Basal Ganglia

Question 1

Basal ganglia components

Answer 1

Striatum;
- Caudate nucleus
- Putamen

Globus pallidus
- Externa
- Interna

Substantia Nigra (SN) (Dopamine)

Subthalamic nucleus

Question 2

Connections

Answer 2

The striatum receives input from the SN, either inhibit or excitatory dependent on the receptors (D1 and D2)

Inhibitory: indirect route (D2)
- inhibits GPe
- Inhibits STN and GPi
- Inhibits thalamus
Effect: less movement

Excitatory: direct route (D1)
- Inhibits SNr
- Reduces inhibition in thalamus
- Excites the cortex
Effect: more movement

Question 3

Dam metaphor

Answer 3

From the cerebral cortex theres all possible actions that you can execute. You don’t want to get this all mixed up an overflow, so the basal ganglia forms a dam, a threshold

If a motor response is chosen, that ‘stream’ gets most active response, and therefore overcomes the threshold. Allowing that movement to pass.

In diseases related to the BG, the dam is too high or too low.
- Letting too many movements past: Huntington
- Or too little movements: Parkinson

Question 4

Parkinson

Answer 4

The SNc is not releasing dopamine, making the indirect pathway way stronger than the direct one.

Strong difficulty in initiating movement

Quite common, usually from 50+.
- Tremor of hands, brandykensia and rigidity (posture)

Medication: L-dopa, stemcells and Deep Brain Stimulation

Question 5

Huntington

Answer 5

The pathway between the striatum and GPe (D2) is damaged. Making the direct route a lot stronger than the indirect.

Result: hyperkinesia (chorea) too many movements.