Chapter 4 Sleep
What can sleep apnea cause?
Hypertensions is particularly worrisome because it is directly related to risks of other cardiac disorders, such as coronary artery disease, heart attacks, and strokes. In addition to causing hypertension, sleep apnea directly promotes inflammatory pathways that are thought to further contribute to the buildup of plaques that narrow the arteries of the heart and brain. Cardiac arrhythmias, including atrial fibrillation, which is a major risk factor for stroke, can also be promoted by sleep apnea.
Explain how lack of sleep is similar to being impaired while driving.
In many states, driving while sleepy is considered driving while impaired, and people can be fully liable for the consequences. The National Highway Traffic Safety Administration conservatively estimates that sleepiness accounts for 72,000 traffic accidents per year. The CDC, which believe much drowsy driving is underreported, estimates sleep-deprived drivers are responsible for nearly 6000 fatal crashes each year.
QUICK STATS
40% of U.S. adults unintentionally nod off during the day at least once a month.
FIGURE 4.5
Caffeine blocks adenosine in the brain and delays the homeostatic sleep drive.
How does sleep affect our health?
Sleep directly influences our moods, creativity, and ability to learn, and it has an impact on immune function and longevity. College students who sleep enough hours and sleep efficiently have faster reaction times, higher grades, more optimism, and higher energy levels. They suffer less daytime sleepiness, a lower risk of traffic accidents, and fewer mental health complaints.
FIGURE 4.2
Sleep stages and cycles. During one night of sleep, the sleeper typically goes through four to five cycles of NREM sleep (three stages) followed by REM sleep.
Greek's perception of sleep.
Sleep's resemblance to the loss of consciousness at the end of life was portrayed in Greek mythology. Sleep and death were personified by twin brothers Hypnos and Thanatos.
What are the major sleep drives?
One key for understanding both how sleep can be disrupted and how it can be improved is to understand the natural biological sleep drives. There are two major biological sleep drives: the circadian rhythm and the homeostatic sleep drive.
QUESTIONS FOR CRITICAL THINKING AND REFLECTION
Do you ever use a device right before going to sleep? Do you ever wake up at night to check your phone? How could you change your digital behavior to improve your sleep?
FIGURE 4.1
EEG patterns change with each stage of sleep.
How does sleep help with performance?
Finally, sleep is vitally important for intense skills training. Sleep can help consolidate the motor learning required to make new techniques more efficient and automated. For example, getting a night's sleep after learning to press a sequence on the keyboard enhanced study participants' speed and accuracy on the computer. Some studies have shown that there is only one opportunity to take advantage of this. If you do not get enough sleep the first night after learning, getting extra sleep on subsequent nights will not result in skills improvement.
FIGURE 4.3
The circadian clock of a person who wakes up in the morning and sleeps at night.
How do we strengthen the circadian rhythm?
To strengthen the circadian rhythm, it can help to get good light exposure in the morning and throughout the day and to reduce exposure to light at night. The challenge is that, day and night, we are exposed to abundant sources of artificial light, which undermine our reliance on the sun's natural 24-hour cycle. Electronics compound our unnatural light exposure, especially by introducing blue light. We commonly use backlit electronic devices at night, which can affect our sleep, as well as sleep on the following nights. See the box "Digital Devices: Help or Harm for a Good Night's Sleep?
QUICK STATS
The best time to take a nap is between 1:00 and 2:30 pm
Explain how light exposure affects you and your brain.
A light exposure that would cause a morning reset of sleep time would be between 8:00 and 9:00. This exposure would advance your sleep phase, so that you feel like waking up a little earlier the next day. Interestingly, the reversal point at which the effect of light changes the SCN coincides with the time when body temperature is lowest. Another mechanism involving the SCN detects the loss of light at the end of the day. When natural light fades at dusk, an impulse is conveyed via the SCN to the pineal gland in the brain to produce melatonin, which signals to systems that are involved in preparation for sleep. People who are blind often have problems with sleep because they lack the visual light signals that help synchronize circadian rhythms.
What is micro sleep?
