Researchers originally assumed the body contained but a single molecular clock (buried deep within the brain) that was responsible for synchronizing key physiological functions with the 24-hour cycle of a day on Earth. But as Keith Summa and Fred Turek write in the February Scientific American, the body actually has many cellular clocks scattered throughout its tissues—in the liver, pancreas and elsewhere. Disruptions in any of the secondary clocks may increase an individual's risk of developing heart disease, diabetes or depression, among other conditions.

The following video provides a 20-minute overview of what researchers have so far discovered about how all life on Earth—and especially mammals like ourselves—keep time. The video focuses on the work of longtime neuroscientist Joseph Takahashi, who currently heads a lab at the University of Texas Southwestern Medical Center in Dallas. Takahashi and Turek were both members of the team that in 1997 isolated the first circadian gene in mammals.

Among the more intriguing visuals is a time-lapse recording of the master clock ticking seconds away inside the brain. (The recording actually represents the fluctuations of a particular protein that turns certain genes on or off, depending on whether it is light or dark outside.) But as Takahashi makes clear, this kind of timing mechanism is found in almost every cell of the body—which he nicely illustrates with another video of skin cells oscillating on and off.

Something to think about the next time you decide to disrupt your biological clock by staying up late staring at your smartphone.