Sleep Anatomy: Stages, Rhythms And Effects. Sleep Deprivation And Disorders

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While our sleeping habits have fallen behind in priority as a result of our fast-paced lifestyles, humanity must learn to hold adequate sleep to utmost importance in order to maintain peak physical and mental well-being, and to avoid the disastrous effects of deprivation. As the complexity of the sleep process is often overlooked, appreciating sleep means understanding the intricate biological workings behind it. The need for sleep is controlled by the body’s drive for homeostasis, making it just as important as food, water, respiration, and all other homeostatic activities. As is the case with any homeostatic imbalance, a lack of sufficient sleep can have devastating effects on every part of the body. Nonetheless, people of all ages have been following a trend of decreasing sleep over the years, and the consequences are showing up in numerous ways. There are many reasons for this trend, but the prevalence of sleep disorders is a major issue that calls for more attention. As our society moves into a more nocturnal state, we must adjust our outlook of sleep to recognize that it may be the cause- and vital solution- of many problems facing us today.

Anatomy of Sleep

Circadian Rhythms

To begin with, fully comprehending the importance of sleep involves first gaining a better understanding of what sleep is. We tend to not give much thought to the process of sleeping, and the many complex neurological and biological tasks that it entails. Sleep, or rather the sleep-wake cycle, is controlled by a biological pattern known as a circadian rhythm; this refers to the cycle of bodily processes and changes that take place over the span of twenty-four hours. The sleep-wake cycle is not the only physiological process controlled by an individual’s circadian rhythm: others include body temperate and blood pressure. (OpenStax, 2017, p113) All circadian rhythms are controlled by a specific area of the brain, called the suprachiasmatic nucleus (SCN), which is located in the hypothalamus. The SCN, connected to light-detecting retinal cells that transmit information regarding the cycle of day and night, is what allows the brain to be in sync with the external world and the concept of time. (Colten & Altevogt, 2006, p42-43) The importance of the body’s circadian cycles cannot be overlooked, as these are what allows for an organism to function properly and survive through maintaining homeostasis. (OpenStax, 2017, p113) Despite being regulated by the same rhythm, abnormal sleep patterns are not treated with the same urgency as abnormal body temperate or blood pressure, which can both be causes of immediate medical concern.

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Stages of Sleep

However, circadian rhythm and the sleep-wake cycle are not the only patterns that must be taken into account when discussing the importance of sleep. Sleep itself is a process involving different types and stages, which play different roles in the proper functioning of one’s waking brain. The first type of sleep is non-rapid eye movement (NREM) sleep, which can be further categorized into four distinct stages of brain activity. The first stage of sleep, stage 1, is the process by which your body begins making the transition into the unconscious state when you are first beginning to fall asleep. During these few minutes, your heartbeat and rate of breathing slow, accompanied by a reduction in bodily tension and temperature. Even the brain waves that characterize this stage are those of an individual in tremendous relaxation. (OpenStax, 2017, p121) Stage 2 sleep is relatively similar to stage 1, but waking a person becomes more difficult as the sleeping individual’s condition of relaxation deepens. For the most part, stage 1 and 2 sleep consists of low frequency, high amplitude alpha and theta waves, but studying brain waves in this stage has also revealed the existence of sleep spindles, which are sudden spurts of high-frequency waves. Stage 3 and 4 sleep are called slow wave sleep because of the extremely low frequency and high amplitude delta waves that characterize these two stages, but they can be better described as “deep sleep.” During stage 4 sleep, waking an individual becomes much more difficult of a task. The fifth stage of sleep, in which most dreaming transpires, is known as rapid-eye movement (REM) sleep. In this stage, a person’s eyes will dart around under their eyelids as if they are looking about. In normally-functioning REM sleep, the individual will go into a state of paralysis so as not to move around when dreaming. REM sleep, which has been associated with homeostatic regulation, is believed to be important for memory development, learning, and even emotional processing. (OpenStax, 2017, p124) Despite the stages being listed in numerical order, a person will often shift between different stages throughout the night.

