Anatomy and function of basal ganglia

Question 1

Striatum

Answer 1

Composed of the caudate nucleus and putamen

Question 2

Structures of the basal ganglia

Answer 2

Caudate nucleus

Lentiform:

• Putamen
• Globus pallidus [internal and external segment]

Question 3

Neostriatum

Answer 3

Composed of:

• Caudate nucleus
• Putamen

Motor function

Question 4

Function of basal ganglia

Answer 4

Interfaces with the cortex

• Organises the possible inputs from the cortex
• Gates the proper initiation of movement

Question 5

Direct movement loop [4]

Answer 5

This loop promotes action:

1. Cortex excites the striatum, using GLU
2. Excited striatum is able to send inhibitory signals to the Internal Globus Pallidus [GPi] , via GABA
3. Inhibitory signals to the GPi supresses its activity.
   - Prevents inhibitory signals being sent to the thalamus. [disinhibition of thalamus]
4. Thalamus is able to be excited and send excitatory signals to the cortex.

Question 6

Indirect movement loop

Answer 6

This loop inhibits action

1. Cortex sends excitatory signals to the striatum, via GLU
2. Excited striatum is able to send inhibitory signals to the External Globus Pallidus [GPe]
   - Decreases activity of GPe
3. Decreased activity of the GPe allows excitation of the Subthalamic nucleus [STN]
4. Excited STN sends excitatory signals to the GPi
   - GPi activity increased
5. Excited GPi is able to send inhibitory signals to the thalamus
   - Thalamic activity is decreased
6. Thalamus is unable to send excitatory signals to the cortex
   - Cortex is not excited

Question 7

Hyperdirect pathway of movement

Answer 7

Stops movement very quickly

1. Cortex excites the subthalamic nucleus [STN]
2. Increased activity of the STN allows for the excitation of the GPi
   - GPi is active
3. Active GPi is able to send inhibitory signals to the thalamus
   - Thalamic activity is depressed
4. Thalamus is unable to send excitatory signals to the cortex

This loop bypasses the striatum

Question 8

Medium spiny neurones

Answer 8

Motor striatal cells with dopamine receptors

Two groups:
- One contains dopamine-1 receptors [D1] which stimulates excitation
= direct pathway

• Another group contains dopamine-2 receptors [D2] which has inhibitory outputs
  = indirect pathway

Question 9

Striatum interneurons

Answer 9

Use acetylcholine
- Modulates dopamine release

Acting on medium spiny neurones [MSN] with D1 receptors
= inhibits effects of DA
= inhibits direct pathway
= inhibits movement

Acting on MSN with D2 receptors
= increases excitation
= stimulates indirect pathway
- prevents movement

Question 10

Balance of direct and indirect pathways

Answer 10

The likelihood of movement taking place is determined by the balance of activity between the medium spiny neurones

Dopamine and acetylcholine regulate this balance

Also influenced by the cortical inputs to the striatum

Question 11

Substantial nigra

Answer 11

Nucleus that produces dopamine

Projects into the striatum