Written by Shreya Sharma
Even though sleep is just as essential as regular exercise and a balanced diet,
over 35% of adults report getting less than the daily recommended hours of sleep. The brain relies on sleep to remove toxins built up during waking hours, help neurons exchange signals, strengthen the mind and body, and support every bodily system. However, humans continue to remain the only species that willingly delay sleeping.
Chronic sleep deprivation is linked to increasing the risk of high blood pressure, diabetes, mental health issues, cardiovascular disease, depression, and various other health issues.
Modern technology is providing new avenues for scientists to discover more and more about the complexities of sleep.
Sleep can be divided into three basic categories, rapid eye movement (or REM), sleep and non-REM sleep. Each stage of sleep is associated with a particular set of brain waves. In a typical night, an individual will cycle through the stages multiple times, with more extended REM periods towards the morning. Stage 1 non-REM marks the very short transition from wakefulness to light sleep. Here, the breathing, heart rate, eye movements, and brain waves begin to slow down as the muscles relax. Next, stage 2 non-REM is the duration of light sleep before entering deep sleep, occurring mostly throughout the first half of the night. In this stage, the body’s temperature decreases, eye movements slow down, and the brain activity is slow, with intermittent periods of electrical activity. The final stage of non-REM sleep, stage 3, is the period of deep sleep in which heart rate and breathing are at their lowest, and brain waves are even slower than the previous stage.
REM sleep is very different- the frequency of brain waves is similar to waking rates, breathing is faster, heart rate and blood pressure increase, and the eyes move rapidly behind the eyelids.
This phase first occurs approximately 90 minutes after falling asleep, and most of the dreaming occurs at this stage. Interestingly, temporary paralysis of the arm and leg muscles arise at this point, preventing the dream’s enactment. Additionally, an individual spends less time in REM sleep as they age.
The natural regulation of sleep occurs via two biological mechanisms. The first is the circadian rhythm, which directs periods of wakefulness, metabolism, body temperature, and hormone release. This system is responsible for the tendency to experience tiredness at night, as well as the tendency to wake up around the same time each morning. Environmental cues, such as temperature and light, are synchronous with circadian rhythms. However, the process continues even without the signals. The second biological mechanism is sleep-wake homeostasis, which tracks an individual’s need for sleep. This reminds the body to sleep after a specific period of time, as well as the intensity of sleep necessary. The drive of sleep-wake homeostasis increases in strength with each passing hour, causing one to sleep longer and deeper after experiencing relative sleep deprivation.
Light exposure influences the “internal clock” using specialized cells in the retinas. These light-sensitive cells are found in the same space as the eye’s rods and cones, and use light to inform the brain whether it is night or day. The sleep patterns are adjusted accordingly to this. The phenomenon of jet lag occurs due to variations in light exposure and the subsequent disturbances in the circadian rhythm and sleep-wake homeostasis.
Various genes and neurotransmitters also play a crucial role in controlling sleep. As an individual prepares to go to sleep, sleep-promoting neuron clusters in several parts of the brain are activated. Neurotransmitters such as GABA, or gamma-aminobutyric acid, are associated with sedation and muscle relaxation. Additionally, orexin (or hypocretin) and norepinephrine keep different parts of the brain active. Acetylcholine, histamine, serotonin, and adrenaline also help manage sleep and wakefulness. Clock genes control the circadian rhythm, while others can regulate neuron excitability. Genome-wide studies have shown various chromosomal sites that are linked to increasing sleep disorder susceptibility.
Furthermore, genetics have been found to play a role in narcolepsy, advanced sleep-phase syndrome, and restless legs syndrome.
Different genes in areas of the brain, such as the cerebral cortex, change their levels of expression depending on the individual’s state of sleep or awake-ness. The worm, fruit fly, and zebrafish have been particularly useful in recognizing molecular mechanisms and variants in genes that result in healthy and, alternately, disordered sleep.
Today, scientists are advancing what they know about the regulation and importance of sleep. Much of modern research is dedicated to understanding the relationship between chronic sleep deprivation and disease. By learning more about the role of sleep, or lack thereof, plays in the development of infections, cancers, and other diseases, potential treatments and prevention plans can be implemented. Additionally, sleep disturbances are prevalent amongst older individuals with neurological disorders such as Alzheimer’s and Parkinson’s disease, but the association is not yet understood. While further research is in progress, there is ample proof that sufficient sleep will lead to a healthier, well-rounded life.
References
Brain Basics: Understanding Sleep. (2019, August 13). Retrieved August 12, 2020, from
https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep
External Factors that Influence Sleep. (2007, December 18). Retrieved August 12, 2020, from
http://healthysleep.med.harvard.edu/healthy/science/how/external-factors
Serin, Y. (2019, April 23). Effect of Circadian Rhythm on Metabolic Processes and the
Regulation of Energy Balance. Retrieved August 12, 2020, from
https://www.karger.com/Article/Fulltext/500071
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