How Sleep Affects the Body

The Brain and Cognition

Although the roles of the different stages of sleep are still being debated among researchers, the overall importance of sleep cannot be overstated. Sleep debt (SD) is the medical term for a chronic lack of sleep, usually in regards to an individual who averages less than 7 to 8 hours of sleep each night. (OpenStax, 2017, 116). Despite being a relatively modern issue, scientists are already beginning to realize the severity of SD consequences. While many researchers argue that a sleep-deprived individual cannot “make up” for a lack of sleep, SD has been shown to be cumulative. (Williams, L., 2017, p27). Acute sleep debt can affect almost every aspect of an individual’s cognition, such as memory, processing speed, and decision making. According to modern brain imaging, it is believed that SD directly impacts the brain’s frontal lobe, which is responsible for most cognitive tasks. (Colten, H., & Altevogt, B., 2006, p142) Perhaps the most noticeable cognitive performance issue affected by sleep debt is the prevalence of spontaneous microsleeps, in which a person remains physically “awake,” but ceases to process information for a brief period of time. (Colten, H., & Altevogt, B., 2006, p138) In other words, they are physically present but not mentally present. Other cognitive deficiencies caused by sleep loss, which often go unnoticed by the sufferers, include lapses in attention span, increased errors in thinking and judgement while under pressure, slower response times, a reduced ability to learn and remember new cognitive tasks, and a general decline in cognitive performance. (Colten, H., & Altevogt, B., 2006, p139-141) Interestingly, the sleep spindles found in stage 2 sleep are thought to be important for the development and retention of memories and learned skills. (OpenStax, 2017, p122).

Other Organs and Organ Health

Furthermore, the brain is not the only organ affected by sleep debt; SD can negatively impact the functioning of many other bodily systems and have acute adverse effects on one’s health. It is common knowledge that obesity is becoming a major epidemic in the modern world, particularly in the United States, but diet and lack of activity are not the only contributing factors: sleep loss has been shown by multiple studies to have a direct correlation with weight gain ands obesity rates. One study found that among 500 adults, those who slept less than 6 hours per night were 7.5 times more likely to be overweight. A study of one-thousand adults revealed a U-curve relationship between sleep and BMI; those who slept too much or too little had high BMIs while individuals who got the proper amount of sleep for the age had the lowest BMIs. Additionally, people who slept too little had increased levels of the appetite-stimulating hormone ghrelin, and decreased levels of the hormone appetite-suppressing hormone leptin. (Colten, H., & Altevogt, B., 2006, p59-60) SD is also associated with increased likelihood of diabetes, brought on by changes in the breakdown of glucose and in the production of leptin and ghrelin. (Maurovich-Horvat, Pollmächer, & Šonka, 2008, p276) Regardless of weight, adults who sleep 5 hours or less have a 2.5 times greater chance of developing type 2 diabetes. The impaired glucose tolerance associated with diabetes can also lead to cardiovascular disease, which may explain why individuals who get 5 hours of sleep or less on a chronic basis show a 45% increase in risk of heart attacks. (Colten, H., & Altevogt, B., 2006, p61-62)

Sleep Deprivation by Age Groups


Nevertheless, age must always be taken into account when it comes to sleep, as sleep patterns and requirements, and the effects of sleep deprivation, change drastically with age. Unsurprisingly, children require the most sleep. From birth to about 3 months of age, infants require 12 to 18 hours of sleep each day. This number gradually lessens as the child ages, and by age 10, he or she only needs about 8 to 10 hours of sleep each night. (OpenStax, 2017, p116) As children grow older, they are more likely to experience difficulties in getting enough sleep than when they were younger. (Colten, H., & Altevogt, B. , 2006, p46) Unfortunately, not much research has been done regarding sleep deprivation prevalence in children, which just goes to show how overlooked the issue is. However, there has been much recent interest in the similarities between attention deficit hyperactivity disorder and the effects of SD in school-aged children. Sleep deprivation has been shown to inhibit parts of the frontal and temporal brain lobes through the neurotransmitter GABA, which can result in “symptoms of inattention, impulsivity, risk-taking behavior, poor concentration, mild cognitive impairment, and generally poor performance.” (Samaan, W.A., 2014, p82) Many children that have been diagnosed with ADHD may simply be suffering from the detrimental effects of chronic sleep deprivation, and could experience symptom alleviation from getting proper sleep.


