The Cerebellum Flashcards

1
Q

Which 2 subcortical motor controllers are required for smooth movement and posture?

A

Basal ganglia and cerebellum

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2
Q

The cerebellum contributes 10% to total brain volume. What proportion of all neurons in the brain does it contain?

A

More than 50%

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3
Q

Name the classic triad of symptoms for a cerebellar lesion.

A
  1. Hypotonia - low muscle tone, uncoordinated muscle contraction
  2. Postural ataxia - can’t keep stable posture, especially with eyes closed
  3. Intention (action) tremor - overshoot, oscillation of voluntary movements
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4
Q

What are the 2 main functions of the cerebellum?

A
  1. Improves future performance - motor learning
  2. Rapid on-line refinement of a “ballistic” (rapid, explosive) movement
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5
Q

How does the cerebellum act as a “feed-forward comparator”?

A
  • Cerebellum receives collateral projections from the motor cortex
  • It has an internal model of the body for on-line control
  • Cerebellar loop - receives from cortex and feeds “forward” to cortex before motor activity is executed
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6
Q

Describe the basic characteristics of the 3 anatomical/functional domains of the cerebellum.

A
  • Spino-cerebellum - modulates descending motor systems in brainstem (via reticular formation)
  • Vestibulo-cerebellum - regulates balance and eye movements (via vestibular nuclei)
  • Cerebro-cerebellum - high level planning of movement; regulates cortical motor programs (via thalamus to cortex)
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7
Q

Describe the characteristics of the Purkinje and granule cells of the cerebellum.

A

Purkinje cells -

  • Huge output neurons
  • GABAergic, inhibitory
  • Project to deep cerebellar nuclei, thalamus (and hence cortex), reticular formation, vestibular nucleus
  • Deep cerebellar nuclei contain excitatory glutamatergic neurons

Granule cells:

  • Very numerous, approx 1011
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8
Q

Name the 2 excitatory inputs to the cerebellar Purkinje fibres and explain the interaction between these cells.

A

Climbing fibres:

  • Cerebral cortex > inferior olive > cerebellum
  • Approx 10 Purkinje fibres to 1 climbing fibre
  • 1 climbing fibre synapses many times with each Purkinje cell - huge spatial summation, meaning Purkinje cell invariably excited

Parallel fibres:

  • Mossy fibres from pons/brainstem nuclei > parallel fibres from granule cells
  • 1 million parallel fibres per Purkinje cell, many Purkinje cells per parallel fibre
  • Each parallel fibre forms very few synapses with the Purkinje cell, but many parallel fibres synapse with the same cell
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9
Q

What happens to the cerebellar parallel fibres and Purkinje cells when a motor command is successful?

A
  • Synapses between parallel fibres and Purkinje cells are strengthened
  • Repetition of successful movement causes long-term synaptic potentiation
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10
Q

Outline how the cerebellum contributes to motor learning and acts as a feed-forward comparator.

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