Brain
Cerebellum
Precision coordinator of movement and learning
Overview
Although the cerebellum accounts for only 10% of brain volume, it contains over 50% of all neurons. Situated at the back and bottom of the brain, it fine-tunes motor movements, coordinates balance and posture, and plays a growing recognised role in cognitive functions like timing, language processing, and emotional regulation.
Function
- Fine-tunes and coordinates voluntary movements
- Maintains posture and balance
- Procedural motor learning (e.g., riding a bike)
- Predicts sensory consequences of movement
- Cognitive timing and rhythm processing
Key Facts
- The cerebellum has ~69 billion neurons—more than the rest of the brain combined
- It operates subconsciously—you cannot will it to act directly
- Rugby players show enlarged cerebellum hand representations
- Cerebellar damage causes ataxia: uncoordinated, jerky movements
Key Substructures
- Vermis: midline structure coordinating gait, trunk posture, and eye movements
- Cerebellar hemispheres: coordinate ipsilateral limb movements and complex motor sequences
- Cerebellar cortex: three-layered sheet containing the distinctive Purkinje cell layer
- Deep cerebellar nuclei (dentate, interpositus, fastigial): sole output relays of the cerebellum
- Flocculonodular lobe (vestibulocerebellum): balance, vestibular control, and smooth eye tracking
Clinical Notes
- Damage causes ataxia: wide-based gait, incoordination, and loss of balance
- Intention tremor: shaking that worsens as a limb approaches a target
- Dysmetria: overshooting or undershooting during reaching movements
- Dysarthria: slurred, scanning speech from impaired motor coordination
- Alcohol intoxication acutely mimics cerebellar damage (ataxia, dysarthria)