Meanwhile, contrary to popular belief, adolescents actually require just as much sleep as children in order to function properly (Carskadon, M, 2002, p2). However, studies have shown a worldwide trend of declining sleep times as individuals progress through adolescence. In a 2006 poll of 1602 teenagers in the US, the average weeknight sleep duration of 6th graders was 8.4 hours, while that of 12th graders was only 6.9 hours. According to the poll, sleep duration was higher on weekends across the board, usually because of later waking times. However, this extra sleep not only fails to make up for what is lost, but it may also impact an individual’s circadian clock so that the effects of sleep debt are felt even more strongly on Monday morning. (Kaplan, D, Sass, A, 2010, p409-410) According to the Youth Risk Behavior Study done in 2007, only 7.6% of high school students slept for at least 9 hours on average, while 68.9% got less than 8 hours of sleep per night. (Kaplan, D & Sass, A, 2010, pxii) A major contributing factor of sleep loss in teenagers is the global pattern of delayed sleep onset as adolescents get older. In other words, older teenagers gravitate towards later bedtimes: several studies have shown that while 13-year-olds typically sleep around 10:00 pm on school nights, high school seniors and college freshmen are more likely to fall asleep between 11:00 pm and 2:00 am. (Kaplan, D & Sass, A, 2010, p495) There are many factors that could explain this change, including homework, sports, work, relationships, technology use and technological light exposure, and hormonal time shifts. To further increase the severity of this pattern, high schools often start earlier than elementary schools, with 42% of public high schools beginning before 8:00 am. (Kaplan, D & Sass, A, 2010, p494; National Adolescent and Young Adult Health Information Center, 2014, p1) The sleep deprivation felt by today’s youth is having damaging effects on their academic performance, particularly in university undergraduates. In a study done of 136 adolescents in college, groups that got more sleep each night had significantly higher GPAs than those who got less; 9 to 10 hours of sleep was associated with an average GPA of 3.76, whereas those who slept 3 to 4 hours had an average of 2.91. (Hampton, T, 2005, p31) The phenomenon of more sleep equating to higher grades was also supported by a Finnish study of 5,831 students, in which 3 hours of additional sleep was the difference between an average GPA of 2.74 and 3.24. (Curcio, Ferrara & Gennaro, 2006, p327) The story does not end at worsened academic performance, however. Acute sleep debt in young people also leads to thousands of accidental deaths each year, with unintentional injury being the number one killer of teenagers. 69% of these deaths are caused by motor vehicle accidents. (Kaplan, D & Sass, A, 2010, p500.) Meanwhile, 20% of all car accidents are attributed to driver sleepiness, which impairs a person’s ability to drive in the same ways as alcohol consumption. (Colten, H., & Altevogt, B. , 2006, p148) In one 2013 study of 8 public schools, simply pushing school start times from 7:35 am to 8:55 am resulted in a 70% decrease of teenage motor vehicle accidents. (National Adolescent and Young Adult Health Information Center, 2014, p2) All this shows that adequate sleep could not only help students perform better academically, it could even save their lives.


Likewise, while adults require less sleep than children and adolescents, the importance of sleep and the prevalence of chronic sleep deprivation is no less significant among people over the age of 20. Numerous studies have shown that adults, on average, require 7 to 8 hours of sleep per night to maintain peak mental and physical health and performance. (Williams, L., 2017, p2) Thirty-five years ago, the average adult slept 7.7 hours each night, but recent reports show that nowadays, nearly 1 in 5 adults receive insufficient sleep. This worrying loss of sleep in adults can be primarily attributed to changes in society. Of these changes, the most significant is the new reliance on shift work, which is directly correlated with chronic sleep debt and disturbed circadian rhythms. In modern times, 20% of the workforce works in shifts. In fact, within 10 years alone, the number of people working between midnight and 5:30 am increased by 24%. (Colten, H., & Altevogt, B. , 2006, p57) Sleep deprivation affects adults in the same way as it affects youth, but in the case of said adults, the effects of sleep deprivation manifest themselves most disastrously in work-related accidents and injuries. A longitudinal study done on 50,000 working Swedish adults revealed that those who experienced sleep disturbances were nearly twice as likely to die on the job. In another study done in the Netherlands, workers experiencing extreme fatigue- a common effect of sleep debt- had a 70% higher likelihood of being involved in a work-related accident than their coworkers. (Colten, H., & Altevogt, B. , 2006, p149-150) Additionally, sleep loss, usually resulting from shift work and long working hours, is often felt most strongly by medical workers. According to the Institute of Medicine, fatigue in hospital workers contributes greatly to medical errors, which result in nearly 98,000 deaths per year in the United States alone. (Colten, H., & Altevogt, B. , 2006, p144) In fact, worker fatigue is such a significant threat to public health that many well-known workplace accidents, such as the Chernobyl and Three Mile Island nuclear disasters and the Bhopal disaster in Inda, have been partially attributed to sleep-deprived workers. (Colten, H., & Altevogt, B. , 2006, p138) No amount of safety regulations can prevent the threat to public and individual safety caused by the increase in adult sleep deprivation.