A microsleep, or momentary lapse in concentration, can last just a few second. That brief moment, however, is time enough to fatally crash your vehicle. During a microsleep, your brain loses perception of the outside world. You lose sight, your eyelids closing partially or al the way, and you lose control of your motor skills. Most of the time you don't even realize you've had a microsleep.
How does starting school later benefit the country?
A recent RAND Corporation study has estimated that delaying school start times until 8:30 a.m. would create a 9$ billion economic gain for the country, primarily by greater lifetime earnings realized through better school performance-- and by the reduction in car accidents caused by drowsy teens. Despite these gains, logistics and scheduling hurdles, as well as attitudes that mistakenly associate toughness and discipline with sleep duration, have prevented most school districts from implementing later start times. California will become the first state in the country to mandate 8:30 a.m or later high school start times, with the law going into effect July 2022. In our twenties, our circadian rhythms shift away from the night-owl tendency so that we experience earlier sleep and wake times.
What else affects sleep?
Among a number of other sleep-related physiological factors that affect performance are hormones. Growth hormones and testosterone, for example, are released during sleep, and their levels are reduced with sleep loss. When, for purposes of a study, male college students restricted their sleep to only 4 hours and 48 minutes for a week, their daytime testosterone levels decreased 10-15%-the same amount expected after aging 11 more years. The lowest levels occurred at 2:00 p.m. and 10:00 p.m., when it is likely their homeostatic sleep drive increased. Testosterone is important for muscular health, stamina, and energy, so sleep has a significant impact on men's health.
What else does age influence?
Age not only reduces the time spent in restorative sleep, it also diminishes the number, the amplitude, and the intensity of deep-sleep brain waves. Scientists don't yet know if reduced slow-wave sleep is a response to less physical activity and learning, or an indication that the brains of older adults lose the ability to sustain the slow, coordinated brain activity of deep sleep. Reduced or absent slow-wave sleep may also be linked to neurodegeneration. Due to their tendency to awaken more easily, older people should be aware of factors that can disrupt sleep at night.
Explain how our circadian rhythm changes?
Among the most prominent changes with respect to sleep patterns during the life span are circadian rhythm changes. Children need to go to bed quite a bit earlier than adults, and this should be reinforced by adults. Sufficient sleep schedules reduce problems with attention and learning as well as behaviors that occur in sleep-deprived children. During adolescence and young adulthood, there is a change in circadian rhythm, so that teenagers may not feel sleepy until late at night and have a natural drive to sleep longer in the morning. Like children and adults, sufficient sleep provides adolescents with cognitive and emotional benefits--specifically, it can positively affect grades and mood and reduce risk-taking behavior. Both high school and college students show a sleep deficit of 1-3 hours on school nights. Then they sleep much longer and later on weekends. College students tend to go to bed 75 minutes later than high school students. In a large study of college students, almost one-third reported poor sleep. According to the study's criteria, however, almost two-thirds were getting poor sleep-less than 7 hours of sleep per night and more than 30 minutes of time to fall asleep.
Explain circadian rhythm disruptions.
Anyone who has traveled to another time zone is probably familiar with jet lag, which occurs when the internal body clock is set to a different time from that of a new environment. People with jet lag commonly experience difficulty falling asleep and waking up at appropriate times. It can also cause nausea and loss appetite, which is related to the gastrointestinal system's being out of sync with the new time. But jet lag is not the only disrupter of the circadian rhythm. Some people have habits that cause their internal body clocks to be set at a time that is different for the time zone where they live. An example is a person who stays up regularly until 4:00 a.m. and sleeps until noon, a pattern called delayed sleep phase. If this person occasionally has to wake up earlier-say, to attend a morning lecture or appointment -- the switch can be difficult, and the person may feel unwell, just like a person with jet lag will feel dysfunctional.
Explain circadian rhythm variation.
Are you a "night owl" or a "morning lark"? Genetics plays a role. Larks perform better in the morning, but tire earlier in the day and more sensitive to sleep loss. Owls perform better in the evening and handle sleep loss better. But because they don't grow sleepy until later in the evening, and social obligations often come early in the day, the sleep needs of night owls are often difficult to attain. Many of us fall somewhere in between these two types.
