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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- 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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- 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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- 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:
- Superior Cerebellar Peduncle: Efferent pathway, projecting to upper motor neurons in motor cortex and superior colliculus.
- Middle Cerebellar Peduncle: Afferent pathway with over 20 million axons from contralateral pontine nuclei.
- 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