Direct & Indirect Basal Ganglia Pathways

Question 1

Does the direct pathway stimulate or inhibit movement?

Answer 1

Stimulate

Question 2

Which dopamine receptor does the direct pathway use?

Answer 2

D1

Question 3

Describe the direct pathway

Answer 3

• Cortex sends excitatory nerve fibres to the striatum (using glutamic acid)
• Striatum sends inhibitory nerves fibres to the GPi & SNpr (using GABA)
• GPi & SNpr are now inhibited.
• Therefore, GPi & SNpr’s inhibitory nerve fibres cannot inhibit the thalamus (using GABA).
• So, the thalamus is active and sends its excitatory fibres to the motor regions of the cortex (glutamic acid).
• Thus, initiating movement.

Question 4

Does the indirect pathway stimulate or inhibit movement?

Answer 4

Inhibit

Question 5

Which dopamine receptor does the indirect pathway use?

Answer 5

D2

Question 6

Describe the indirect pathway

Answer 6

• Cortex sends excitatory nerves fibres to the striatum (using glatmic acid).
• Striatum sends inhibitory nerves fibres to the GPe (using GABA).
• GPe is now inhibited.
• Therefore, GPe’s inhibitory nerve fibres cannot inhibit the thalamus (using GABA).
• Thus, the subthalamic nucleus is now active & sends its excitatory fibres to GPi & SNpr (using glutamic acid).
• The SNpr & GPi now send their inhibitory nerve fibres to the thalamus (using GABA).
• The thalamus is now inhibited and does not send its excitatory fibres to the more regions of the cortex.
• Thus, movement is inhibited.

Question 7

Which part of the substantia nigra has dopaminergic neurones?

Answer 7

Pars compacta

Question 8

What does dopamine do when it binds to D1 receptors?

Answer 8

It increases neuronal firing.

Question 9

What does dopamine do when it binds to D2 receptors?

Answer 9

It decreases neuronal firing.

Question 10

What would an increase of dopamine do to the direct and indirect pathways?

Answer 10

It would increase the activity of the direct pathway and decrease the activity of the indirect pathway.

Question 11

What happens in Parkinson’s in relation to the direct & indirect pathways?

Answer 11

• Underactivity of the direct pathway.
• Overactivity of the indirect pathway.
• THUS, difficulty initiating movement.