Explain what happens to sleep when we age.
As we age, the duration and quality of our sleep decrease. Children are the hardest to rouse. Their increased amount of slow-wave sleep and greater threshold for transitioning from sleep to wakefulness may explain why sleepwalking is more common in children. Sleepwalking happens during slow-wave sleep, when the transition from sleep to wakefulness does not happen easily.
What do sports teams do to help with their sleep schedule?
Because performance can be improved by changing our sleep habits, professional sports teams and athletes have started hiring sleep consultants. One researcher studying competitive college swimmers observed that after adhering to a more rigid sleep schedule, students performed their personal bests. The research was more formally developed to evaluate college basketball players, and it showed that shooting accuracy and sprint times improved after several weeks of instituting a 10-hour sleep schedule.
Explain sleep debt.
Because we consistently underestimate how sleep deprived we are, we risk our own and others' lives without realizing it. One misconception is that we can recover from missed sleep with one or two good nights' rest. But even three nights of recovery sleep does not bring us back to full functioning. How many errors are committed on the road, in the skies, or while controlling hazardous materials because the operator falls asleep? What can we do about this? You can notice a sleep deficit with the following signs: difficulty getting out of bed in the morning and missed alarm clocks, an ability to fall back asleep at 10:00 or 11:00 a.m., an inability to feel alert before noon without caffeine, grogginess that lasts more than a half hour after waking or continues after the natural circadian post-lunch dip, and a tendency to fall asleep while reading or watching a movie. Frequent movement during sleep as recorded by a wearable device can indicate awakenings and fragmented sleep you may not even be aware of and can thus be an indication of sleep debt. While brief naps at certain times of the day can renew alertness, the ability to fall asleep during the day can also be a sign of sleep debt.
What happens to our sleep when we get older?
By our late twenties, we enter less into deep sleep. By our late forties, 60-70% of deep sleep is gone. By age 70, it has decreased 80-90%, and by age 74 it may be completely absent. Still, not all older adults suffer the same degree of sleep disruption. There are, for example, differences among the sexes: women over the age of 70 show much less disruption and impairment in slow-wave sleep than men over 70. As we get older, we wake up more easily. The elderly generally wake up more often during the night because they are in lighter stages of sleep. They have lost a lot of the deep sleep stage and so are more sensitive to external stimuli. The shift to earlier sleep and wake times, combined with sleep debt and reduced deep sleep, can cause inadvertent napping too late in the day, which can in turn prevent sleep when it is attempted at bedtime. Their regressed circadian rhythm prevents catch-up sleep in the morning and leads to more sleepiness during the day.
How does caffeine affect sleep?
Caffeine blocks the homeostatic sleep drive by blocking adenosine receptors in the brain. If you have problems falling asleep, reduction of caffeine can be very important. It is important to bear in mind that caffeine can have effects for up to 24 hours; even if consumed in the morning, it can disrupt nighttime sleep.
QUESTIONS FOR CRITICAL THINKING AND REFLECTION
Can you remember a time when you were sleep deprived and did something you regretted? How did you feel that day?
QUESTIONS FOR CRITICAL THINKING AND REFLECTION
Can you think of a time you had an early class and had difficulty focusing? Did you make adjustments to your schedule? What other actions improved the way you felt?
Explain Stage II of sleep.
Deeper than Stage I but still a light sleep is Stage II. In Stage II sleep, the heart rate slows and body temperature drops. The EEG shows bursts of brain activity called sleep spindles and k-complexes. Lasting one or two seconds, these waves appear only during NREM sleep, and they occur most often in Stage II. These bursts represent the brain working to remain sleep during occurrences of external stimuli, such as a noise in the room. But in this stage of sleep, sensory stimuli from the environment cannot longer reach the higher-level brain centers, meaning people are not as responsive. If awakened, people in Stage II are more likely to know they had been asleep.
How does our mood affect sleep?
