Anatomy chapters
Cerebellum
The lobes and functional parts of the cerebellum, its peduncles, deep nuclei and cortex, and how midline and hemisphere lesions show up as ataxia, intention tremor and nystagmus.
- The cerebellum coordinates movement, balance and muscle tone; it controls the same side of the body.
- It connects to the brainstem by three peduncles: superior (mainly output), middle (input from pons) and inferior (input from cord and medulla).
- Midline (vermis) lesions cause truncal ataxia; hemisphere lesions cause limb ataxia on the same side.
On this page
Overview
The cerebellum lies in the posterior cranial fossa, behind the pons and medulla, under the tentorium cerebelli.
It does not start movements. It compares what the brain intends with what the body is doing, and corrects movement so it is smooth, accurate and balanced.
It controls the same side of the body.
External features
- A narrow midline vermis and two large hemispheres.
- The surface has thin parallel folds called folia.
- The tonsils are rounded parts of the hemispheres on the underside, just above the foramen magnum.
Lobes and functional parts
Two deep fissures divide the cerebellum into three lobes.
| Lobe | Functional name | Main input | Role |
|---|---|---|---|
| Flocculonodular | Archicerebellum (vestibulocerebellum) | Vestibular nuclei | Balance and eye movements |
| Anterior | Paleocerebellum (spinocerebellum) | Spinal cord (spinocerebellar tracts) | Muscle tone and posture of the trunk and limbs |
| Posterior (largest) | Neocerebellum (cerebrocerebellum) | Cerebral cortex via the pons | Planning and fine coordination of skilled limb movements |
The flocculonodular lobe (vestibulocerebellum) is concerned with balance and eye movements.
Peduncles
Three pairs of peduncles join the cerebellum to the brainstem.
| Peduncle | Connects to | Main fibres |
|---|---|---|
| Superior | Midbrain | Output from the dentate and other deep nuclei to the red nucleus and thalamus; also the anterior spinocerebellar tract (input) |
| Middle (largest) | Pons | Input from the pontine nuclei (cortico-ponto-cerebellar pathway) |
| Inferior | Medulla | Input from the spinal cord (posterior spinocerebellar tract), inferior olive and vestibular nuclei; some output to vestibular nuclei |
The superior peduncle is mainly output; the middle and inferior are mainly input.
Internal structure
Cerebellar cortex
Three layers, from outside in:
- Molecular layer: mainly fibres and a few neurons.
- Purkinje cell layer: a single row of large Purkinje cells.
- Granular layer: many small granule cells.
Inputs:
- Climbing fibres: from the inferior olive, one to each Purkinje cell.
- Mossy fibres: from all other sources (spinal cord, pons, vestibular nuclei), ending on granule cells.
Purkinje cells are the only output of the cerebellar cortex, and they are inhibitory (they use GABA). They project to the deep nuclei.
Deep cerebellar nuclei
From lateral to medial: dentate, emboliform, globose, fastigial.
"Don't Eat Greasy Food": dentate, emboliform, globose, fastigial (lateral to medial).
- The dentate nucleus (largest) receives from the hemisphere and sends output through the superior peduncle to the opposite red nucleus and thalamus, and from there to the motor cortex.
- The fastigial nucleus connects with the vestibular nuclei and reticular formation for balance.
Why the cerebellum controls the same side
Output from the dentate nucleus crosses in the superior peduncle to the opposite thalamus and motor cortex. The motor cortex then sends the corticospinal tract, which crosses again in the medulla. Two crossings bring control back to the same side.
Signs of cerebellar disease
DANISH: Dysdiadochokinesia, Ataxia, Nystagmus, Intention tremor, Slurred (scanning) speech, Hypotonia.
- Dysdiadochokinesia: cannot make quick alternating movements (such as turning the hand over and back).
- Ataxia: clumsy, unsteady walking and limb movements; the gait is wide-based.
- Nystagmus: jerky eye movements, often worse looking towards the side of the lesion.
- Intention tremor: tremor that gets worse as the hand nears a target; with past pointing (dysmetria) in the finger-nose test.
- Scanning (staccato) speech: slow, slurred, with words broken into syllables.
- Hypotonia: reduced muscle tone; pendular reflexes.
Signs appear on the same side as a cerebellar hemisphere lesion.
Intention tremor (cerebellar) gets worse on movement. A resting tremor that improves on movement is typical of Parkinson's disease.
Midline vs hemisphere lesions
| Lesion | Signs |
|---|---|
| Vermis / midline (for example medulloblastoma in a child, chronic alcohol) | Truncal ataxia: wide-based, unsteady gait; cannot sit or stand steadily; limb coordination can be near normal |
| Hemisphere | Limb ataxia on the same side: intention tremor, past pointing, dysdiadochokinesia |
Chronic alcohol misuse damages the anterior vermis, giving a wide-based gait that affects the legs more than the arms.
Clinical relevance
Tonsillar herniation (coning)
How it happens: raised pressure in the posterior fossa pushes the cerebellar tonsils down through the foramen magnum.
What you see: compression of the medulla and its breathing centres; can cause sudden death. This is why lumbar puncture is avoided when pressure is high from a mass.
Posterior fossa tumours
How it happens: medulloblastoma (children, midline) or metastases and haemangioblastoma (adults).
What you see: cerebellar signs and, if the fourth ventricle is blocked, hydrocephalus with headache and vomiting.
Cerebellar stroke
How it happens: blockage of a cerebellar artery (PICA, AICA, superior cerebellar).
What you see: sudden vertigo, vomiting, unsteadiness and same-side limb ataxia; swelling can block the fourth ventricle.
Common questions: same-side control, the three peduncles and which is output, the functional parts, the deep nuclei order, Purkinje cells as the only (inhibitory) output, the DANISH signs, and midline vs hemisphere lesions.
Quick revision
- Cerebellum controls the same side.
- Flocculonodular: balance. Anterior: tone and posture. Posterior: fine limb coordination.
- Superior peduncle: output. Middle: from the pons (largest). Inferior: from cord and olive.
- Purkinje cells: only cortical output; inhibitory.
- Deep nuclei: dentate, emboliform, globose, fastigial.
- DANISH signs; intention tremor worse near the target.
- Vermis lesion: truncal ataxia. Hemisphere lesion: same-side limb ataxia.
Written by The House Job from standard neuroanatomy references (Snell's Clinical Neuroanatomy).
FAQ
Does the cerebellum control the same or the opposite side?
The same side of the body, because its output crosses twice.
Which cerebellar peduncle carries the main output?
The superior cerebellar peduncle.
What are the signs of cerebellar disease?
Dysdiadochokinesia, ataxia, nystagmus, intention tremor, scanning speech and hypotonia (DANISH).
What is the only output of the cerebellar cortex?
The Purkinje cells, which inhibit the deep cerebellar nuclei.