Neurons from stem cells, fluorescence light micrograph. Stem cells are able to differentiate into the many cell types in the human body. The type of cell they mature into depends upon the biochemical signals received. In this case, they have matured into neurons (nerve cells) from the brain's cortex (cortical neurons). They were derived from induced pluripotent stem cells (iPSC). Developing neurons have long neurites filled with bundled microtubules that terminate in actin-rich growth cones. The longer these neurons develop, the longer and thinner the neurites become. These cells have been stained for actin (cyan), microtubules (orange) and cell nuclei DNA (blue). These neurons are shown on day 1 of development. For a series of images showing stem cell neurons after 1 to 5 days of development, see images C048/1344 to C048/1351.