Depression and anxiety are common; most people will experience them at some point in their lives. Sleeping difficulty, especially insomnia, is often also present in people struggling with depression or mood disorders. Research shows that the risk for depression rises with insomnia, even when people were not depressed when sleep troubles began. Recent studies have also shown that when patients with depression specifically treat sleep problems, their depression also improves, even if the treatments are not medicinal. One explanation for this link is that the nuerochemical changes associated with sleep problems make people more vulnerable to depression.
What condition may be caused because the lac, of sleep?
Diabetes is also a common condition, and it increases the risk for other disorders, including cardiovascular diseases. According to the Centers for Disease Control and Prevention (CDC), prediabetes is present in over one-third of people aged 18 or older and in nearly half of people 65 or older. Diabetes mellitus is also listed as the seventh most common cause of death in the United States. While obesity is by far the major risk factor for the development of diabetes after childhood, sleep can affect the risk for developing diabetes. In another series of studies in which people were asked about their sleep quality, those who reported problems falling asleep or staying asleep had a 50% increased risk for developing diabetes. When sleep apnea goes untreated, people appear to have problems with glucose regulation also seen in diabetes. In young, healthy people, when slow-wave sleep was disrupted by low-grade noise, even when the total sleep time remained the same, the ability of insulin to regulate glucose was impaired.
Explain how sleep can affect driving?
Do not get behind the wheel without enough sleep. In driving simulations, study participants who slept only four hours a night drove off the road six times more often than people who had slept eight hours. The number of errors committed by the sleep-deprived matched the number committed by another group of participants who had slept eight hours but were legally drunk. A fourth group, both sleep-deprived and drunk, drove off the road almost 30 times more than the rested, sober group. This means that the combination of alcohol and sleep deprivation are exponentially lethal; unfortunately, people tend to drink alcohol at nighttime, when sleep pressure is greatest.
How do we measure sleep?
Even though we are not conscious when we are sleeping, our brains are still active. Sleep is divided into distinct stages characterized by different patterns of electrical brain activity. The way these patterns come together is called sleep architecture, and it changes over the course of the life span. Brain activity during sleep is typically measured by a monitoring device called an electroencephalogram (EEG). During wakefulness, when a person is quietly resting with eyes closed, the EEG shows a pattern called the alpha rhythm This pattern is characterized by regular brain waves that occur 8-10 times per second. These brain waves change, and different parts of the brain are activated or suppressed as a person progresses through the three stages of sleep.
How much sleep should we get every night?
It is important to realize that the requirement for sleep depends on the individual. Genetics plays a role in how much sleep we need. Carriers of specific genes may be so-called short sleepers, who need only 4 to 6 hours of sleep per night to prevent sleep deprivation. Other individuals need 9 or 10 hours of sleep to feel their best. How much sleep we each need is up to each of us to figure out. But the optimal amount of sleep, for most people, should fall within the ranges recommended by sleep research.
How does lack of sleep affect people?
It is probably apparent to most people that a night of poor sleep can make them irritable the next day. This effect can compound over the course of many days or weeks. Lack of sleep can also affect emotions, making people more volatile and disinhibited, which can lead to behaviors people might regret or decisions that are not carefully thought out. In adolescence and young adulthood, risk-taking behaviors have been shown to increase with insufficient sleep.
How does affect the SCN?
Light has a direct connection to the SCN master clock via specific cells in the eye. Instead of processing vision, these cells send impulses directly to the SCN to allow it to measure light. If we are exposed to light in the morning at a certain time on a regular basis, this exposure signlas the SCN that it should set the internal clock to wake around that time. This allows us to develop sleep habits that are naturally regulated. But exposure to light can also reinforce unhealthy behavior. For example, if we are regularly exposed to it late at night, then the SCN will reset itself, shifting our sleep and wake periods to occur later. This is because the body responds to light int he evening by delaying the sleep phase. In contrast, when we are exposed to light in the morning, our body resets to an earlier clock time and earlier wake time, advancing the sleep phase. If your goal is advancing the sleep phase, the early-morning light exposure needs to occur about two hours prior to your usual wake time, and not before. For example, let's say you usually get up at 10:00 am. You stay up late with the light on, and even though a 6:00 a.m. light hit you too early, and you will still not feel like sleeping at an early bedtime.
Do mobile devices actually affect your sleep?
