More than just a rigid organ, bone is porous and has living cells. Knowing the structure of bone is key to understanding how nutrients are delivered and the signals transmitted between bone cells. Using fluorescence, the network of bone cells is imaged under a microscope. The vast branch-like structures (upper left) are dependent highways of isolated bone cells. And bone cells form a solar system-like structure, following pink traces of collagen in cross sections (bottom left). On the right, a longitudinal section shows the connection of blood vessels and bone cells, illustrating the nutrient supply system (blue shows cell nuclei).