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Why Do We Sleep?

Author: Jiahao Wu

Editors: Vincent Chang

Artist: Gianluca Zhang

Why do we sleep? What does it do to keep us healthy? Most importantly, what happens if we skip out on sleeping? Since we spend a third of our day on average doing it, sleep is more important than we realize. Quality sleep is just as important as food or water. Without sleep, pathways in your brain cannot be maintained and formed that allow you to learn and create new memories. However, biologically, we still do not understand the point of sleep.

Scientists have researched the areas of the brain that "create" sleep. The hypothalamus, a small, nut-shaped structure deep within the brain, controls groups of nerve cells that affect sleep and arousal.

Inside the hypothalamus is the suprachiasmatic nucleus (SCN), clusters of thousands of cells that receive information about light exposure, which controls your behavioral rhythm. Damage to the hypothalamus can result in erratic sleeping. The brainstem, located at the base of the brain, communicates with the hypothalamus and controls the switch to sleep and wake. This part also plays a role in REM sleep, sending signals to relax our muscles to ensure we do not act out our dreams. The thalamus relays information traveling from your sense

to the cerebral cortex, the part of the brain that interprets and processes memory. Normally, it is quiet during sleep, allowing you to tune out everything else. However, during REM sleep it sends images, sounds, and senses which become part of dreams. The pineal gland receives signals from the SCN and produces melatonin, a hormone that helps you sleep. People can stabilize their sleep patterns by taking small doses of melatonin. The basal forebrain and the frontal bottom of the brain promote sleep and awakeness. The release of adenosine helps support your sleep drive. Caffeine, a substance known to prevent tiredness and sleep, blocks adenosine’s function.

There are typically five stages of sleep. The first stage is known as light sleep, in which we drift in and out of sleep, and can be woken up at any time. Muscle activity is slow, and people awakened at this stage often remember fragmented visual images. During the second stage, our eye movements stop, and our brain waves become slower. In the third stage, extremely slow brain waves called delta waves begin to appear, along with smaller, faster waves. In the fourth stage, the brain almost only produces delta waves. Stages three and four are known as deep sleep, in which a person is not easily woken up. When we switch to REM sleep, our breathing becomes rapid, irregular, and shallow. Eyes move in various directions, and limb muscles are temporarily paralyzed. When people wake up from REM sleep, they usually can “remember” their dreams. A complete sleep cycle of REM takes about 90-110 minutes on average. At first, the sleep cycles contain short REM periods and long periods of deep sleep. As time goes on, REM sleep periods become longer while deep sleep becomes shorter. By morning, people have spent their sleep time in stages 1, 2, and REM.

Although significant research has gone into sleep, what happens when you do it, why it is necessary, and the reason for why it exists is still a mystery. Considering how humans use a third of their day to sleep, it must hold an important function that we have not discovered yet. Hopefully, we will crack this question in the future.



Pappas, Stephanie. “Why Do We Sleep?” LiveScience, Purch, 18 July 2017,

ASA Authors & ReviewersSleep Physician at American Sleep Association

Reviewers and

WritersBoard-certified sleep M.D. physicians. “What Is Sleep and Why Is It Important?”

“Brain Basics: Understanding Sleep.” National Institute of Neurological Disorders and

Stroke, U.S. Department of Health and Human Services,

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