Many apps are promoted as sleep aids and trackers. Can they really improve sleep? Or can using digital devices hurt the body's natural sleep cycles? Before we look at sleep apps, let's consider how your use of digital devices can negatively affect your sleep. Tablets, smartphones, and computers emit blue light, which impeded the release of melatonin, a hormone that affects sleep and wake cycles. In one study, research compared the sleep of people who read an e-book on a backlit digital device in the course before bedtime with that of people who read a print book. Those who read the backlit digital book had reduce melatonin release and therefore took longer to fall asleep and were less alert the next morning. Does heavy texting affect sleep? Psychologist Karla Murdock reported the texting was. direct predictor of sleep problems among first-year students in a study that examined links among interpersonal stress, text-messaging behavior, and three indicators of college students' health: burnout, sleep problems, and emotional well-being. Murdock and other sleep experts suggests turning off your screens. Use them less during the day and also when preparing to sleep at night. If you have trouble relaxing and transitioning to sleep in the evenings, shut down all your devices an hour or more before you intend to sleep.
Explain how digital sleep trackers benefit your sleep.
More complicated technologies try to track and analyze sleep. Many are based on movement detectors inside smartphones. Others work with sensors attached to your mattress or pillow that estimate the amount and type of sleep you get based on your movements during the night. These apps may generate detailed graphs of your sleep quality and may time your wake-up alarm to go off at the point in your sleep cycle when you will feel the most refreshed. Some apps also include a sound recorder, which detects sleep talking, snoring, and other noises, providing further information about nighttime sleep behavior. In addition to smartphone apps, specialized fitness wristbands such as those by Fitbit include sleep trackers. These rely on wearable movement detectors. Some incorporate heart-rate data as well, but evidence is meager that adding heart-rate data to movement data improves the accuracy of results. Certain fitness-focused wearables may combines sleep and exercise data to provide an overall picture of an individual's activity over the course of a day. Apps and devices may be popular, but no current consumer technology can match a sleep lab when it comes to detecting sleep stages or diagnosing specific sleep disorders such as sleep apnea. If you enjoy the features of an app or wearable tracker, go ahead and use them, but don't rely on an app to diagnose the presence or absence of a serious sleep problem. One good effect of using a sleep tracker is simply the greater focus it places on sleep.
What is night in the circadian rest phase?
Night is our circadian rest phase, and though we are physically inactive during sleep, our bodies are repairing cells, removing toxins, and consolidating these life sustaining tasks. Interestingly, not everyone shares the same physiological clock times. The average clock time is about 24 hours.
Can you smart phones help you sleep?
Now that you are resting in the dark, why would you consider using a sleep app or digital tracer? Ironically, a smartphone may help you get to sleep. Many free and low-cost apps provide aids for relaxation and for improving sleep. Some include music, white noise, or nature sounds (e.g., wind, rain, waves, or songbirds). Others offer specific techniques, such as guided meditation or breathing exercises, to promote relaxation to aid in falling asleep. Experiment to find the aids that work best for you.
Explain what Dementia is.
One major disease that can affect memory as we get older is dementia. Dementia is so common that up to 20% of us are likely to develop memory problems as we age. This is a devastating disease, but it turns out that better sleep may help prevent us from developing mild cognitive impairment and dementia. Studies in mice have revealed that there are changes in the fluid that surrounds the Brian during sleep, such that the flow around the nerve cells or the cerebrospinal fluid increases by 90% in the tissues of the brain while we sleep. It appears that this increase in flow allows for by-products of nerve metabolism to clear out. These by-products include proteins such as amyloid, which can accumulate in the brain during the day and have been associated with the development of Alzheimer's disease, a form of dementia. The fluid-clearance system in the Brian, called the lymphatic system, processes the waste from the brain. Without sleep, this system does not clear as efficiently. Epidemiological studies and cohort studies in humans provide further evidence that poor sleep, particularly sleep disruption at night, increases the risk for dementia or causes it to develop earlier.
Who is at risk of accidents form lack of sleep?
