Circadian Rhythms: The Conductor of Our Body’s Symphony

Circadian Rhythms: The Conductor of Our Body’s Symphony

Our bodies are like musical compositions, different instruments completing the whole piece. The heart is the percussion, keeping pace for the rest of our bodies. The digestive system is the bass, providing the foundation everything else body systems need. The brain is the piano, giving us life and coordination. But who is the conductor? To whom do we owe the perfect synchronization of all instruments? The mastermind may come as a surprise, but the miracle-worker of our bodies’ symphony is the circadian clock — a series of molecular cues which integrate external stimuli to keep our bodies’ cycles on a 24-hour schedule.

Our mastermind’s lair is a compartment of the brain called the suprachiasmatic nucleus (S.C.N.), containing only 50,000 of the 86 billion neurons in our body. Our eyes detect light, signaling directly to the S.C.N., as if the conductor were being cued by the mood of the audience. During the day, high intensity light signals the S.C.N. to produce the proteins period (Per) and cryptochrome (Cry), which in turn activate myriad downstream pathways controlling metabolism, sleep and overall activity level. Meanwhile, Per and Cry accumulate in the cytoplasm, reaching critical levels at which they translocate to the nucleus and bind to receptors that shut down the production of Per and Cry. This slows metabolic activity and prepares the body for sleep.

This diurnal feedback loop is the crux of homeostasis, or biological equilibrium, but all musicians know what can happen when the conductor of the orchestra misses a beat. For instance, when we experience jet lag after flying between different time zones, our circadian rhythms are disrupted because our S.C.N.s receive light signals that are out of register with our previous protein accumulation cycles.

Additionally, circadian rhythm disruptions have been linked to obesity. Scientists compared light pollution data across the United States, and brightly-lit urban areas have significantly higher obesity rates. Further studies revealed that a hormone called leptin, responsible for appetite suppression, is regulated by the circadian clock. During the day when activity and energy requirements are increased, leptin expression decreases and thus we eat. When our circadian clocks are disrupted, leptin expression is lower, resulting in abnormally increased appetite and obesity.

A dive into the rhythmic inner-workings of our bodies can help explain why you have a bad night’s sleep after watching Netflix late at night, or why staying inside all day makes you less hungry. Dysregulated circadian rhythms may cause neurological disorders including Alzheimer’s disease, so further study of this symphony may offer potential treatments. Now, as the orchestra quiets and the conductor bows, scientists applaud the small compartment of our brain that keeps our bodies in sync.

Works Cited

Fonken, Laura K., and Randy J. Nelson. “The Effects of Light at Night on Circadian Clocks and Metabolism.” Endocrine Reviews, 1 Aug. 2014.

Froy, Owen. “Circadian Rhythms and Obesity in Mammals.” ISRN Obesity, 18 Nov. 2012.

“Jet Lag — Overview.” American Academy of Sleep Medicine.

Ko, Caroline H., and Joseph S. Takahashi. “Molecular Components of the Mammalian Circadian Clock.” Human Molecular Genetics, 15 Oct. 2006.

Nagourney, Eric. “Some Rhythmic Clues to Alzheimer’s.” The New York Times, 17 April 2001.

Sanders, Laura. “Out-of-Whack Body Clock Causes More Than Sleepiness.” Science News for Students, 3 Dec. 2019.