The Human Brain : From Neurone to Nervous System

Neural Processing within the Cerebellum

  1. The cerebellar cortex has three layers -
    • the innermost, densely packed, Granular layer, consisting of the cell bodies of the granule cells
    • the surface molecular layer of Parallel fibres, consisting of the axons of granule cells
    • the Purkinje cell layer, one cell in thickness, between them, and situated so as to collect information from many parallel fibres

  2. The inputs to the cerebellum arise from two sites in the brainstem:
    • Mossy fibres originate in pontine nuclei and excite many granule cells, whose parallel fibres weakly excite Purkinje neurones.
    • Climbing fibres arise from the inferior olive of the medulla, and strongly excite a small group of Purkinje cells.

  3. Purkinje cell axons are the output pathways from the cerebellar cortex and inhibit neurones in the deep cerebellar nuclei; these neurone are also excited by collaterals of Mossy fibres and Climbing fibres within a functional unit.

  4. The cerebellum is divided into hundreds of independent functional units called modules. They share a similar basic structure, but each handles information from different sources, and relays its output to a different destination.

  5. Each cerebellar module handles information processed by a small linear area of cerebellar cortex called a microzone.

  6. These neural circuits combine somatosensory,visual and auditory information to detect errors in movement, i.e. any inconsistency between the motor command signal and the actual movement achieved

Key Words: Granule cells, Purkinje cells, parallel fibres; climbing fibres, mossy fibres; cerebellar module