Basal Ganglia and Cerebellum

Question 1

What are the basal ganglia and cerebellum involved in?

Answer 1

involved in control of movement

do not have direct, descending projections to spinal cord

Question 2

What do basal ganglia and cerebellum modify?

Answer 2

modify motor performance by means of projections – feed back to motor cortex to influence its output

Question 3

What are the basal ganglia and cerebellum components of?

Answer 3

components of circuits (loops) of neurons

activity is being constantly modified, depending on prevailing conditions and motor requirements

Question 4

What do the basal ganglia and cerebellum both receive copies of?

Answer 4

both receive ‘copy’ of motor command that is going to motor neurons

this information is processed before returning to cortical origin

Question 5

What does the cerebellum play a fundamental role in?

Answer 5

regulating motor output of cerebral cortex – via projection from dentate nucleus to thalamus, and back to cerebral cortex

Question 6

What does the cerebral cortex do?

Answer 6

gives rise to corticospinal tract, which results in movement of opposite side of body

Question 7

How does a copy of the information from the cerebral cortex reach the cerebellum?

Answer 7

by way of corticopontine fibres, pontine nuclei, and middle cerebellar peduncle

Question 8

How is movement detected?

Answer 8

by proprioceptors

information (result of original command) is transmitted to cerebellum via spinocerebellar tract and inferior cerebellar peduncle

Question 9

What does the cerebellar cortex compare? What happens to the result of the comparison?

Answer 9

compares command to actual performance (feedback)

result of comparison leaves cerebellum via dentate nucleus and superior cerebellar peduncle

Question 10

What is the major destination of the projection that leaves cerebellum (result of comparison of command to actual performance)?

Answer 10

thalamus

• VA/VL – mainly VL
• back to cerebral cortex

Question 11

What is the minor destination of the projection that leaves cerebellum (result of comparison of command to actual performance)?

Answer 11

red nucleus

Question 12

What does the minor projection to the red nucleus do?

Answer 12

• does not influence cerebral cortex

- modifies motor function by minor projection to cord and to reticular formation

Question 13

What are the main structures of the basal ganglia? (4)

Answer 13

• striatum or caudate/putamen (C/P)
• globus pallidus – external and internal division (GPe and GPi)
• substantia nigra (SN)
• subthalamic nucleus (ST)

Question 14

What does the cortex do?

Answer 14

• gives rise to motor output – corticospinal and corticobulbar fibres
• projects to C/P – glutamate

Question 15

Where is the output of basal ganglia from?

Answer 15

GPi

Question 16

What is the output of the basal ganglia?

Answer 16

inhibitor (GABA) to thalamus (VL and VA – mainly VA)

Question 17

What is the projection from thalamus back to cortex?

Answer 17

excitatory

uses glutamate

Question 18

What are the 2 pathways between C/P and GPi?

Answer 18

direct pathway – on top

indirect pathway – on bottom

Question 19

What is the direct pathway between C/P and GPi? What does it do?

Answer 19

• stimulates movement

- single inhibitory neuron – GABA

Question 20

What is the indirect pathway between C/P and GPi? What does it do?

Answer 20

• reduces movement

- chain of 2 inhibitory neurons – impinging on excitatory neuron in ST

Question 21

What do the pathways between C/P and GPi of the basal ganglia act on?

Answer 21

pathways act upon output cell in GPi

output cell (which inhibits thalamus) is under influence of 2 opposing influences

Question 22

When would the thalamus be inhibited?

Answer 22

if activity of output cell is decreased by either:

• decreasing the drive from ST
• increasing inhibitory drive from direct pathway

Question 23

*** The result of thalamus disinhibition would be…

Answer 23

increased activity to cortex

• increased cortical output
• more movement

Question 24

What projects from the substantia nigra (SN)?

Answer 24

dopaminergic projection from SN

Question 25

What does dopamine do to the pathways between C/P and GPi in the basal ganglia?

Answer 25

• dopamine stimulates direct pathway (D1 receptors)

- dopamine inhibits indirect pathway (D2 receptors)

Question 26

What happens if there is a loss of dopamine?

Answer 26

loss of movement – ie. Parkinson’s Disease

Question 27

What does excessive movement cause?

Answer 27

• degeneration of indirect pathway
• ballismus – lesion on ST

ie. occurs in Huntington’s Disease

Question 28

What is ballismus?

Answer 28

severe movement disorder characterized by spontaneous involuntary movements, weakness, and incoordination of movements of the proximal extremities