Abstract:
Sleep is an evolutionarily conserved process, seen from small insects to the biggest mammals. Many questions surrounding this enigmatic process are- why do we sleep? How does our body know when to sleep? Where is our master clock located? What are its characteristics etc? Researchers believe that sleep should have an essential, irreplaceable function if it was not lost to evolution. Yet we do not have an accurate understanding of its functions. A lot of research is being conducted to understand how sleep affects various physiological functions of the body.
Keywords: Sleep, Circadian rhythm, Suprachiasmatic Nucleus, Sleep pressure
For many years, people believed that sleep was a luxury, and the common saying used to be “If you work hard now, you can enjoy a good night’s sleep later.” However, mounting evidence and research emphasize the importance of “sleep now for a healthier tomorrow.” This opens up a plethora of questions like- Why do we even sleep? Are we the only species that sleep? Or do small insects and fishes also doze off? What functions does sleep serve? Apart from these, there is an entire realm dedicated to unravelling the mysteries of dreams and their purpose. What is more bewildering is that most of these questions remain unanswered.
We all mostly fall asleep at night. But how does our body know that we need to go to sleep? There are two main factors we have to consider here (1) the internal clock or the circadian rhythm and (2) the chemical signals that induce sleep pressure (Walker, 2018). Let us briefly understand these two factors, which are the essential characteristics of sleep.
Circadian rhythm comes from the Latin words circa, meaning ‘about’, and dies, meaning ‘day’. It is a 24-hour clock generated internally, which is then synchronized to external stimuli, like light patterns due to the earth’s rotation (Russell G. Foster, 2020). When the internal and external clocks become desynchronized, we experience something like Jet lag. Our internal clock, called the Suprachiasmatic Nucleus (SCN) is seated deep within the brain’s hypothalamus. Each tissue and organ in our body has its own biological clock, but SCN acts as the master clock, coordinating all these peripheral clocks and bringing about the overall 24-hour sleep-wake cycle.
The other factor that determines when to go into slumber is the sleep pressure, which is communicated through chemical messenger- Adenosine. With each wakeful minute, adenosine molecules accumulate in the brain, increasing the desire to sleep. This process is termed the homeostatic control of sleep (Russell G. Foster, 2020). Such sleep pressure is usually experienced after a sleepless night when we are extremely sleepy even though our internal clock tells us it's not the time to rest. During such times, a caffeinated drink would surely wake us up. So how does caffeine kill your sleep desire? Caffeine is a molecule that is similar to adenosine. Caffeine binds and blocks the adenosine receptors. This temporarily reduces the sleep pressure and makes us feel energized (Summer & Vyas, 2022).
There is the other messenger molecule, called melatonin which is usually referred to as the sleep hormone, although it does not have any role in the sleep process. It is released by pineal glands, which is regulated by SCN. Thus the concentration of melatonin increases during the night (Russell G. Foster, 2020).
On average humans sleep between 5 to 10 hours a day which makes up one-third of their lives (Walker, 2018). While African elephants sleep 3 to 4 hours a day. On the other hand, armadillos sleep 18 hours per day (Keene & Duboue, 2018). Despite the difference in sleep durations of various species, most of the species ranging from fishes (Saey, 2019) to insects (Förster, 2018) to mammals, have demonstrated to have sleep-like states. At first glance, it might seem like a harmful behaviour. Because during sleep, animals are more vulnerable to predation, and they cannot gather food nor reproduce (Dissel, 2020). In spite of all these risks sleep should serve some essential and irreplaceable function, as it is evolutionarily conserved.
Many theories about the functions of sleep have been proposed to date. Researchers agree that sleep is essential for a variety of physiological processes like development, energy conservation, immune response, brain waste clearance, cognition, memory formation, and other psychological conditions (Zielinski et al., 2016). There has been a lot of research conducted in this field to uncover the mysteries of sleep. As we are in an era where sleep loss has become a global health epidemic (Chattu et al., 2018), it is even more important to understand the mechanism of sleep and its various functions.
In conclusion, sleep is a complex but essential phenomenon. Remember that sleep is not a luxury, it is a necessity. In this fast-paced world, it is essential to recognize and prioritize your sleep, for all we know, dozing off can give you a healthier tomorrow.
REFERENCES
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About the author
I am Mrudula G, a Biology graduate from Azim Premji University, Bengaluru, India. My honours project dealt with “Effects of sleep deprivation on food preference in Drosophila melanogaster”. Presented a poster at the Indian Neurobehavior Conference, 2022 (Indian Neurobehavior Conference). Through this opportunity, I developed a deep interest in the biology of sleep and neuroscience. I am equally passionate about science communication, striving to help lab science reach the general public. I am an avid reader with a penchant for fantasy romance novels and love to crochet. Additionally, I find solace in K-Dramas and C-Dramas.
Linkedin- linkedin.com/in/mrudula-g/
Instagram- @_mystic_life
Editor: Himanshi Yadav