Cerebellum Flashcards

1
Q

The subcortical motor controllers

A
  • basal ganglia and cerebellum (regulate planning and execution of voluntary movement)
  • both receive cotical inputs a both project via thalamus to motor cortex
  • both needed for somooth movement and posture
  • lesions - positive and negative motor symptoms
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2
Q

The cerebellum

A
  • 10% of brain volume but has more than half of the brain’s neurons
  • CBM has expanded during our evolution - suggests it has done a good job
  • 40x more input axons than outputs
  • most outputs project to motor areas
  • but NOT to the spinal cord (doesnt wire to the alphaMN in the spinal cord at all, goes to descending nuclei)
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3
Q

Cerebellar lesions

A
  • give great difficulty in performing tasks
  • affect ipsilateral side
  • dont lead to weakness - just clumsiness
  • hypotonia (low muscle tone and uncoordinated contraction)
  • postural ataxia (cant keep stable posture)
  • intention (action) tremor - overshhot, oscillation of voluntary movement
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4
Q

What is the function of the CBM?

A
  • improves performance in the future - motor learning

- rapid on-line refinement of a rapid movement

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5
Q

CBM as a feedback comparator

A
  • Cortex sends out a set of commands - causes muscles to contract and sensory receptors are activated
  • if you make a clumsy movement, the sensory receptors will send a signal back to the brain via CBM giving feedback
  • CBM sends a signal to cerebral cortex next time to improve the movements
  • way too slow for online control where you need to be able to change movements instantly - even if you have never dealt with it before
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6
Q

Feed-forward control

A
  • There is time for this to happen in ballistic movements
  • as the cerebral cortex sends a signal for movement, collateral fibres get sent to the cerebellum
  • CBM has a blueprint of the body so it can send feedback, telling the motor cortex how a movement will go before it even happens
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7
Q

What are the three anatomical/functional domains?

A
  • spino-cerebellum (central zone) = modulates descending motor systems in brainstem via reticular formation and vestibular nuclei
  • Vestibulo-cerebellum = regulates balance and eye movements via vestibular nuclei
  • cerebro-cerebellum = high level planning of movement, regulates cortical motor programs via thalamus
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8
Q

Cerebro-cerebellar pathways

A
  • commands come down from motor area
  • get sent to spinal cord, but a branch sends a copy to cerebellum
  • Signal goes down to the CBM through the pontine nucleus
  • feedback then comes out from the deep cerebellar nuclei to the brain stem, via the thalamus and back up to the cortex
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9
Q

Somatotopic map

A
  • we have a very crude homunculus of the body that we can somatotopically map onto the cerebellum
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10
Q

Cellular structure

A
  • highly regular structure
  • purkinje cells - huge neurons
  • purkinje cells (inhibitory) project to the deep cerebellar nuclei (excitatory) - project out via thalamic relays to the cortex
  • granule cells - very numerous
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11
Q

Purkinje neurons

A
  • cell body is very big
  • tree-like growth of dendrites - very narrow tree (like a plate)
  • purkinjes project down to deep nuclei
  • lined up in layers
  • there are two influences, parallel fibres and climbing fibres
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12
Q

Climbing fibres

A
  • climbing fibres come from ccx and go via inferior olive
  • each purkinje cell has one climbing fibre that wraps around it
  • each climbing fibre wraps around about 10 purkinjes
  • if climbing fibre fires an AP, so does the purkinje cell
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13
Q

Parallel fibres

A
  • Mossy fibres from the pons/brainstem nuclei synapse onto the granule cells - these produce the parallel fibres
    = these go through the plates of dendrites of the purkinje cells at a 90 degree angle
  • each fibre come from a different granule neurone
  • each one forms a synapse as it goes through
  • there are about 1 million parallel fibres per purkinje, and each parallel fibre will synapse onto many purkinje cells
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14
Q

Cerebellar learning

A
  • as the motor cortex sends out a set of commands to make a movement, the commands are copied via mossy fibres to the granule cells
  • carry the movements out to the purkinje dendrites
  • the climbing fibre receives input from the rewards system
  • when you make a good movement, the reward system fires
  • the climbing fibres carry APs and so the purkinje cells that were activated at the time of the good movement, will get a stimulus
  • all the synapses active at the time will get reinforced > synaptic strengthening
  • the ones fired when you do a clumsy movement will get weaker and eventually die away
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15
Q

Summary

A
  • motor learning - when the movement is repeated, CBM gives corrective feedback
  • feed-forward comparator - CBM refines a rapid movement on-line
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