Most stem cells go where the bloodstream takes them. MUSE cells (Multilineage-differentiating Stress Enduring cells) go where the damage is.
 
This rare, non-tumorigenic subpopulation of mesenchymal stem cells senses sphingosine-1-phosphate, the universal distress signal released by injured tissue, travels directly to the site, and becomes the tissue type it finds there. It's why researchers in Japan have studied them across the heart, brain, kidneys, and spinal cord, and why the published work below is worth your time.