People who are most at risk for falling asleep driving are those who regularly get less than seven hours of sleep. They include young people aged 18-29 and men slightly more often than women. Other candidates are parents with small children, shift workers, people who have accumulated sleep debt, or those who have other untreated sleep disorders such as sleep apnea or insomnia. Although they can occur at any time, the peak period for drowsiness-related accidents is 4:00 to 6:00 a.m. Sleepiness can increase when people take substances such as muscle relaxants, antihistamines, cold medicines, or alcohol.
Explain insomnia and sleep.
People who sleep less or who have insomnia also appear to have increased cardiovascular risk. In men with insomnia and sleep duration of less than six hours, there was an increased risk of mortality over 14 years of 400%. If these men also had hypertensions, the risk rose to 700%. A study of more than 6000 people showed that insomnia in midlife led to a threefold greater risk of mortality over 13-15 years. How helpful are sleep medications? Because sleeping pills generally inhibit neural activity and do not produce natural sleep, it is best to avoid them if possible. Several large studies suggest that the use of sleep medications is associated with a higher mortality risk.
How does sleep cause pain?
Poor sleep can increase our risk for developing body pain and create a lower pain threshold. If someone is suffering from body pain, it is especially worthwhile to screen for sleep disorders. Improving a patient's sleep can improve pain symptoms. One challenge to this approach is that pain can interfere with sleep, creating a feedback loop; however, in some patients it may be easier to address sleep problems, which can ease pain symptoms and , in turn, lead to better sleep.
How does school affect sleep routine?
School start times often force students to rise during their biological night--their circadian period scheduled for sleep--and this results in serious sleep deprivation. Sleep is especially important during adolescence because parts of the brain in charge of higher-order thinking, problem solving, reasoning, and good judgement are still developing. School districts that have implemented later star times, allowing teens more sleep and biologically appropriate wake times, found a decrease in tardiness, absences, dropout rates, school nurse visits, and car accidents and improved alertness and behavior in class, better grades, and higher standardized testing scores.
How does sleep affect the body?
Sleep affects almost all systems of the body, including the respiratory, cardiovascular, endocrine, gastrointestinal, urinary, and nervous systems. When we fall asleep, our heart rate and respiratory rates slow, our blood pressure dropsy nd our body temperature declines. Our consciousness is also profoundly changed during sleep. We are less responsive to the surrounding environment, and we experience fantastical dreams.
Explain sleep patterns across the lifespan.
Sleep rhythms and needs change throughout our lives. Babies need the most sleep and may sleep up to 19 hours per day. As you can see from Figure 4.6, the number of sleep hours we need generally declines until adulthood, at which point most people need between 7 and 9 hours of sleep. Teenagers typically need 8-10 hours of sleep nightly, but surveys of adolescents across the world make it clear that most teenagers get much less than the recommended amount. Some teens may try to restore their sleep deficit on the weekends, which can be a regular pattern, but even so, teenagers are often sleep deprived during the week.
How can sleep improve mental health?
Sometimes sleep problems are correlated with suicide risk, especially among young adults. A study of 438 female college students reports an important association between insomnia and suicidal thoughts. Other studies of college students found an association between nightmares and suicidal thoughts. Some students classified as suicidal also reported taking sleep medications and often feeling to cold while sleeping. Being aware of the connections between mood and sleep, and prioritizing sleep health, can contribute to better mental health.
Describe stage 1 of sleep.
Stage I is a short transitional phase from wakefulness to sleep. It is light sleep, easily disturbed by outside stimuli. Sometimes it is hard to differentiate between a person's awake state and Stage I. Someone who wakes from this stage may not even be aware they had fallen asleep. In Stage I, the eyes may move slowly back and forth (not to be confused with rapid eye movement sleep, described below); respiration grows more regular than during wakefulness; and muscles relax and may twitch.
Explain Stage III of sleep.
Stage III is the deepest stage of sleep and the one most necessary for feeling well rested upon waking. It is also believed to be the stage that supports the most restorative function, such as rejuvenating actions like synthesizing proteins or managing stress. The length of this stage increases after physical exercise or extended periods without sleep. In this slow-wave sleep, or deep sleep, it is difficult for us to wake up quickly and, if awakened, we may at first be confused for several minutes. Parts of the brain associated with memory, learning, and other cognitive functions can become active during Stages II and III.
