How to Visualize Something Really Small

This image shows a 3D reconstruction of a small dendritic protrusion, a filopodium, and its synaptic interaction with an axon. The axon (blue) is less than 0.5 microns in diameter. (As a comparison, a human hair is at least 70 microns in diameter.) The filopodium (brown) is less than 0.1 microns in diameter in some places. The synaptic contact (inset) is only about 0.1 microns in its largest dimension. Since the wavelength of visible light is itself about 0.5 microns, the true dimensions of such small structures cannot be observed with light microscopy. More complex procedures are required to visualize them. 

To visualize something this small, we begin with a small block of tissue containing the (even smaller) object. The tissue block is stained and embedded in epoxy. A small portion of the hardened block is shaved into a series of very thin sections, each about 50nm thick and 50 microns across, making a long ribbon of tissue sections.