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Yawning and an Introduction to Sleep

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    Yawn. There, I said it. And I even provided an image (Figure I.1). Now you will likely be yawning for the next few minutes, and if anyone sees you reading my book, they will say, “I’m not going to pick up that book! Boring, eh?” But hopefully, you will find sleep science irresistible enough that you will join me in engaging people in conversations about sleep, its truths as well as its myths—such as boredom being the cause of yawning.

    Little girl yawning.
    Figure I.1 Yawning

    Why am I so passionate about sleep—talking about it, teaching college lecture and lab courses about it, giving workshops around the world about it? It goes way beyond how fascinating some things about sleep are, such as

    • • the meaning of dreams and nightmares (Figure I.2)
    • • animal sleep and behaviors like sleeping while swimming or flying
    • • disorders such as teeth grinding, sleepwalking, and sleep paralysis

    Yes, these are compelling topics, and I cover them all and much more. But my passion? It comes from my fierce commitment to helping people determine how they can do two things:

    1. 1. Improve their sleep and enjoy the associated health benefits
    2. 2. Find their place in creating a revolution so more people will understand sleep’s importance and have the opportunity to get enough of it
    Floating high above land is an open book with water pouring off the pages.
    Figure I.2 Dreams

    Sleep quality is one of the strongest predictors of how long you will live and how good you will feel, mentally and physically. In most circumstances, sleep quality can be a stronger predictor of longevity than diet, blood pressure, cigarette use, or genetics (Figure I.3). Healthy sleep changes which of your genes are expressed. Combine this with the fact that good sleep causes changes in brain physiology that make it easier to create healthy habits such as quitting smoking, improving food choices, and getting exercise and the case for prioritizing sleep becomes even clearer.

    While you sleep, there are changes in your brain, cardiovascular system, and metabolism as well as your body’s healing pathways. Most of us have noticed the slow thinking and crankiness associated with poor sleep, but did you know your brain is taking out the garbage while you sleep? During sleep, a set of structures that comprise the glymphatic system flush out toxins and waste associated with an array of neurologic problems.

    To keep your heart and blood vessels healthy, your body will also need sleep. It is essential to blood pressure regulation. Sleep reduces the risk of cardiovascular disease and stroke. Many people, hoping to avoid a myocardial infarction (heart attack), try to manage their health with foods, and that is a good idea, but they would be wise to also address their sleep as if their lives depend on it—because they might.

    105 year old woman.
    Figure I.3 105 year old woman

    Sleep is crucial for maintaining a balanced metabolism and managing appetite, blood sugar, and diabetes. This is related to poor sleep’s effect on hormones, which can make you feel as though you are starving even though you have eaten plenty. Insulin sensitivity (related to diabetes) also takes a drastic turn for the worse if someone is not getting enough sleep.

    Inflammation and oxidation, recognized more commonly in relation to injuries and healing, are also underlying mechanisms in many diseases, including several neurologic disorders. We will see that sleep is essential for reducing oxidation and inflammation and promoting healing, reducing pain, and lowering risk for neurologic disorders (Figure I.4).

    Outline of human body with list of effects of sleep deprivation.
    Figure I.4 Some of the effects of sleep deprivation

    We know that sleep provides a spark for creativity and problem solving as well as laying down the physiological changes for learning and memory. While there are numerous stories such as how the melody of “Yesterday” came to Paul McCartney in a dream, that type of inspiration translates to most of us as solutions to the previous day’s problem that become apparent after “sleeping on it” (Figure I.5). This common (and wise) expression alone, and its existence across cultures, points to the now scientifically based fact that sleeping and dreaming help us create solutions and solve problems.

    There is a tragic catch. Who has the luxury of putting into practice the recommendations of the numerous healthy sleep articles going around? Who of those in society can carve out eight hours each night in a quiet, dark, comfortable, temperature-controlled room? It is painful to see the studies showing correlations between poor sleep and race, sexual orientation, economic group, and education level.

    Collage of images of music sheets, periodic table, and DNA strand.
    Figure I.5 Sleeping on it

    The majority of those who get good sleep are already at an advantage based on race, sexual orientation, economics, and education. If the research continues to pile up showing the connection between good sleep and being smarter, faster, stronger, and more successful, we must take responsibility and address the sleep wellness gap. There is an essential element of social justice, antiracism, and inclusion work in sleep science, so in each chapter, we will discuss this and provide ideas for how you can have an impact in your community and beyond. I have also dedicated a chapter to equity, politics, and sleep. As Zoë Heller has asserted in her New Yorker article, “The fact that some of the leading indicators for poor sleep and sleep loss are low household income, shift work, food insecurity, and being African-American or Hispanic suggests that the quest for rest is not so simple.”1 Let’s get together, put the information from this book in motion, and create a sleep wellness revolution. I invite you to work with me to achieve that dream.

    But what about yawns? Oh, there you go again. Yawning at my book. The good news is, if you catch yawns, that it is an indication you are empathic. Empathy is the ability to share and understand another person’s feelings, so it is a treasured quality—one that is correlated with the contagiousness of yawns. To back this claim up with the behavioral evidence, brain imaging studies show that the areas of the brain activated during yawning are associated with understanding others’ feelings. Yawning is typically not contagious in children under five years old, as they are still building their capacity for empathy with each year. Yawning’s contagiousness may be valuable as a signal among animals to coordinate behavior—for example, as a way to say, “It is time for all of us to go to sleep.”

    Contagious yawning could also help a group react quickly to a sudden increase in temperature. Disproving earlier theories that yawning is a response to low oxygen, the current research suggests yawning’s purpose is to cool the brain. So when one animal yawns, others nearby might begin yawning too because if one of them is getting warm, the rest will soon be in need of the brain-cooling benefit of a yawn too (Figure I.6).

    Male lion yawning.
    Figure I.6 Yawning is not just for humans

    But how does yawning accomplish this cooldown effect? As we suck in air, it moves across the moist mucous membranes of the nasal and oral passageways, cooling the blood in the numerous tiny blood vessels just below the surface. The effect of this is that the blood flow in the head is cooled, and scientists speculate that coolness is transferred to the brain. Have you ever noticed how unsatisfying it is when someone interrupts your yawn? Why do we feel the need to complete it? It turns out the full stretching of the jaw brings blood flow to several muscles too, thus increasing the volume of blood that is cooled due to the radiator effect of the air movement over the nearby mucous membranes.

    The research studies that led to this conclusion involved having participants place warm or cool packs to the head while watching films of people yawning. Scientists observed that participants yawned significantly less with the cool pack on their heads. There are also times during the twenty-four-hour day that people yawn more often, and there are explanations that can be related to brain cooling. Right before bed, body temperature is usually at its highest, which could trigger yawning. Upon awakening, body temperature is quite low but increasing at its fastest rate, prompting a reflex for cooling—morning yawns. However, there are other times during the day when the body increases to or even sustains a higher temperature, so there are clearly complicating factors involved in understanding the complete picture. Months or decades from now, another scientist—perhaps you—will come along and turn this theory upside-down with fresh insight.

    This is one of the satisfying aspects of studying sleep science right now: The frontiers of knowledge are expanding. Today’s genius postulate may be tomorrow’s balderdash. Join me in the wilderness!

    1 Zoë Heller, “Why We Sleep, and Why We Often Can’t,” New Yorker, December 3, 2018,

    Thumbnail: Woman in black shirt Yawning of tired in a black background. (Unsplash License; Debashis RC Biswas via Unsplash

    This page titled Yawning and an Introduction to Sleep is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Sheryl Shook via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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