The Beautiful Cerebellum

Okay, guilty as charged. It’s been a while since my last post, but in my defense, I’ve been dealing with a lot of midterms recently. Yeah, that’s right. I may have graduated college but I’m still finishing up pre-med coursework. My most recent exam was in Histology, which is turning out to be a pretty cool class.Histology is basically microscopic anatomy. By chemically fixing body parts, embedding them in wax, slicing into them into thin sections, and finally staining them with dyes like hematoxylin and eosin, it’s possible to observe the structure of organic tissue with a light microscope. My professor has introduced our class to an amazing online repository of histological preparations hosted by the University of Iowa.

One of my only complaints about the class is that we focus almost exclusively on structure, without much attention to function. This is an unfortunate consequence of time limitations, but sometimes I go out of my way to follow up on a specific topic. Usually learning the functional organization of a given tissue also makes it much easier to memorize the structural organization. Take, for instance, the structure of the cerebellum:


Memorizing these layers is not too challenging, but I found some functional diagrams that helped me make sense of this brain system. This one from the University of Illinois does a nice job of showing synaptic connections between the layers:

Here we can see that the Purkinje cells (the large, sparsely populated cells in the Purkinje Layer) are receiving synaptic inputs from a multitude of granule cells below them. Granule cells are present in great abundance, making up 70% of the body’s neurons. While a single Purkinje cell receives hundreds of thousand synaptic connections from granule cell parallel fibers, they receive input from only one climbing fiber. This second type of connection is quite potent, capable of inducing complex spike trains in postsynaptic Purkinje cells. In contrast the Granular Layer, the Molecular Layer is dominated by inhibitory interneurons with horizontal processes.

The structure of the cerebellum is actually quite elegant. Here is one more photo in which Purkinje cells are tagged with a fluorescent dye. It makes their intricate dendritic trees very apparent:

Link to an extensive Wikipedia article on the cerebellum.

Link to the Univerity of Iowa virtual slidebox.

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