Cerebellar cortex (grey)

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Cerebellum

General

• A thin layer covering the central core of white matter

• Has 3 layers

Molecular layer (most superficial, just below pia)

• Mainly a synaptic layer which is sparsely populated Contains
• Dendrites of Purkinje cells
• Axon of granule cells
• Interneurons
• Stellate cells:
• Inhibitory interneurons
• Situated in the superficial part of the molecular layer
• Dendrites: synapse with parallel fibres of granule cells
• Axons: synapse with dendrites of Purkinje cells
• Basket cells: Situated in the deeper layer
• Inhibitory interneurons
• Dendrites: synapse with parallel fibres of granule cells
• Axons: branch and form networks (or baskets) around the cell bodies of Purkinje cells
• Synapse with Purkinje cells at the junction of the cell body and axon (preaxon).

Purkinje cell layer

General

• Contains a single layer of Purkinje cells.

• One cell type

Purkinje cells

• Inhibitory neurons

• Flask-shaped cell bodies

• Evenly spaced

• Dendrite
• Arises from the “neck” of the “flask”
• Passes “upwards” into the molecular layer
• Divides into a “tree”. All the branches lie in one plane!
• This plane is transverse to the long axis of the folium
• Hence, Dendritic tree all lie parallel to one another

• Axon:
• Passes “downwards” through the granular layer to enter the white matter.
• Constitute the only efferent (output) of the cerebellar cortex.
• End predominantly by synapsing with neurons in cerebellar nuclei.
• They are inhibitory to these neurons.

Granular layer (lies on white matter)

General

• Contains densely packed neurons that send axonal projections into the molecular layer

• Has 3 different cell types

Granule cells (most)

• (Stimulatory)

• Very small, numerous and spherical neurons

• Occupy most of the granular layer

• The spaces not occupied by them are called cerebellar islands.
• These islands are occupied by special synaptic structures called glomeruli

• Dendrite
• Each cell gives off 3-5 short dendrites
• End in claw like endings
• Enter the glomeruli
• Synapse with terminals of mossy fibers

• Axon
• Enters the molecular layer and divides into Parallel fibers
• Formed from two right angled subdivisions of axons (forming a T-junction).
• Since there is numerous granule cells → parallel fibres are also numerous → parallel fibres fill the molecular layer.
• Synapses with
• Purkinje cells
• The parallel fibres run at right angles to the planes of the dendritic trees of Purkinje cells.
• Golgi cells
• Basket cells
• Stellate cells

 

• Pathology
• Group 3 Medulloblastoma
• SHH medulloblastoma (LRL)
• Dysplastic cerebellar gangliocytoma

Golgi cells (least)

• Inhibitory interneurons

• There is no overlap between each territory Golgi cells
• Territory of each Golgi cell corresponds to that of about 10 Purkinje cells.

Unipolar brush cells (UBC)

• Excitatory glutamatergic interneuron

• Found in the granular layer
• Also found in granule cell domain of cochlear nuclei

• UBC has a round or oval cell body with usually a single short dendrite that ends in a brush-like tuft of short dendrioles (dendrites unique to UBCs).

• Dendritic brush and the large endings of the axonal branches are involved in the formation of cerebellar glomeruli

• Function
• Amplify inputs from the vestibular ganglia and nuclei by spreading and prolonging excitation within the granular layer

• Pathology
• Group 4 Medulloblastoma (URL)

Transient: External granule cell layer

• An embryonic cerebellar layer,

• Is present during the prenatal and early postnatal periods but is completely gone by the first year of life.

• Its cells are thought to be the cell of origin of medulloblastomas.