Motor control and disease pt 2

Question 1

Function of the basal ganglia and cerebellum

Answer 1

Influence movement indirectly by regulating function of upper motor neurons
- No direct connections to lower motor neurons

Question 2

Describe the motor loop

Answer 2

Motor cortex connects to basal ganglia
- Feedback to premotor area via ventrolateral complex of the thalamus (VLo)
- Controls the initiation of movement

Question 3

What are the key components in the initiation of movement?

Answer 3

• Motor cortex
• Basal ganglia (caudate, putamen, globus pallidus, subthalamic nucleus)
• Ventral lateral nucleus of thalamus (diencephalon)
• Substanitia nigra

Question 4

Describe the direct pathway of basal ganglia

Answer 4

1. GPi tonically inhibits the VLo
2. Input from many cortical regions converges on the striatum
3. Striatum inhibits the inhibitory activity of GPi, releasing VLo and activating area 6
   - This initiates movement

Question 5

Why is the direct pathway of basal ganglia set up like it is?

Answer 5

Integration of cortical inputs to trigger a response
Rapid response (inhibition of inhibition)

Question 6

Describe the indirect pathway of the basal ganglia

Answer 6

1. The substantia nigra acts via the striatum (CP) to maintain the balance between inhibition and activation
   - Excitatory input from SN stimulates VLo activation by activating inhibition of GPi via the direct pathway
   - GPe inhibits GPi via indirect
   - Inhibition input from SN decreases CP inhibition of GPe
   - GPi inhibition allows activation of VLo
2. SN balances activation of VLo

Question 7

What does degeneration in the indirect pathway result in?

Answer 7

Parkinson’s or Huntington’s disease

Question 8

What are the motor symptoms of Parkinson’s disease?

Answer 8

Hypokinesia - insufficiency of movement
Bradykinesia - slow movements
Akinesia - no movement
Resting tremor

Question 9

What is the cause of Parkinson’s?

Answer 9

Loss of Dopamine
- due to loss of dopaminergic neurons in the substantia nigra

Question 10

What is a therapy for Parkinson’s?

Answer 10

Intravenous L-DOPA
- Only lasts 5 years

Question 11

How does L-DOPA therapy work?

Answer 11

Boosts capacity of surviving DA-ergic neurons in SN to make DA
- Doesn’t prevent degeneration of SN neurons

Question 12

What are the effects of DA loss in the basal ganglia?

Answer 12

Increased activity of the indirect pathway
Decreased activity of direct pathway
- Less inhibition of GPi
- Decreased activity of VLo so less motor cortex activation

Question 13

Describe the symptoms of Huntington’s disease

Answer 13

Early :
- Hyperkinesia
- Dyskinesia
- Chorea
Late :
- Akinesia
- Dystonia
- Dementia

Question 14

What is the cause of Huntington’s disease?

Answer 14

Autosomal dominant genetic disease resulting in neuronal degeneration
- Initially in the indirect pathway (striatum)
- Subsequently in the direct pathway (GPe)

Question 15

Describe Huntington’s disease in the basal ganglia

Answer 15

Degeneration in the striatum reduces the indirect pathway inputs to GPe
- Increases inhibition of GPi
- Results that VLo is dis-inhibited so there is an inappropriate initiation of movement
Striatal direct path and GPe release to GPi to over-inhibit VLo

Question 16

Function of cerebellum

Answer 16

Sensory motor coordination and motor learning
- Movement is based on predictions of outcomes

Question 17

What is the primary function of the cerebellum loop with the motor cortex?

Answer 17

Detect and correct differences between intended movement and actual movement
- Motor error

Question 18

What do lesions in the cerebellum cause?

Answer 18

• Cerebellar ataxia
• Poorly integrated movement

Question 19

What is dyssynergia?

Answer 19

The ability to coordinate multiple muscles and joints in a sequence