Climbing fibs.

Mossy fibs.








Circuitry within the Cerebellum

Now that we know the various inputs to the cerebellum (DSCT, CCT, OCT, VCT, and PCT [2 parts]), and where they go (med., intermed., lat., flocc. nod. lobe), we need to consider some internal cerebellar circuitry over which the incoming information is processed before being sent out of the cerebellum to other motor centers.

Before looking at the internal cerebellar circuitry, we need to examine how all of the little cerebellar folds or gyri, called folia (singular = folium) are organized. In the drawing below to the left are 3 isolated cerebellar folia. From the extracted tissue block at the right you can see that these folia can be sectioned either PARALLEL to their LONG axis or TRANSVERSE to their LONG axis. Each single folium is comprised of an outer cerebellar CORTEX (bark, peel, husk), which contains three cell layers, molecular, Purkinje, and granule. This cerebellar cortex overlies a deep zone of efferent and afferent fibers that we just call white matter. Within this dense aggregation of millions of fibers lie three sets of deep cerebellar nuclei (dentate, interpositus and fastigial). These deep nuclei ARE NOT shown in the drawing below, but we have already heard about the dentate and interpositus nuclei when discussing the superior cerebellar peduncle (Point 18). We will return to these nuclei later in the story!!

You can see that the dendrites of the Purkinje cells (the most popular cells in the cerebellar cortex) are oriented TRANSVERSE or perpendicular to the LONG axis of the folium. Spread your fingers out and look at your palm. You are now looking at how a Purkinje cell dendritic tree looks when the folium is sectioned TRANSVERSE to its LONG axis.

Now, rotate your hand 90o and see how the dendritic tree of that same Purkinje cell looks when the folium is sectioned PARALLEL to its LONG axis. Sadly, you do not see the full extent of the Purkinje cell dendritic tree from this view!! This is shown below.