Human Anatomy
Cerebellum
Cerebellum anatomy for MBBS: peduncles, cortical layers, deep nuclei, functional divisions and cerebellar signs, mapped to NMC codes AN60.1 to AN60.3.
MedNext Academy | 3 min read
Cerebellum
Cerebellum anatomy for MBBS: peduncles, cortical layers, deep nuclei, functional divisions and cerebellar signs, mapped to NMC codes AN60.1 to AN60.3.
This chapter describes the gross structure, cortical histology, deep nuclei and functional divisions of the cerebellum. It explains why cerebellar lesions cause ipsilateral incoordination and the classic clinical signs of cerebellar disease.
High-yield: Cerebellum
- The cerebellum has two hemispheres joined by a midline vermis and lies in the posterior cranial fossa.
- It is connected to the brainstem by three peduncles: superior to the midbrain, middle to the pons and inferior to the medulla.
- The cerebellum controls coordination, balance and muscle tone but does not initiate movement.
- Its cortex has three layers, an outer molecular layer, a middle Purkinje cell layer and an inner granular layer.
- Purkinje cells are the only output neurons of the cerebellar cortex and are inhibitory, using GABA.
- Climbing fibres arise from the inferior olivary nucleus and each wraps around a single Purkinje cell.
- Mossy fibres carry most other input and excite granule cells, whose parallel fibres synapse on many Purkinje cells.
- The four intracerebellar nuclei from medial to lateral are the fastigial, globose, emboliform and dentate.
- The dentate nucleus is the largest and projects through the superior cerebellar peduncle to the opposite thalamus and motor cortex.
- The archicerebellum or flocculonodular lobe governs balance and eye movements through vestibular connections.
- The palaeocerebellum or vermis and paravermis controls posture and muscle tone of the trunk.
- The neocerebellum, the large lateral hemispheres, plans and coordinates skilled limb movements.
- Cerebellar signs are ipsilateral because the output crosses once and the corticospinal tract crosses again, a double crossing.
- Cerebellar dysfunction produces ataxia, intention tremor, dysdiadochokinesia, dysmetria, nystagmus and scanning speech.
- A midline vermis lesion typically causes truncal ataxia and an unsteady gait rather than limb signs.
Cerebellar cortex and output
- **Three cortical layers:** Molecular, Purkinje cell and granular. Purkinje cells are the sole, inhibitory output of the cortex.
- **Two input fibre systems:** Climbing fibres from the inferior olive; mossy fibres from most other sources via granule cells and parallel fibres.
- **Deep nuclei:** Fastigial, globose, emboliform, dentate from medial to lateral. Dentate is largest and projects to the opposite motor cortex.
- **Functional divisions:** Archicerebellum for balance, palaeocerebellum for posture and tone, neocerebellum for skilled limb movement.
NMC competencies in this chapter
- **AN60.1:** External and internal features of the cerebellum
- **AN60.2:** Connections of the cerebellar cortex and the intracerebellar nuclei
- **AN60.3:** Anatomical basis of cerebellar dysfunction
Frequently Asked Questions
Why are cerebellar signs on the same side as the lesion?
Cerebellar output crosses the midline once to reach the opposite motor cortex, and the corticospinal tract then crosses back in the medulla, so the effect returns to the original side. This double crossing makes cerebellar signs ipsilateral.
What are the layers of the cerebellar cortex?
From the surface inward they are the molecular layer, the Purkinje cell layer and the granular layer. The Purkinje cells are the only output neurons and are inhibitory.
Which is the largest deep cerebellar nucleus?
The dentate nucleus. It lies most laterally and sends fibres through the superior cerebellar peduncle to the contralateral thalamus and motor cortex.
What are the classic signs of cerebellar disease?
Ataxia, intention tremor, dysdiadochokinesia, dysmetria, nystagmus, hypotonia and scanning speech. Midline lesions cause truncal ataxia and gait unsteadiness.
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