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Circadian rhythm and sleep

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Your Body's Internal Clock and How It Affects Your Overall Health - The Atlantic

      • Not getting enough sleep leaves us tired during the day. But the body's clock also affects mood, mental alertness, hunger, and heart function.

        We all feel the ebb and flow of daily life, the daily rhythms that shape our days.

        The most basic daily rhythm we live by is the sleep-wake cycle, which (for most) is related to the cycle of the sun.
        The most obvious daily process that comes to mind when considering circadian rhythm is our sleep cycle. Though our wills as humans are strong enough to fight our immediate need for sleep (to a point), eventually sleep ends up taking over. The hormone melatonin is involved with helping to signal sleep within an individual. The eyes transmit light information to the suprachiasmatic nucleus; less or no light signals the release of melatonin, telling the body to sleep, vice versa (Pastorino & Doyle-Portillo, 139). Other processes are tied in with circadian rhythm including body temperature.

        It makes us feel sleepy as the evening hours wear on, and wakeful as the day begins. Sleep-wake and other daily patterns are part of our circadian rhythms, (circum means "around" and dies, "day") which are governed by the body's internal or biological clock, housed deep within the brain.

        But research has been finding that the body's clock is responsible for more than just sleep and wakefulness.

        Other systems, like hunger, mental alertness, and mood, stress, heart function, and immunity also operate on a daily rhythm.
        Circadian rhythms are biological cycles lasting 24hours like the sleep/wake cycle, which is facilitated by time-checks and regular events such as mealtimes (external cues). The main internal biological clock (circadian rhythm) in mammals appears to be located in the hypothalamus, which is responsible for “motivation” and is named the suprachiasmatic nucleus (SCN). The SCN has an inbuilt circadian firing pattern as when this has been damaged in rats, the circadian rhythm involving sleeping and feeding patterns has also been disrupted (Zucker et al). The SCN regulates the secretion of melatonin in the pineal gland (another endogenous pacemaker which produces melatonin which affects sleep) and is also connected to the retina of the eye through a separate pathway. This highlights the indirect link between exogenous zeitgebers such as light and how melatonin production from the pineal gland (endogenous pacemakers) works together with the SCN to maintain the circadian rhythm. Light can also reach the brain via other means as Campbell et al demonstrated how it was possible to reset the circadian rhythm through shining light on participants knees. This shows other secondary oscillators exist throughout the body maintaining circadian rhythms through the use of exogenous zeitgebers.

        The existence of the biological clock can be particularly apparent when it's off kilter: Jet lag and shift work can throw our normal patterns out of whack and take a toll on physical and mental health.

        Even shifting the clock an hour forward or backward when daylight savings time begins or ends can disrupt our biological clocks.
        Circadian rhythm describes our body’s natural tendencies to cycle through physiological processes at some regular time interval. A group of brain cells in the hypothalamus play the role of internal biological clocks in keeping humans to the circadian rhythm and are called the suprachiasmatic nucleus (Pastorino & Doyle-Portillo, 139). Remember from a previous chapter that the hypothalamus maintains homeostasis in the body. Also, the hypothalamus controls the pituitary gland. As part of the brain, the hypothalamus is able to cooperate with the suprachiasmatic nucleus in brain to signal other parts in the brain as well as organs and systems throughout the body (via hormones) to turn on or turn off, work faster or slower, in order to stick to circadian rhythm (as much as possible).


          Disrupting our body's natural cycles can cause problems.

      Studies have found there are more frequent traffic accidents and workplace injuries when we spring forward and lose an hour of sleep.
      Aschoff and Weaver placed participants in a bunker without any external cues and found participants to have circadian rhythms between 24-25 hours though some were as high as 29 hours. This demonstrated the existence of circadian rhythms and their endogenous pacemakers (internal clocks), which persisted even without exogenous zeitgebers to influence them. This also highlighted the importance of external cues as these internal clocks were not accurate without them. Due to the lab setting this may have low ecological as it is not indicative of real world settings for sleep behaviour. Also low external validity as this may have then affected the quality or quantity of sleep participants had due to the artificial setup. The sample was also small meaning generalization is more difficult to the wider population where differences may be more evident on a bigger scale. The participants were also volunteers who were aware of being monitored on sleep patterns, which may have caused demand characteristics and affected sleep patterns resulting in results which lack validity and not measuring what the study was meant to measure effectively.

