Layer It On

What am I looking at?

This is a cross section through the three layers of a mouse’s cerebellar cortex: the molecular layer is red (1), the so-called Purkinje layer is blue (2), and the granular layer is green (3). The red ovals at the junction between the molecular layer and the Purkinje layer (4) are the neuronal cell bodies of Purkinje cells. The red lines above those cell bodies (1) represent the dendrites extending from the Purkinje cells; the dendrites branch into a tree-like arrangement in the molecular layer.

Biology in the background

The outer region of the cerebellum is known as the cerebellar cortex and has a regular structure composed of the three layers you can see in this image. While there are a variety of cells present throughout these layers, they are mainly composed of two cell types: Purkinje cells and granule cells.

Purkinje cells have a distinct structure with a prominent cell body and a branching, treelike network of dendrites extending in one direction from the cell body. They are famous in the world of neuroscience because they were one of the first cell types to be visualized and drawn by early neuroscientists. Most of the Purkinje cell bodies reside in the aptly named Purkinje layer (the blue middle layer in this image). Their dendritic trees extend up into the outermost molecular layer.

The bottommost layer in the cerebellar cortex is composed mainly of granule cells – hence the name granular layer. These are some of the smallest and most numerous neurons in the brain. They receive input from the rest of the brain and then interact with Purkinje cells and other cells in the cerebellar cortex to carry out the many functions of the cerebellum.

In a mouse, a Purkinje cell body can be up to 30 micrometers across, or roughly 2.5 times smaller than the width of a human hair. Granule cell bodies are about 5 micrometers across, or roughly 15 times smaller than the width of a human hair.

Technique

This image was created using confocal microscopy.