Slide #DMS 098 [Cerebellum, monkey, PTS] In this slide, you are looking at small portion of the cerebellar cortex As you will find when you dissect the human brain, the cerebellum ("little brain") lies on the brain stem, largely hidden by the massive cerebral hemispheres It is largely concerned with the integration and coordination of complex motor activities Like the cerebral cortex, the cerebellar cortex has a complex organization related to its functional activities
Study the slide with the usual sequence from low to high power. At low power, you should have no difficulty now identifying, from outside in, pia mater [much of it artifactitiously torn away from the nervous tissue], gray matter, white matter The gray matter can divided into three relatively easily identified layers [see diagrams below] The superficial, outermost layer is the molecular layer It contains mainly dendrites and axons from cells in the deeper layers but only a few nerve cell perikaryia The middle layer is dominated by the cell bodies of peculiar giant nerve cells, the so-called Purkinje cells, arranged in a monolayer and is called, logically enough, the Purkinje cell layer The deepest layer, next to the white matter, is called the granular layer because it is packed with tiny the cell bodies of tiny neurons [granule cells] The Purkinje cells are the most interesting Not only are they huge [estimate the diameter of the cell body] but they have fantastic candelabra like dendritic trees that ramify in single plane in the molecular layer They are the only neurons that send their axons out of the cerebellar cortex and thus constitute the entire efferent outflow. Interestingly, the Purkinje cells contain GABA and they inhibit their subcortical target cells, as shown physiologically.
Cerebellum: Note the layers in this cerrebellar folia, with a core of white matter, a very prominent granular layer (small, blue nuclei) and the molecular layer (few neurons) at the surface. There is a single layer of Purkinji neurons at the interface between the granular and molecular layers (these can be seen at higher power).
This is a very low power view of a section through the cerebellum. Its very distinctive pattern of gray matter and white matter is easily appreciated.
At low power, one can define the three layer of the cerebellar cortex: the outermost molecular layer, the thin Purkinje cell layer, and the noticeably cellular granular layer. The white matter lies interior to the granular layer.
At high power, observe the large Purkinje cells positioned between the outer molecular layer and inner granular layer of the cerebellar cortex. The large nucleolus and cytoplasmic Nissl substance are apparent in the Purkinje cell at the top of the image. The large dendritic root of this cell type may be seen in the lower cell, though its further extensive arborization is best reveal with a Golgi-type stain (next slide).
At this medium power, note the numerous cell bodies belonging to the glial cells found within the white matter. The thick eosinophilic streaks seen in the image represent the largest nerve fibers (axons) enmeshed in a network of smaller caliber neurites and glial cell processes.