      Heart patients are at greater risk for myocardial infarction in the week following the Daylight Savings time shift. But even more significant is that science continues to discover important connections between a disrupted clock and chronic health issues, from diabetes to heart disease to cognitive decline.
      The textbook notes that teenagers require 8-10 hours of sleep every night (137). At least in my experience, when I was a teenager, sleep was a commodity. In general, between school, homework, sports, extra curricular activities, family time, and time with friends, 8 hours of sleep can be very difficult to maintain.

      It turns out that the same genes and biological factors that govern our internal clock are also involved in how other body systems operate -- and break down. It can be hard to determine whether a disrupted clock leads to health problems, or whether it's the other way around.

      Core body temperature is another circadian rhythm which sees its lowest point at 4:30am (36 degrees) and highest at around 6pm (38 degrees). A slight trough occurs after lunch and this dip occurs even when people do not eat.

      We're beginning to understand more about how the clock interacts with and helps govern the function of other systems and affects our overall health. In fact, keeping your body's daily cycle on an even keel may be one of the best things you can do for your overall health.

      Now in regards to the sleep-wake cycle of our biological clocks, individuals after puberty tend to prefer to stay up later because of changes in melatonin secretions (139). I think that with teenagers demanding more and more freedoms, it is up to the parents to help keep their teenagers in check as to how much sleep they can realistically get a night. Not enough sleep will tend to affect a teenager's behavior in and out of the classroom, possibly leading to poorer grades, a feeling of exhaustion, and possibly even car accidents.


      The idea of a biological clock may sound like a quaint metaphor, but there is actually a very distinct brain region that is charged with keeping time: It is an area called the suprachiasmatic nucleus (or SCN), situated right above the point in the brain where the optic nerve fibers cross.

      This location enables the SCN to receive the cues it needs from light in the environment to help it keep time.
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      But genes also influence the body's clock and circadian rhythms. The system requires both types of input -- light and genes -- to keep it on track. To stay on the 24-hour cycle, the brain needs the input of sunlight through the eyes to reset itself each day.

      I use to be a paraprofessional for an elementary age visually impaired student and we struggled with this issue. There were many times she would come to class extremely tired having not slept well the night before. Like the woman in your link it seemed as though there was a pattern to it. It would have been more helpful if the parents had been more diligent to keep her on a more structured sleeping schedule.

      When humans are allowed to run off their body's clock apart from input from the sun, by being kept in continuous darkness, the body's daily cycle tends to lengthen to about 25 hours. And when people or animals lack the genes that help control the clock's cycle, their sleep-wake cycles can stray even further, or be absent completely.
      That was a very interesting inquisition regarding the blind, I was also thinking how the Circadian rhythm would be affected for people living in places with very long days/nights. Melatonin is a subconscious trigger, but in special cases maybe people try to trigger sleep more consciously, or because the body simply realizes it needs sleep irrespective of light intensity.

      The need for both kinds of cues -- light and genes -- make the biological clock a classic example of how genes and the environment work in tandem to keep the system functioning well.

      Our Behaviors and Body Functions Run on Cycle

      Melatonin is one hormone responsible for our body's daily cycle.

      When night falls and there is less light input to the SCN, the production of melatonin, the hormone responsible for making us feel sleepy, goes up. When it's dark, more melatonin is secreted, which signals the brain to go into sleep mode.
      I was curious about how blind people get around this, since many blind individuals cannot translate light energy entering their eyes into brain signals for vision processing. One article notes that a disorder called non-24 hour sleep-wake disorder affects an estimated 50,000 to 100,000 blind individuals in the United States.

      When the sun rises, melatonin secretion is inhibited, and the brain's awake circuits resume.

      Other systems also follow a daily rhythm, many of which are controlled by hormones and other compounds that receive cues from the biological clock.

      For example, the hormones responsible for hunger and metabolism rise and fall over the course of the day. The chemicals involved in immune system function also vary. Compounds that encourage the inflammatory response rise at night, (which is why fevers tend to spike then), and those that inhibit it rise during the day.

      This is likely because the body is better at fighting infection while it is at rest, and energy can be poured into the effort, rather than into other functions.

      And activity of the stress response system -- particularly in secretion of the stress hormone, cortisol -- is reduced during the nighttime hours, and heightened in the early morning.

