Rock Around the Clock by Bill Haley & His Comets became a worldwide hit in the 60s. At about the same time, science coined the term circadian rhythm. Is that just a coincidence? Yes, almost certainly. But we still want to keep in mind the common factor, namely "clocks". The history of timekeeping devices goes back several millennia. It wasn't always the fancy wristwatch that made it possible to measure time intervals or define points in time. In around 3000 BC, for example, the Sumerians used simple shadow sticks as part of a sundial. Can the history of the clock be traced back even further? Historically, no, biologically, yes.
The very first clock was actually us humans. To be precise, probably all forms of life before us, but we don't want to lose sight of the essentials. The clock, however, was not made of gold, silver and diamonds, but of hormones and proteins. It still is and we call it internal clock or circadian rhythm.
What does circadian mean?
The adjective “circadian” comes from Latin and can be understood as “around the day” or “about a day” (lat. circa “around…”; dies “day”). Over the course of a day, the conditions of our environment vary constantly. Specifically, the amount of light, the temperature and also the availability of food change. All of this happens on Earth with an approximate period length of 24 hours – about one dayIf living beings can adapt to these drastic changes, they have a survival advantage.
In fact, we don't just have one internal clock, but millions of small timepieces. Practically every cell in our body has its own clock. Our "internal clock" has the task of synchronizing these numerous clocks with each other. This is important in order to give the variety of chemical reactions a time frame - not all chemical reactions fit into the program at the same time. In a similar way, no major broadcaster broadcasts blockbusters on all channels at the same time. That would be less than satisfactory for customers.
There are other rhythms that do not follow the 24-hour periodicity. Infradian rhythms last significantly longer than a day and include, for example, the sexual cycle or reproduction in humans. In contrast, ultradian rhythms with a period length shorter than one day. These include heartbeat, breathing or sleep phases.
Jet lag – when the internal clock starts to react
What some people find soothing drives others crazy: the periodic "tick, tock" of analogue clocks. This is not an issue with timepieces made of flesh and blood, because we don't hear our internal clock ticking. In fact, we don't notice any of the regulatory processes at all, at least as long as everything is working properly.
The Circadian rhythm must be constantly resynchronizedIn the 19th century, this was mainly due to the changing length of the day, a consequence of the change of seasons. Then came the airplane and long-distance flights. This requires a very short-term adjustment of the circadian rhythm. The initial lack of agreement between time zone and internal clock manifests itself in us as jet lag. The Time zone hangover manifests itself through insomnia, tiredness, loss of appetite or mood swings. It is also interesting to note that the direction of flight plays a role. Flights to the west are generally better tolerated than flights to the east.
To cope with the potentially very stressful symptoms, there are a few general recommendations for behavior:
– participate in the daily rhythm of the destination
– spend a lot of time outdoors – light is the most important pacemaker
– get enough sleep without aids such as sleeping pills or alcohol
Now nothing stands in the way of the next transatlantic flight!
The Aschoff rule – permanently light and permanently dark
If external time cues such as light to set the internal clock are missing, animals change their behavior. This very interesting observation was made by the behavioral physiologist J. Aschoff in the 1960s. In diurnal animals, the internal clock runs a little faster under constant artificial light. If, however, it is constantly dark, then the rhythm is slowed down. The opposite is true for nocturnal animals. In various specialist books, this peculiarity can now be found under the term Aschoff rule.
How does the circadian rhythm work?
Basically, our internal rhythm works independently of external factors. However, the process can adapt to a more or less precise 24-hour cycle with the help of so-called timers. This process is also called Synchronization. The most universal and important timekeeper for our internal clock is probably the Lighting. Ambient temperature and social stimuli also play a role.
The synchronization is carried out by special receptors in the retina of the eye. These cells transmit signals to the Nucleus suprachiasmaticus in the hypothalamusThis is the central control point of our internal clock, through which body temperature, heart rate, blood pressure, hormone levels and many other bodily functions are regulated. Other peripheral pacemakers are timed from this brain core. In the brain, the brain also plays a role in the Melatonin an important role in the regulation of the sleep-wake rhythm.
Several Gene control an extraordinarily complex Interaction of transcription and translation the rhythm. As a reminder: transcription is the copying of genetic information and translation is the translation of DNA language into proteins. The interaction involves feedback loops that regulate themselves and take about a day. Sounds complicated - and it is. A detailed discussion of the regulatory loop would go beyond the scope of this text.
When the clock gets out of sync
Our biorhythm is not only important, but since 2017 it has even been Nobel-important. At that time, the scientists Jeffrey C. Hall, Michael Rosbash and Michael W. Young received the Nobel Prize in Medicine and Physiology due to the discovery of molecular mechanisms that control biorhythms. They gained their knowledge using the fruit fly as a representative of other species.
The importance of this topic affects every single person. If we live against our internal clock for a long time, the risk of cancer, neurological and metabolic diseases or depression can increase. Rock Around the Clock It is therefore better for it to remain just music in our ears and not a way of life.
Sources
- https://www.spektrum.de/lexikon/biologie-kompakt/aschoff-regel/948
- https://www.nobelprize.org/prizes/medicine/2017/summary/
- Herxheimer, A. (2014). Jet lag. BMJ clinical evidence, 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4006102/
- Roenneberg, T., Kuehnle, T., Juda, M., Kantermann, T., Allebrandt, K., Gordijn, M., & Merrow, M. (2007). Epidemiology of the human circadian clock. Sleep medicine reviews, 11(6), 429-438. https://doi.org/10.1016/j.smrv.2007.07.005
- Ko, CH, & Takahashi, JS (2006). Molecular components of the mammalian circadian clock. Human molecular genetics, 15(suppl_2), R271-R277. https://doi.org/10.1093/hmg/ddl207
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