer 1

Decides how much inhibition to give to motor cortex

Over-inhibition –>Parkinsonism: ↓ limb mobility & ↑ trunk stability

Under-inhibition --> Dyskinesias: ↓ trunk stability & ↑ limb mobility
Tremor
Chorea
Athetosis
Hemiballismus

Question 2

Direct loop

Answer 2

Excitatory loop

Thalamus - modulates the motor cortex
The Globus Pallidus releases GABA which could potentially inhibit the thalamus from activating the motor cortex
Then you have the striatum which also releases GABA that inhibits the GP. Therefore the motor cortex gets more activated because the direct pathway is more positive.
(striatum inhibits the GP from inhibiting the thalamus, thereby exciting the motor cortex)

Question 3

Indirect Loop summary

Answer 3

Inhibitory Loop

Sub Thalamic Nuclei releases Glutamate which excites the Globus Pallidus, which then inhibits the Thalamus, making the Thalamus less excitatory (inhibitory) for the Motor Cortex

Question 4

Dopaminergic Pathway summary

Answer 4

Excitatory

Substantia Nigra releases Dopamine which excites Striatum, inhibiting GP which increases Direct Loop.
SN inhibits the GP, decreasing the indirect loop. Both actions = Motor Cortex Excitation

Question 5

Which loop are we running on in PD

Answer 5

With PD there is less dopamine –> pretty much running on a indirect loop
–> that is why with PD we see less motor output, it is very inhibited

Question 6

If you have over inhibition this leads to

Answer 6

PD - limbs move less and trunk becomes more stable

Question 7

If you have under inhibition

Answer 7

leads to over excitation which means you have to much dopamine this leads to Dyskinesias
–> Trunk less stable and limbs more mobile
Seen in Huntington’s Disease