      Although there are certain areas of the body, like the heart, that are able to govern their own function to some degree, there is strong evidence that the body clock plays a major role in controlling many of these fluctuations (such as in blood sugar) over the 24-hour period.


      Some of the best knowledge we have about the roles the biological clock plays in our health come from instances in which the cycle gets out of sync.

      This can happen for different reasons, and we're just starting to understand them in greater detail. Sometimes we do things ourselves that disrupt our normal rhythms, like flying to a distant time zone. Sometimes it's other factors, (like genes or biology) that play a role.

      Jet Lag

      Flying across the country on the red-eye is a prime example of how we can disrupt our own clocks, and a far more extreme example than the spring forward/fall back ritual in many parts of the U.S.

      When jet lag sets in, we feel disoriented, foggy, and sleepy at the wrong times of day because, after changing time zones, our body clock tells us it's one time and the outside environment tells us it's another.

      In fact, jet lag can be considered one type of circadian rhythm disorder. It can be treated simply be allowing the body to adjust to the new time, although it may take several days for external cues (light) to help the internal clock catch up or fall back with its new cycle.

      Shift Work

      Shift work is another example of how we can get ourselves off-cycle, and this too can develop into a circadian rhythm disorder over the long term.

      People who work the night shift not only have a hard time with their sleep patterns (feeling sleepy at work or experiencing insomnia during the day), but other systems in their bodies can also feel the effects -- and they can be chronic. It's not been clear exactly why this connection exists, but weight gain or metabolic changes may be involved. These phenomena underline how particular behaviors or lifestyles can affect the body's clock, but there are other factors at play, like genetics and body chemistry.


      The interactions of the clock are complex, and their effects on different body systems are intricate, but we're starting to understand more about how the nuts and bolts of the clock work, and affect each system of the body, from our hearts to our moods.

      Since the biological clock is, in fact, a biological entity, things can go wrong with it that may have less to do with lifestyle or the environment, and more to do with the mechanisms of the clock itself.

      For example, there's more to the clock-diabetes link than just turning our sleep cycle around, though sleep can make a difference.

      The same genes that control the receptors for the sleep hormone melatonin are involved in insulin release, which could also play a role in diabetes risk.

      When melatonin receptor genes have mutations that damage the connection between the biological clock and insulin release people have a significantly higher risk of developing diabetes.

      The Rhythms of the Heart

      The heart is one organ that, although it can keep time by itself to some degree, relies on the brain's biological clock for cues.

      For years doctors and researchers have noticed that heart problems like fatal arrhythmias are more likely to occur at certain times of the day, both in the early morning and to a lesser degree, in the evening hours.
      Hormone production also follows a circadian rhythm with cortisol at its lowest around midnight and peaking at 6am. Cortisol plays a role in making us alert and explains why if awaken at 4am we struggle to think clearly. Melatonin and growth hormone also have a circadian rhythm with both peaking at midnight.

      Taking blood pressure medication in the evening seems to improve its effectiveness because it works with the body's circadian rhythms.

      The reason for this has recently become clear: A genetic factor involved in the rhythm of the brain's clock also controls the electrical activity in the heart.

      Mice who are bred to lack this factor -- Kruppel-like factor 15 (KLF15) -- or have too much of it, have many more heart problems than normal mice. Understanding this clock-heart connection could help experts design drugs to reduce the risk of heart problems in people by stabilizing the levels of these compounds.
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      Immunity and Vaccinations

      Most of us have experienced being more susceptible to getting sick when sleep-deprived. The reason for this appears to be that certain chemicals responsible for immune function, like cytokines, wax and wane throughout the day and sleep deprivation deprives us of their best effects. Animals who are given vaccines at specific times of the day, when certain proteins that sense bacterial invaders are highest, have a much stronger immune response, even weeks later. The same is very likely true for humans.

      Body rhythms don't just enhance vaccines' ability to provide immunity; they can affect the body's ability to battle infection on its own.

      When mice were exposed to a bacterial infection, the severity of their infection reflected the time of day they were infected.

      It's not just in the lab that these effects are seen.

      Babies who are given vaccines in the afternoon -- and who sleep more right after -- have better immune responses to the innoculations. It's likely that the same effect is true in adults, since our immune systems fluctuate in similar ways.

      Rhythm and Moods

      Our internal clocks also have a hand in whether we feel up or down emotionally.

