This morning Jeffrey Hall, Michael Rosbash, and Michael Young were awarded the 2017 Nobel Prize in Physiology or Medicine for their work on circadian rhythms. How do these 24-hour internal clocks work? Here’s a peek at what’s going on in the brain at the molecular level, as drawn by Cynthia Turner for the article “The Tick-Tock of the Biological Clock,” by Michael Young (Scientific American, March 2000). Check out the full article for more graphics.

CREDIT: Cynthia Turner