Author: Branden Chen
Editors: Lydia Ren and Cynthia Zhang
Artist: Jiaqi Fan
Humans sleep—it’s just a natural process everyone goes through. But, why do we sleep at night and remain awake during the daytime? The answer lies in the biological mechanism present in our body known as the Circadian Rhythm. This biological clock is the physical, mental, and behavioral changes in our bodies that follow a 24-hour cycle, adjusting to the light and dark. This cycle is not only present in humans, but also animals, plants, and even microbes. It is essential to know how not to disrupt our circadian rhythm, as it can negatively affect our daily lives.
The circadian rhythm is regulated through “clocks” in our bodies, known as biological clocks. These clocks consist of proteins that interact with cells throughout the body and are present in almost every tissue and organ. All of these biological clocks are maintained by one clock: the master clock. Present in the brain, it keeps all of the biological clocks in sync and ensures the efficiency of these processes. In humans and other vertebrate animals, this master clock is composed of approximately 20,000 neurons that form the SCN, or the suprachiasmatic nucleus. The SCN is a part of the hypothalamus and receives electrical impulses from the eyes. In relation to the circadian rhythm, the SCN controls the release of melatonin, the hormone responsible for feelings of sleepiness.
Although the sleep-wake cycle is the most common example of a circadian rhythm, natural bodily factors also produce other circadian rhythms, such as the body-temperature cycle and the hormone release cycle. The genes that govern the circadian rhythms in the human body are the Period and Cytochrome genes. When we sleep, these genes encode proteins that build up during the night in a cell’s nucleus and then lessen during the day. Research has shown that these genes may be responsible for feelings of alertness and sleepiness. Light plays a crucial role in these genes, where exposure to excessive light at a different time of day can alter when the body activates the Period and Cytochrome genes. Referring back to the previous example of melatonin, the eyes rely on information received from surrounding light to the brain. For example, if it is dark, the SCN will increase the output of melatonin into the body.
Environmental factors can alter our circadian rhythms as well. Jet lag is a typical example of shifting our biological clock. For instance, if you traveled from the West Coast to the East Coast in the US, the time zone changes by three hours. So, if you wake up at 7:00 AM in New York, your biological clock may still be stuck in your previous time zone with your body believing that it is still 4:00 AM. This change will cause your biological clock to reset, but this adjustment typically takes a few days.
So why is it so important to know about our circadian rhythm? Studies show that our circadian rhythms affect our mental health as well, so disrupting this cycle can increase the risk of depression and other psychiatric illnesses and potentially neurodegenerative diseases, such as dementia. Research has also linked the circadian rhythm to our physical health, affecting metabolism and weight and the regulation of blood sugar and cholesterol. With all this knowledge in mind, it is vital to maintain an individual’s biological clocks through efforts such as exercise, sleep, and exposure to natural light during the day.
Citations:
Circadian Rhythms. (2019). Nih.gov. https://www.nigms.nih.gov/education/fact-
sheets/Pages/circadian-rhythms.aspx
What is Circadian Rhythm? | Sleep Foundation. (2021, January 29). Sleep Foundation.
https://www.sleepfoundation.org/circadian-rhythm