      People with mood disorders like depression, bipolar disorder, and seasonal affective disorder (SAD) have altered circadian rhythms. In fact, sleep disturbances, both sleeping too much and too little, are one of the key symptoms of depression and other mood disorders.

      The relationship between body rhythms and mood is an intricate one, and likely has to do with how the brain chemical serotonin fluctuates in relation to the light-dark cycle and throughout the year as the days become longer and shorter.

      Mice bred to have problems with serotonin function also have seriously altered daily rhythms. People's serotonin levels increase during the part of the day when there is more light available.

      The circadian rhythm-mental health connection has also been linked to disease states like Alzheimer's, Parkinson's, and Huntington's, and even autism spectrum disorder.

      Researchers are finding that disrupted daily rhythms can be good predictors for the development of mild cognitive impairment that comes with age, and even for dementia.

      Experiments in fruit flies (which may seem a far cry from humans, but actually serve as excellent models in biological clock studies) show that degeneration in the brain occurs much more rapidly when there are problems in the functioning of a key clock gene, and the lifespans of the flies are significantly shortened.

      Knowing more about how the clock is related to cognitive function and decline could help experts predict -- and perhaps one day prevent -- it from occurring in humans as well.


      Paying attention to the body's natural rhythms is probably more important to our health than we realize.

      It's not just sleep deprivation that affects our well-being, but it's also the alteration of our biological rhythms that can interfere with so many body functions, making us more prone to health problems like infection, mood problems, and even heart disease.

      Why the biological clock becomes disrupted in certain people, or naturally with age, is not completely clear, but some have recently suggested that it could in part have to do with the aging of the eyes.

      Natural changes in the lens and even the development of cataracts let less light into the eye and, therefore, the brain; and this can affect biological rhythms.

      There are many other reasons our bodies' clocks can go out of sync, which probably involve a combination of genetic predisposition and lifestyle choices, such as alcohol consumption.

      Sometimes the clock can get unset -- as with the changes associated with daylight savings time, air travel, or shift work -- and there's only so much we can do until our body and its clock are in equilibrium again.

      But keeping your schedule on track as much as possible is probably the best advice.

      You probably have a pretty good sense of your body's natural rhythms intuitively. Avoid disruptions to your eat-sleep cycles. Practice good sleep hygiene, and stick to a sleep schedule that works well for your body to keep the system in its natural rhythm. Turning in a little earlier, cutting back on caffeine late in the day, and saving that last bit of work for the morning rather than staying late up to finish it, can make a big difference in how your internal clock functions and in how you feel.

      The Lawyer and Gold Star father believes that Americans should look to its oldest documents for guidance.

        In the fall of 1958 Theodore Kaczynski, a brilliant but vulnerable boy of sixteen, entered Harvard College.

      There he encountered a prevailing intellectual atmosphere of anti-technological despair. There, also, he was deceived into subjecting himself to a series of purposely brutalizing psychological experiments—experiments that may have confirmed his still-forming belief in the evil of science.
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      Was the Unabomber born at Harvard? A look inside the files

      Like many Harvard alumni, I sometimes wander the neighborhood when I return to Cambridge, reminiscing about the old days and musing on how different my life has been from what I hoped and expected then.

      On a trip there last fall I found myself a few blocks north of Harvard Yard, on Divinity Avenue. Near the end of this dead-end street sits the Peabody Museum—a giant Victorian structure attached to the Botanical Museum, where my mother had taken me as a young boy, in 1943, to view the spectacular exhibit of glass flowers. These left such a vivid impression that a decade later my recollection of them inspired me, then a senior in high school, to apply to Harvard.

      This time my return was prompted not by nostalgia but by curiosity.

      No. 7 Divinity Avenue is a modern multi-story academic building today, housing the university’s Department of Molecular and Cellular Biology. In 1959 a comfortable old house stood on the site. Known as the Annex, it served as a laboratory in which staff members of the Department of Social Relations conducted research on human subjects. There, from the fall of 1959 through the spring of 1962, Harvard psychologists, led by Henry A. Murray, conducted a disturbing and what would now be seen as ethically indefensible experiment on twenty-two undergraduates. To preserve the anonymity of these student guinea pigs, experimenters referred to individuals by code name only. One of these students, whom they dubbed “Lawful,” was Theodore John Kaczynski, who would one day be known as the Unabomber, and who would later mail or deliver sixteen package bombs to scientists, academicians, and others over seventeen years, killing three people and injuring twenty-three.

