Lab 8 - Higher Motor Function

Microscropic Anatomy

View and identify the structures in the illustration.

The innermost layer is composed of granule cells and is called the granule cell layer. A middle layer (which is one cell in thickness) contains Purkinje cells and is called the Purkinje cell layer. Purkinje cell axons are the sole output of the cerebellar cortex. The outermost layer is called the molecular layer. The molecular layer contains three types of interneurons, named Golgi, basket and stellate cells. It also contains fan-like dendritic arbors of the Purkinje cells (all arranged in parallel in a rostral-caudal orientation) and the axons of the granule cells.

The granule cell axons are called parallel fibers. In the molecular layer, they run parallel to one another and perpendicular to the plane of the Purkinje cell dendrites. The parallel fibers synapse on the dendritic spines of the Purkinje cells.

The Purkinje cell can be easily identified by its large dendritic tree in tissue prepared by the Golgi method. Recall that the Golgi method colors only a few selected neurons in a given section and colors those neurons in their entirety, i.e., the cell body, axon and dendritic processes.

Although the cerebellar cortex receives highly varied inputs from diverse sources and has both ascending and descending projections, the cellular organization of the cerebellar cortex is remarkably uniform. Throughout the cerebellar cortex, two fiber types provide input: mossy fibers (of widely varied origin) synapse with cerebellar granule cells and Golgi cell interneurons; climbing fibers (which originate in the contralateral inferior olive) synapse directly on Purkinje cells.

Whereas mossy fibers convey sensory and motor command information to the cerebellum, the climbing fibers are believed to be important in conveying movement errors and in inducing long lasting changes in cerebellar synapses, resulting in motor learning.