Cellular Organization of the Cerebellar Cortex and Functional Organization

 

Cellular Organization of the Cerebellar Cortex and Functional Organization

The cerebellar cortex is a highly organized structure comprising three distinct layers, each with specific types of neurons and functions. These layers work together to ensure proper coordination of movement, balance, and motor learning.

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Layers of the Cerebellar Cortex

• A. Molecular Layer (Outer Layer) :  Contains the dendrites of Purkinje cells and parallel fibers of granule cells,  forming synapses with Purkinje cell dendrites.
• Cell types and functions of cells of molecular layer :
• Stellate Cells: Located superficially; inhibit Purkinje cells through GABAergic synapses.
• Basket Cells: Found deeper in the molecular layer; form inhibitory synapses with Purkinje cells.

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B. Purkinje Layer (Middle Layer) contain Purkinje Cells: Large, flask-shaped neurons arranged in a single layer which receive excitatory input from parallel fibers (granule cells) and climbing fibers (from the inferior olivary nucleus).

Output of this cell is entirely inhibitory (GABAergic) and projects to the deep cerebellar nuclei.

DCN receive excitatory input from mossy fibers and climbing fibers (via collateral branches).

Purkinje cells provide precise inhibitory control over DCN, adjusting the excitatory output based on sensory feedback and motor planning.

 

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• C. Granular Layer (Inner Layer) contains glomeruli (synaptic complexes), where mossy fibers synapse with granule cell dendrites and Golgi cell axons.

 

• Cell Types of granular layer and functions:
• Granule Cells: Small, densely packed neurons; their axons ascend to the molecular layer to form parallel fibers.
• Golgi Cells: Inhibitory interneurons that regulate granule cell activity.

 

2. Functional Organization

Input Pathways:

1. Mossy Fibers:
• Originate from spinal cord, brainstem, and cerebrum.
• Synapse with granule cells in the granular layer.
• Transmit general sensory and motor information.
2. Climbing Fibers:
• Originate from the inferior olivary nucleus.
• Synapse directly on Purkinje cells (one-to-one relationship).
• Carry error signals for motor learning.

Output Pathway:

• Purkinje Cells:
• The only output of the cerebellar cortex.
• Inhibit deep cerebellar nuclei (dentate, interposed, and fastigial), which send excitatory outputs to motor pathways for movement coordination.