Basal Ganglia and Cerebellum Flashcards
What are the basal ganglia and cerebellum involved in?
involved in control of movement
do not have direct, descending projections to spinal cord
What do basal ganglia and cerebellum modify?
modify motor performance by means of projections – feed back to motor cortex to influence its output
What are the basal ganglia and cerebellum components of?
components of circuits (loops) of neurons
activity is being constantly modified, depending on prevailing conditions and motor requirements
What do the basal ganglia and cerebellum both receive copies of?
both receive ‘copy’ of motor command that is going to motor neurons
this information is processed before returning to cortical origin
What does the cerebellum play a fundamental role in?
regulating motor output of cerebral cortex – via projection from dentate nucleus to thalamus, and back to cerebral cortex
What does the cerebral cortex do?
gives rise to corticospinal tract, which results in movement of opposite side of body
How does a copy of the information from the cerebral cortex reach the cerebellum?
by way of corticopontine fibres, pontine nuclei, and middle cerebellar peduncle
How is movement detected?
by proprioceptors
information (result of original command) is transmitted to cerebellum via spinocerebellar tract and inferior cerebellar peduncle
What does the cerebellar cortex compare? What happens to the result of the comparison?
compares command to actual performance (feedback)
result of comparison leaves cerebellum via dentate nucleus and superior cerebellar peduncle
What is the major destination of the projection that leaves cerebellum (result of comparison of command to actual performance)?
thalamus
- VA/VL – mainly VL
- back to cerebral cortex
What is the minor destination of the projection that leaves cerebellum (result of comparison of command to actual performance)?
red nucleus
What does the minor projection to the red nucleus do?
- does not influence cerebral cortex
- modifies motor function by minor projection to cord and to reticular formation
What are the main structures of the basal ganglia? (4)
- striatum or caudate/putamen (C/P)
- globus pallidus – external and internal division (GPe and GPi)
- substantia nigra (SN)
- subthalamic nucleus (ST)
What does the cortex do?
- gives rise to motor output – corticospinal and corticobulbar fibres
- projects to C/P – glutamate
Where is the output of basal ganglia from?
GPi
What is the output of the basal ganglia?
inhibitor (GABA) to thalamus (VL and VA – mainly VA)
What is the projection from thalamus back to cortex?
excitatory
uses glutamate
What are the 2 pathways between C/P and GPi?
direct pathway – on top
indirect pathway – on bottom
What is the direct pathway between C/P and GPi? What does it do?
- stimulates movement
- single inhibitory neuron – GABA
What is the indirect pathway between C/P and GPi? What does it do?
- reduces movement
- chain of 2 inhibitory neurons – impinging on excitatory neuron in ST
What do the pathways between C/P and GPi of the basal ganglia act on?
pathways act upon output cell in GPi
output cell (which inhibits thalamus) is under influence of 2 opposing influences
When would the thalamus be inhibited?
if activity of output cell is decreased by either:
- decreasing the drive from ST
- increasing inhibitory drive from direct pathway
*** The result of thalamus disinhibition would be…
increased activity to cortex
- increased cortical output
- more movement
What projects from the substantia nigra (SN)?
dopaminergic projection from SN
What does dopamine do to the pathways between C/P and GPi in the basal ganglia?
- dopamine stimulates direct pathway (D1 receptors)
- dopamine inhibits indirect pathway (D2 receptors)
What happens if there is a loss of dopamine?
loss of movement – ie. Parkinson’s Disease
What does excessive movement cause?
- degeneration of indirect pathway
- ballismus – lesion on ST
ie. occurs in Huntington’s Disease
What is ballismus?
severe movement disorder characterized by spontaneous involuntary movements, weakness, and incoordination of movements of the proximal extremities
