Cerebellum cortex has 3 layers

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Yes, the cerebellar cortex has exactly 3 layers. Here is a detailed breakdown from multiple authoritative neuroscience and physiology textbooks:

Cerebellar cortex layers cross-section showing molecular, Purkinje cell, and granular layers with all cell types and fiber connections

Fig. 3.36 - Costanzo Physiology 7th Ed. Cross-section of the cerebellar cortex.

The Three Layers of the Cerebellar Cortex

1. Granular Layer (Innermost - "Input Layer")

Contains granule cells (~100 billion - the most numerous neurons in the brain), Golgi II cells, and glomeruli
Mossy fibers (from spinocerebellar and pontocerebellar tracts) terminate here, synapsing on granule and Golgi type II cell dendrites within the glomeruli
Golgi cells provide inhibitory feedback onto granule cells
The granular layer is functionally the input layer of the cerebellar cortex
Also contains smaller populations of cells of Lugaro, unipolar brush cells, and chandelier cells

2. Purkinje Cell Layer (Middle - "Output Layer")

Consists of a single sheet of Purkinje cell bodies (each 50-80 µm in diameter)
Purkinje cells are among the largest neurons in the CNS, with extensive dendritic arbors extending up into the molecular layer
Their axons carry the sole output of the cerebellar cortex, projecting to:
- Deep cerebellar nuclei (especially the dentate nucleus)
- Vestibular nuclei in the brain stem
Output is always inhibitory (via GABA)
Each Purkinje cell dendrite can receive input from up to 250,000 parallel fibers
Each Purkinje cell receives input from only one climbing fiber, which produces powerful "complex spikes"

3. Molecular Layer (Outermost)

Contains outer stellate cells and basket cells - both inhibitory interneurons that inhibit Purkinje cells
Contains the fan-like dendrites of Purkinje cells and dendrites of Golgi II cells
Contains parallel fibers - the T-shaped bifurcating axons of granule cells that run parallel to the long axis of the cerebellar folia and synapse perpendicularly across the Purkinje cell dendritic trees

The 5 Cell Types of the Cerebellar Cortex (Summary)

Cell	Layer	Function
Granule cells	Granular	Excitatory interneurons; relay mossy fiber input via parallel fibers
Golgi II cells	Granular (body) / Molecular (dendrites)	Inhibitory feedback onto granule cells
Purkinje cells	Purkinje cell layer	Sole output of cortex; inhibitory (GABA)
Basket cells	Molecular	Inhibit Purkinje cells
Stellate cells	Molecular (outer)	Inhibit Purkinje cells

Two Afferent Input Systems

Fiber	Origin	Terminates On	Effect on Purkinje cell
Mossy fibers	Vestibular, spinal, pontine nuclei	Granule cells (via glomeruli)	Indirect via parallel fibers → simple spikes
Climbing fibers	Inferior olivary nucleus (medulla)	Purkinje cell proximal dendrites directly	Direct, powerful → complex spikes (1 climbing fiber per Purkinje cell)

Both systems also send collateral branches directly to the deep cerebellar nuclei, bypassing the cortex.

Sources: Costanzo Physiology 7th Ed., p. 114 | Kandel Principles of Neural Science 6th Ed. | Ganong's Review of Medical Physiology 26th Ed. | Localization in Clinical Neurology 8th Ed.

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