Sleep Disorders

While school, work, and changes in society contribute heavily, another primary cause of sleep deprivation across the board is sleep disorders. In fact, sleep disorders are so prevalent that between 30% and 50% of the population will experience some type of sleep disorder in their lifetime, depending on the population being studied. (OpenStax, 2017, p126) There are many different kinds of sleep disorders, but they can be classified into three distinct categories: insomnia, hypersomnia, and parasomnia. (Wilson & Nutt, 2008, p17) Insomnia is characterized by a lack of sleep, difficulty falling asleep, and low quality sleep that fails to leave an individual feeling refreshed. The most prevalent type of sleep disorder, it is a major public health problem that affects 10-15% of the population. (Wilson & Nutt, 2008, p29) The percentage of people that experience insomnia-like symptoms is actually larger, as a sufferer must experience these symptoms at least three times a week for a month in order to be considered an insomniac. Aside from lying in bed for long periods of time before finally falling asleep, individuals with insomnia may also frequently wake up during the night and then struggle to fall asleep again. Often, this pattern of sleep difficulty is a self-perpetuating cycle, as insomniacs may become anxious about not being able to fall asleep, which further prevents sleep from occurring. (OpenStax, 2017, p126) Hypersomnia, which is defined as excessive daytime sleepiness for several days each week, affects 16% of the population, with another 37% reporting these symptoms for a few days each month. The third category of sleep disorders is parasomnias. (Wilson & Nutt, 2008, p39) There is a large variety of disorders listed as parasomnias, but they are all categorized by the same thing: unusual and disruptive motor activity, behavior, and experiences during sleep. (OpenStax, 2017, p126) Among such disorders are sleepwalking, night terrors and nightmares, and sleep paralysis. Parasomnias can not only disturb the individual with the disorder, they can also result in acute sleep loss for parents and spouses. (Wilson & Nutt, 2008, p51-60)

Tips and Techniques for Better Sleep

However, despite the widespread harmful effects of sleep deprivation, and the prevalence of sleep loss and sleep disorders, the outlook on sleep in modern society is far from hopeless; there are many steps an individual can take to improve his or her own sleeping habits. First and foremost, sleeping and waking around the same time each day, including weekends, allows one to maintain a steady circadian rhythm. This, in turn, is key to maintaining homeostasis. Additionally, it is best to avoid or limit stimulants, such as caffeine and nicotine; it can take up to eight hours for the effects to wear off. In fact, alcohol, which has sedative depressant properties, should also be avoided before bed. Although it can help someone fall asleep faster, it can also prevent them from moving into the deeper stages of sleep. Moreover, exercise can both encourage and prevent healthy sleeping patterns. At least 30 minutes of exercise each day is recommended for proper energy expenditure, but exercising within two or three hours before bed can make it difficult to fall asleep. Likewise, naps should also be avoided in the late afternoon. Relaxation rituals, such as reading or taking a hot bath, can prove incredibly beneficial, as these activities can calm the mind and prepare one’s body for the first stages of sleep. An individual’s sleep environment may be one of the most influential factors in sleep quality. Although some people prefer to have some kind of light on when sleeping, a cool, dark, quiet, and comfortable atmosphere free of sudden noises is ideal. (U.S. Department of Health and Human Services, 2006, p4) Proper bright light exposure and dark exposure are significantly important for maintaining healthy sleeping patterns, as light exposure controls melatonin production and an individual’s biological clock. (OpenStax, 2017, p115) These simple tips can be followed by anyone to improve the quality and quantity of their sleep, but are particularly beneficial in combating sleep deprivation in students and shift workers, as well as alleviating some symptoms of certain sleep disorders.


In conclusion, sleep is a complex bodily function that influences every aspect of an individual’s capabilities and health, and must be prioritized as so. Although sleep has been a topic of interest for centuries, and scientists have made so many recent advances in the study of sleep, our understanding of its purpose is still limited. After all, sleep is a complicated process, not just a period of unconsciousness. However, it is clear that adequate sleep is necessary for reaching the full potential of one’s cognitive abilities, such as reasoning, memory development, and emotional control. Furthermore, with sleep being a primary part of a body’s circadian rhythm, no organ can function properly without it; healthy amounts of sleep can even aid in combatting obesity and illness. People of all ages are missing out on the benefits of being well-rested. In fact, the modern issue of chronic sleep deprivation, caused in part by sleep disorders but also by societal changes, is now manifesting itself in every way imaginable. Nonetheless, there are many easy steps that can be taken to practice healthy sleeping habits and patterns. As the global society moves into a new era of technological and medical advancements, the importance of sleep should not be forgotten. Instead, the only way our society can transition smoothly through this time of change is by accepting and benefitting from the primal clock that drives our every bodily function.

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