What other factor affects athletes?
The amount of sleep is not the only influential factor: Circadian rhythms also affect performance. A study of 40 years of NFL compared West Coast versus East Coast teams who were playing on the opposite coast. Crossing time zones, especially with longer flights, increases fatigue and jet lag for most athletes. But the real disadvantage hits the East Coast teams playing night games on the West Coast. They consistently performed poorly due to circadian factors that kick in by the game's end, around 2:00 a.m. on their body clocks. Nighttime exercise also disrupts sleep schedules by delaying athletes' sleep onset.
What is the circadian rhythm?
The circadian rhythm is the sleep-and-wake pattern coordinated by the brain's master internal clock, the suprachiasmatic nucleus (SCN). The SCN controls the sleep-wake cycle not only of the brain but also of the entire body. Every cell in the sleep-wake cycle not only of the Brian but also of the entire body. Every cell in every organ has a sleep-wake cycle, DNA machinery that produces an internal clock; and the SCN synchronizes all of them. It also regulates the timing of hundred of other biological processes, including hunger and thirst, sexual behavior, body temperature, and emotions. The power of the circadian system for many different aspects of biology is being increasingly recognized, and the 2017 Nobel Prize in Physiology was awarded to Jeffrey Hall, Michael Rosbash, and Michael Young, scientists who helped explain the genetic mechanisms underlying clock timing on the cellular level.
How can sleep cause cardiovascular disease?
The connection between sleep and cardiovascular disease has been studied extensively. The strongest connection is between sleep apnea, which is prevalent in people who snore, and hypertension (abnormally high blood pressure). One of the largest studies showed that people with mild sleep apnea had twice the risk of developing hypertensions in the next four years, while those with moderate or severe apnea had three times the risk.
Explain what REM sleep is.
The final stage of sleep is rapid eye movement (REM) sleep. REM sleep is named for periods during which the eyes under closed lids move quickly, similar to a person who is awake. This is when most dreaming occurs. Although it can be difficult to wake people from REM sleep, once awake they are usually oriented to their surroundings and not confused. Unlike the synchronized brain waves of NREM sleep, in REM sleep the brain exhibits electrical activity that is indistinguishable from that of a person who is awake and engaged in complex thinking. Some regions of the brain are up to 30% more active during REM sleep than during wakefulness. This is especially evident in parts of the brain that are related to emotions. Blood pressures, respiration, and heart rate also rise in REM. Muscles in the limbs, however, are actively inhibited by the brain so that the body is prevented from moving during dreaming, a form of paralysis.
Explain what NREM sleep is.
The first three stages of sleep are grouped together as non-rapid eye movement (NREM) sleep. The purpose of NREM sleep remains mysterious, but theories suggest that it improves neural connections; it also facilitates information processing and cell restoration and repair. As we move through the stages of sleep, brain waves grow larger and slower. Resting with eyes closed produces an EEG pattern called the alpha rhythm. Stage I and II sleep produce theta waves. In the deepest stage of sleep, Stage III, delta waves are even slower, like large waves in the ocean (see Figure 4.1)
What is the good news due to lack of sleep?
The good news is that accidents due to sleepiness can be prevented. First and foremost, It is important to ensure adequate sleep time and avoid extremes of sleep deprivation and ensure that any disorder of sleep, like sleep apnea, is properly treated. If you feel drowsy while driving, it is best to immediately pull over and stop driving.
How do the sleep drive and the circadian system work together?
The homeostatic sleep drive and the circadian system interact in a complex process of mutual opposition. The pressure to sleep generated by the homeostatic sleep drive is directly related to how much sleep we've gotten and how long we've been awake. The alerting signals generated by the circadian clock, however, are not influenced by time asleep or awake, but instead occur each day at the same time. These two sleep-regulating forces work independently of one another, although they are broadly aligned to promote sleep and wakefulness.
Explain what the homeostatic sleep drive is.
