1. Understanding Circadian rhythms
Rooted in the Latin words "circa," meaning "around," and "diem," meaning "day," circadian rhythms are essentially endogenous, or internal, cycles that operate on a roughly 24-hour schedule. These rhythms are observed across many organisms, from plants and microbes to humans, regulating sleep-wake cycles, hormone release, eating habits, and numerous other physiological processes.
Background of Circadian rhythms
The scientific exploration of circadian rhythms can be traced back to the early 18th century when French astronomer Jean-Jacques d'Ortous de Mairan conducted experiments on the movements of Mimosa plants. He observed that the leaves of these plants opened during the day and closed at night, even when kept in continuous darkness, suggesting an internal mechanism at work. However, in the 20th century, researchers began to uncover the genetic and molecular mechanisms underlying these rhythms.
Genetic essence
In the 1970s, significant progress was made in discovering fruit flies' first circadian rhythm gene, termed "period" (per). This groundbreaking work demonstrated that circadian rhythms were not just behavioral phenomena but were genetically controlled. The molecular basis of circadian rhythms involves a complex interplay of proteins produced by circadian genes that interact within cells to generate and regulate rhythms. This system operates on a feedback loop mechanism where the production of specific proteins inhibits their production, leading to oscillations that align with the 24-hour cycle.
At the core of circadian biology is the suprachiasmatic nucleus (SCN), a tiny region in the brain's hypothalamus that serves as a master clock, synchronizing the body's internal clocks with environmental cues, primarily light. Light exposure to the retina influences the SCN, which regulates various bodily functions to align with day and night cycles. This entrainment to external light-dark cycles allows organisms to anticipate and adapt to the daily changes in their environment, optimizing physiological functions.