Physiology chapters
Cerebellum
What each functional part of the cerebellum does, how its circuits compare intended and actual movement, its role in posture, balance and motor learning, and the signs of cerebellar disease.
- The cerebellum compares intended movement with actual movement and corrects errors; it controls the same side of the body.
- Three divisions: vestibulocerebellum (balance, eye movements), spinocerebellum (posture and ongoing movement) and cerebrocerebellum (planning and timing of skilled movement).
- Damage causes ataxia, intention tremor, dysmetria, dysdiadochokinesia, nystagmus and hypotonia.
On this page
Overview
The cerebellum does not start movement and its damage does not cause paralysis. Instead, it makes movement smooth, accurate and well timed.
It works as a comparator: it receives a copy of the motor command from the cortex and signals from muscles and joints about what actually happened, then sends corrections.
For the structures, peduncles and nuclei, see the anatomy page on the cerebellum.
Functional divisions
| Division | Parts | Main input | Output through | Role |
|---|---|---|---|---|
| Vestibulocerebellum | Flocculonodular lobe | Vestibular nuclei | Vestibular nuclei | Balance and eye movements |
| Spinocerebellum | Vermis and intermediate zones | Spinal cord (spinocerebellar tracts), copy of cortical commands | Fastigial and interposed nuclei | Posture, muscle tone and correcting movements as they happen |
| Cerebrocerebellum | Lateral hemispheres | Cerebral cortex via the pontine nuclei | Dentate nucleus → thalamus → cortex | Planning, sequencing and timing of skilled movement |
The vermis (midline) controls the trunk and posture; the lateral hemispheres control skilled limb movements.
The cerebellar circuit
Inputs
- Mossy fibres: from the spinal cord, pons, vestibular nuclei and other sources. They excite granule cells, whose parallel fibres excite many Purkinje cells.
- Climbing fibres: all from the inferior olive. Each wraps around one Purkinje cell and excites it very strongly.
Output
Purkinje cells are the only output of the cerebellar cortex. They are inhibitory (GABA) and project to the deep cerebellar nuclei (and the vestibular nuclei).
The deep nuclei are excited by the incoming fibres and inhibited by Purkinje cells. Their balance sets the final output to the brainstem and thalamus.
The deep nuclei send the cerebellum's output; the Purkinje cells shape it by inhibition.
Why it controls the same side
Output from the dentate nucleus crosses to the opposite thalamus and motor cortex. The corticospinal tract then crosses back in the medulla. Two crossings bring control to the same side of the body.
Functions
Balance and eye movement
The vestibulocerebellum uses signals from the inner ear to keep balance and to keep the eyes steady on a target while the head moves.
Posture and correcting ongoing movement
The spinocerebellum compares the intended movement (copy of the cortical command) with feedback from muscle spindles, tendon organs and joints. If the limb is off course, it sends corrections through the red nucleus and the motor cortex.
It also provides the damping function, stopping a movement at the right point without overshooting.
Planning and timing
The cerebrocerebellum plans the next movement in a sequence while the current one is happening. It also helps judge the timing of events and the speed of moving objects.
Motor learning
When a movement is performed poorly, climbing fibres signal the error. Repeated error signals change the strength of synapses between parallel fibres and Purkinje cells (long-term depression). Over time, the movement becomes accurate and automatic.
Climbing fibres from the inferior olive are the error signal for motor learning.
Signs of cerebellar disease
DANISH: Dysdiadochokinesia, Ataxia, Nystagmus, Intention tremor, Slurred (scanning) speech, Hypotonia.
| Sign | What it means |
|---|---|
| Ataxia | Unsteady, poorly coordinated movement; wide-based, staggering gait |
| Dysmetria | Overshooting or undershooting a target ("past pointing" in the finger-nose test) |
| Intention tremor | Tremor that increases as the hand approaches a target |
| Dysdiadochokinesia | Inability to perform rapid alternating movements |
| Rebound phenomenon | The limb flies back when sudden resistance is removed (loss of damping) |
| Nystagmus | Jerky eye movements, often towards the side of the lesion |
| Scanning speech | Slow, slurred speech broken into syllables |
| Hypotonia | Reduced muscle tone; pendular knee jerk |
Cerebellar signs appear on the same side as the lesion, unlike cortical lesions.
Patterns of damage
- Vermis / midline (alcohol, midline tumours in children): truncal ataxia, wide-based gait, difficulty sitting or standing still; limb tests may be nearly normal.
- Hemisphere: limb ataxia, intention tremor and dysmetria on the same side.
- Flocculonodular lobe: loss of balance and nystagmus.
Clinical relevance
Alcohol
How it happens: long-term alcohol misuse damages the anterior vermis.
What you see: a wide-based, unsteady gait affecting the legs more than the arms.
Posterior fossa tumours
How it happens: medulloblastoma in children (often midline) or metastases in adults.
What you see: cerebellar signs and raised pressure if the fourth ventricle is blocked.
Expect: the three functional divisions and their roles, the Purkinje cell as the only (inhibitory) output, climbing vs mossy fibres, the error signal in motor learning, same-side control, and the cerebellar signs with their meaning.
Quick revision
- Cerebellum compares intended and actual movement; same-side control.
- Vestibulocerebellum: balance and eyes. Spinocerebellum: posture and correction. Cerebrocerebellum: planning and timing.
- Purkinje cells: only cortical output; inhibitory.
- Climbing fibres (inferior olive): error signal for motor learning.
- Signs: DANISH, dysmetria, rebound.
- Vermis lesion: truncal ataxia. Hemisphere lesion: limb ataxia.
Written by The House Job from standard physiology references (Guyton and Hall Textbook of Medical Physiology; BRS Physiology).
FAQ
What is the main function of the cerebellum?
It coordinates movement by comparing intended movements with actual movements and correcting errors.
What is the only output of the cerebellar cortex?
Purkinje cells, which inhibit the deep cerebellar nuclei.
What is an intention tremor?
A tremor that becomes worse as the hand approaches a target, typical of cerebellar disease.
Which fibres signal errors for motor learning?
Climbing fibres from the inferior olive.