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      New Nutrition Study Changes Nothing

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      Why the science of healthy eating appears confusing—but isn’t

      If you’ve ever been on the internet, you’ve noticed that some things are popular, and other things aren’t. The popular ones have something in common. It’s not quality, or importance, or accuracy, but novelty.

      An example of this is Moby-Dick. It’s a timeless novel by an acclaimed writer, and most people haven’t read it. The complete text is free on the internet. You could be reading it right now. But are you? And how many of your Facebook friends shared Moby-Dick today? Probably not more than one or two.

      Obsession with novelty has been called “neophilia.” The term was used as early as 1965 in a story by J.D. Salinger, who was apparently wary of it. But being attracted to novelty doesn’t necessarily mean readers are dumb or attention-deficient. To some degree, novelty-seeking is evolutionarily adaptive and associated with good health.

      More comfortable online than out partying, post-Millennials are safer, physically, than adolescents have ever been. But they’re on the brink of a mental-health crisis.

      One day last summer, around noon, I called Athena, a 13-year-old who lives in Houston, Texas. She answered her phone—she’s had an iPhone since she was 11—sounding as if she’d just woken up. We chatted about her favorite songs and TV shows, and I asked her what she likes to do with her friends. “We go to the mall,” she said. “Do your parents drop you off?,” I asked, recalling my own middle-school days, in the 1980s, when I’d enjoy a few parent-free hours shopping with my friends. “No—I go with my family,” she replied. “We’ll go with my mom and brothers and walk a little behind them. I just have to tell my mom where we’re going. I have to check in every hour or every 30 minutes.”

      Those mall trips are infrequent—about once a month. More often, Athena and her friends spend time together on their phones, unchaperoned. Unlike the teens of my generation, who might have spent an evening tying up the family landline with gossip, they talk on Snapchat, the smartphone app that allows users to send pictures and videos that quickly disappear. They make sure to keep up their Snapstreaks, which show how many days in a row they have Snapchatted with each other. Sometimes they save screenshots of particularly ridiculous pictures of friends. “It’s good blackmail,” Athena said. (Because she’s a minor, I’m not using her real name) She told me she’d spent most of the summer hanging out alone in her room with her phone. That’s just the way her generation is, she said. “We didn’t have a choice to know any life without iPads or iPhones. I think we like our phones more than we like actual people.”

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      The Case for a Millionaire Tax

      • Derek Thompson

      The Trump administration is poised to slash rates for rich Americans. What about going in the exact opposite direction?

      President Donald Trump on Wednesday pitched a dramatic tax overhaul that would be "the biggest ever" tax cut for middle-class Americans. The pitch included few specifics, but if it resembles past blueprints, there is little doubt that it will indeed be a historically massive tax break—just for rich Americans like Donald Trump.

      There are better ideas. One comes, surprisingly, from the chief adviser whom Trump just fired.

      In July, several news outlets reported that Steve Bannon was pushing for a new tax rate for the richest Americans. Strangely, this puts the alt-right ringleader on the same team as Massachusetts liberals, who recently voted 134-55 to put a millionaire tax—a new tax on all income earned over $1 million—on the 2018 ballot.

    • NASA / NOAA / Goddard Rapid Response Team

      Hurricane Irma Just Hit Category 3

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      Forecasters are monitoring the storm as it makes its way across the Atlantic, but it's too early to tell where it might strike.

      As Harvey moves on from southeastern Texas and floodwaters start to recede, meteorologists are tracking another storm brewing in the eastern Atlantic Ocean that they say could potentially approach the United States in the coming weeks.

    • Irma became a Category 3 hurricane late Thursday afternoon, making it the season’s second major hurricane. The hurricane now packs maximum sustained winds of 115 miles per hour, with stronger gusts.

      Irma had already quickly transformed from a tropical storm Wednesday morning into a Category 2 hurricane Thursday afternoon, according to the National Hurricane Center.

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      It exhibits an unusual—but not unprecedented—rate of growth, according to meteorologists.

      Like Harvey and other Atlantic hurricanes, Irma started as a tropical wave off the coast of Africa and began a slow, westward churn across the Atlantic. Irma will spend the next few days traveling toward the eastern Caribbean region. Beyond that, it’s still too early to predict exactly where the hurricane will go, meteorologists say.

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