Basal Ganglia

Question 1

What are the basal ganglia

Answer 1

Group of highly connected brain nuclei in forebrain involved in motor, cognitive and limbic functions

• caudate
• putamen
• globus pallidus

Question 2

Motor function of basal ganglia

Answer 2

1. Selecting appropriate movements
2. Imitating internally generated movements
3. Planning and execution of complex motor strategies

Question 3

Movement disorders of the basal ganglia

Answer 3

1. Tremor at rest
2. Chorea- involuntary movements
3. Rigidity- disorders of posture and muscle tones
4. Bradykinsia- slowness of movement
5. Akinesia- difficulty initiating movement

Question 4

Basal ganglia diseases

Answer 4

1. Parkinson’s (hypokinetic disorder)
   - loss of dopamine neurones in substantial nigra
2. Huntington’s (hyperkinetic)
   - primary pathology in striatum a corticospinal pathways
3. Ballismus (hyper)
   - results from damage to subthalamic nucleus

Question 5

Name all the inhibitory nuclei of the BG

Answer 5

1. Striatum
2. External Globus palludua (GPe)
3. Internal Globus pallidus (GPi)
4. Substantia nigra pars reticular (SNr)

Question 6

Where is dopamine produced in BG

Answer 6

Substantia nigra pars compacta (SNc)

Question 7

Cortical input to basal ganglia?

Answer 7

Cortico-striatal pathway

Cortex (most areas) -> striatum

Question 8

What makes up the striatum?

Answer 8

Putamen (sensory and motor areas)

Caudate nucleus (association areas and frontal eye field)

Question 9

What neurones receive most of the cortical input to BG

Answer 9

Striatal medium spiny neurones

• distributed into modules called strisomes, surrounded by matrix
• inhibitoryGABAergic

Question 10

Direct and indirect pathways

Answer 10

Direct: striatum to SNr/GPi

Indirect: striatum to GPe then STN (excitatory) then SNr/GPi

Question 11

Describe the hyper direct pathway

Answer 11

Direct excitatory pathway between cortex and STN

Question 12

Function of direct/ indirect pathways

Answer 12

Opposing functions:

Direct: activation reduces basal ganglia output

Indirect: activation increases BG output

Question 13

How does the direct pathway drive movement?

Answer 13

1. Cortex excites MSNs in striatum
2. These are GABAergic and inhibitory and so send inhibitory signals to GP and SN
3. GP and SN are tonically active and so their disinhibition reduces inhibitory BG output to thalamus
4. Thalamus increases activity to cortex

Question 14

Describe the indirect motor pathway (inhibits movement)

Answer 14

1. Cortex stimulates striatum
2. Increased inhibitory output to tonically active GPe
3. Therefore reduced inhibitory output to STN
4. Increased excitatory output from STN to GPi ane SN
5. Increased inhibitory output from there to thalamus
6. Less active thalamus