A cross section of a bundle of nerve fibers. Axons (orange) are wrapped in myelin (purple); an extension of the membrane of glial cells. Myelin has high lipid content, and acts to insulate the axons, causing them to transmit nerve impulses much faster.
In yellow, bacterial plaque on the surface of a tooth. The acid produced as waste during bacterias' digestive process demineralises the tooth creating cavities that will need fillings or may lead to tooth lost.
The hydrothermal worm is so tiny it requires a powerful microscope to see it. The organism, only slightly larger than a bacterium, lives in deep sea near hydrothermal vents that spew hot water from beneath the Earth’s crust. Photo by Phillippe Crassous.