The Two Key Parts of the Basal Ganglia
- Striatum
- Pallidum
At Rest
- The pallidum is constantly active, inhibiting movement (represented on a graph as all possible movements being inhibited).
Initiating Movement
- The striatum receives excitatory input from the cerebral cortex (e.g., seeing a friend and wanting to smile).
- This excitatory input disinhibits the pallidum, specifically the movement pathway related to the desired action (smiling).
- This “inhibition of inhibition” allows the chosen movement to occur.
Direct Pathway
- This pathway is responsible for selecting and releasing a desired movement.
- Once a movement is released, it becomes the preferred movement and is harder to stop or change (behavioral inertia).
Indirect Pathway
- This pathway suppresses competing movements while the direct pathway is active.
- It ensures that only the chosen movement is happening and unnecessary movements are inhibited.
Disorders of the Basal Ganglia
- Parkinson’s disease: Dysfunction in the direct pathway leads to difficulty initiating movement (poverty of movement).
- Hemiballismus and Huntington’s chorea: Dysfunction in the indirect pathway leads to uncontrollable extra movements.
