Modulation of Movement by the Cerebellum

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  • The cerebellum doesn't project directly to spinal cord motoneurons.
  • It regulates upper motoneurons in the motor cortex >> involved in motor learning + if cerebellar deficit = impaired ML
  • Comprises cerebellar cortex and deep cerebellar nuclei.
  • Primary function: detect and correct motor errors, involving sensory-motor integration.

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  1. Cerebrocerebellum:
  • Indirect input from various cerebral cortex areas.
  • Regulates highly skilled movements, e.g., planning and executing complex sequences like speech.

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  1. Spinocerebellum:
  • Direct input from the spinal cord.
  • Lateral part controls distal muscle movement, central part (vermis) regulates proximal muscles and some eye movements.

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  1. Vestibulocerebellum:
  • Oldest part.
  • Receives input from vestibular nuclei in the brainstem.
  • Involved in maintaining posture, balance, and the vestibulo-ocular reflex.

Cerebellar Communication:

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  • Communicates through three cerebellar peduncles:
  1. Superior Cerebellar Peduncle: Efferent pathway, projecting to upper motor neurons in motor cortex and superior colliculus.
  1. Middle Cerebellar Peduncle: Afferent pathway with over 20 million axons from contralateral pontine nuclei.
  1. Inferior Cerebellar Peduncle: Contains multiple afferent and efferent pathways.

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Functional Organization of Inputs:

  • Cerebral cortex provides the largest input, reaching the cerebrocerebellum indirectly via ipsilateral pontine nuclei.
  • Vestibular and somatosensory inputs come through inferior cerebellar peduncle to vestibulocerebellum and spinocerebellum, respectively.

Somatotopic Rep

  • Somatosensory input is organized in topographic maps in the spinocerebellum.
  • Fractured maps represent each body area multiple times by spatially separated cell groups.

Projections from the Cerebellum

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  • Most cerebellar cortex projections go to deep cerebellar nuclei before reaching the target.
  • Thalamus serves as a major relay target to the motor cortex.
  • Four major deep nuclei: dentate, interpositus (2), and fastigial.

Damage to the cerebellum:

  • Causes persistent errors in movement on the same side as the deficit.
  • Alcohol abuse can lead to anterior cerebellar damage and ataxia (difficulty coordinating movement).

Functional Organization of Outputs:

  • Mediolateral organization: fastigial nuclei (medial) mediate axial and proximal muscles, interposed nuclei mediate limbs.

INPUTS:

  • Mossy fibers (from cortex and brainstem >> excitatory to Purkinje)
  • Climbing Fibers: from inferior olive >> exc. synapses onto Purkinje

PURKINJE CELLS = only output cells