The homeostatic sleep drive is the pressure to sleep that builds in relation to the amount of sleep you've had and your duration of wakefulness. The circadian process works in opposition to the homeostatic drive, instead arousing networks to promote wakefulness. The homeostatic sleep drive is like an hourglass that turns over the moment you wake in the morning: the pressure for sleep builds up steadily throughout the day. If you do not sleep all night, and you stay up the next day, you will feel an ever-increasing need to sleep. The homeostatic sleep drive is thought to be mediated biologically by the accumulation of the neurochemical adenosine in the brain. This is a by-product of energy metabolism in the brain and promotes sleep onset. So the more time one spends awake, the more this by-product accumulates and produces sleepiness. When one falls asleep, this by-product is cleared, and the pressure to sleep is reduced. Naps in the afternoon will clear adenosine and reduce feelings of sleepiness during the day, but they may also reduce the pressure to sleep at night. Different people may have stronger or weaker homeostatic sleep pressure systems. Someone with insomnia, who has a problem falling asleep or staying asleep, might benefit from trying to increase sleep pressure and strengthen the homeostatic sleep drive. This can be done by setting a reasonably early wake time every morning and avoiding naps during the day, allowing enough wake time for the sleep drive to increase.
What can we learn about sleep?
We spend almost one-third of our lives asleep, but few of us understand what sleep is for and why it is necessary for our health. Since we are mostly unconscious during sleep, it is not uncommon to feel that we could be better off if we did not need sleep, and it can be tempting to cut back on sleep to make more time for entertainment or work. As we learn more about how sleep promotes all aspects of our health, however, we see that sleep is as vital as nutrition and physical fitness.
Explain the sleep cycle.
When people fall asleep, they first cycle through the three stages of NREM sleep, possibly repeating Stage II after completing Stage III. This is followed by a period of REM sleep, which is always a final stage in the sleep cycle.. From beginning to end, the sequence lasts about 90 minutes, and then the cycle repeats. During one night of sleep, a person may go through four to five cycles, but the cycles differ somewhat over the course of the night. The periods of slow-wave sleep are longer in the first part of the night, and the periods of REM are longer in the last part of the night; confusional awakening and sleepwalking are therefore more likely to occur during this time. Because people have more REM sleep in the last part of the night, that is when dreaming most often occurs.
What sleep problems do women have?
Women in general report more symptoms of sleeplessness and are more likely to be diagnosed with insomnia; men report more snoring and are more likely to be diagnosed with sleep apnea, repeated involuntary breathing pauses during sleep. One reason women may notice changes in their sleep patterns is hormones. During the menstrual cycle, some women may experience increased sleepiness or disrupted sleep. Progesterone levels rise during the second half of the menstrual cycle, promoting sleep, but drop just before the cycle begins, causing sleep difficulty. During pregnancy, extra weight and the position of the fetus can make sleep difficult. During menopause, many women have additional sleep problems, such as hot flashes. Awareness of these changes in sleep can help women cultivate strategies to ensure that they meet their sleep needs, despite these hormonal influences.
How does sleep affect the workplace?
Workplace accidents and even major environmental disasters have been attributed to human error that was related to sleepiness. Such errors contributed to the 1989 Exxon Valdez oil spill in Alaska, the 1986 Chernobyl nuclear disaster in the Soviet Union, the 1979 Three Mile Island nuclear disaster in the United States, and even the 1986 space shuttle Challenger disaster, each of which was related to sleep deprive workers. The U.S. Navy has reevaluated the schedules of crews to ensure they get enough sleep while at sea. Sleep deprivation is a suspected cause of at least four major incidents in 2017 alone that resulted in the deaths of 17 sailors.
How can you prepare for sleep deprived driving?
You can prepare for anticipated period of sleep deprivation by napping. Studies found that pilots who napped early int he evening before a red-eye flight could protect themselves from lapses in concentration that are so dangerous in the last 90 minutes of the flight. Caffeine can provide a short-term burst of alertness if needed, but it shouldn't be used excessively because it can promote sleep deprivation. Open windows and sufficient noise from a radio for simulation may help. It is always important to remember that only a few seconds of losing consciousness on the road can lead to tragedy, and the best course of action is always to stop driving when drowsy.
