Katie Wilder-Circadian Rhythm


      This project is on Circadian Rhythms and the effects it has on everyday life. I chose this topic because I thought this was an interesting topic and I wanted to learn more about it. Also, my favorite unit was the states of consciousness unit, which included the topic of Circadian Rhythms. I find it interesting that much of our bodies base their actions on our Circadian Clock. On this page, you will find out how normal Circadian Rhythms function, types of circadian rhythm disorders, popular Circadian Rhythm experiments, the importance of Circadian Rhythm in animals, and the effects Circadian Rhythm has on our health. This information pertains to real life because we all have to sleep, and if we do not get enough of it, our Circadian Rhythms are affected. The following video touches on all 5 subcategories and explains how Circadian Rhythms are part of our everyday life.  

A Normal Circadian Rhythm
      Circadian rhythm is usually about a 24 hour clock that controls the body and its ability to preform certain tasks. A normal circadian rhythm regulates "the timing of periods of sleepiness and wakefulness throughout the day. The circadian rhythm dips and rises at different times of the day, although there is some variation depending on whether you are a morning or evening person. " (1)  Sleepiness is not as strong during these circadian rhythm dips if the person is getting enough sleep. However, if
we don't get enough sleep, our bodies will have more intense urges to get sleep. The circadian rhythm can also help us feel more awake at certain times in the day. Even if you are sleep deprived, you can feel more energetic and awake.

A normal Circadian Rhythm is able to naturally regulate your body and tell it when to wake up, when to go to bed, when to feel alert, and when to eat. All these functions are controlled by the Circadian Rhythm and help you live your daily life. However, if your Circadian Rhythm is off,  numerous disorders that affect the entire sleep and wake cycle may occur. 

The picture on the left (1) describes the average persons body cycle and what functions occur at a given time in the day. For example, at 15:30, or 3:30, a person with a normally functioning Circadian Rhythm will experience its fastest reaction time at this point in the day. 

Circadian Rhythm Disorders

What are they?

Circadian rhythm disorders are disruptions in a person’s natural circadian rhythm that creates continuous disruption of sleep patterns. The disruption results from either a malfunction in the "internal body clock" or a mismatch between the "internal body clock" and the external environment regarding the timing and duration of sleep.

Types of CRDs: 

Delayed Sleep Phase Disorder is a circadian rhythm disorder most common in adolescents and young adults whose "night owl" tendencies delay sleep onset -- often until 2 a.m. or later. If allowed to sleep in late (often as late as 3 p.m.), sleep deprivation does not occur. However, earlier wake up times can lead to daytime sleepiness and impaired work and school performance. These individuals are often perceived as lazy, unmotivated, or poor performers who are chronically tardy for morning obligations. People with delayed sleep phase syndrome are often most alert, productive, and creative late at night.

Advanced Sleep Phase Disorder is usually seen in the elderly. This disorder is identified by regular early evening bedtimes (6 p.m. - 9 p.m.) and early morning awakenings (2 a.m. - 5 a.m.). People with advanced sleep phase syndrome are "morning larks" and typically complain of early morning awakening or insomnia as well as sleepiness in the late afternoon or early evening.

Jet Lag results from a conflict between the pattern of sleep and wakefulness between the internal biological clock and that of a new time zone. Individuals find it hard to adjust and function optimally in the new time zone. Eastward travel is more difficult than westward travel because it is easier to delay sleep than to advance sleep.

Shift Work Disorder affects people who frequently rotate shifts or work at night. work schedules conflicts with the body's natural circadian rhythm and some individuals

 have difficulty adjusting to the change. Shift work disorder is identified by a constant or recurrent pattern of sleep interruption that results in insomnia or excessive sleepiness.

The diagnosis of circadian rhythm disorders is challenging and often requires a consultation with a sleep specialist. Keeping a detailed sleep history and a sleep log for 1 to 2 weeks is essential. It is also important to exclude other sleep and medical disorders, including narcolepsy, which often mimics delayed sleep phase disorder. (2)

The picture featured to the right (2) displays the struggles of Shift Work Disorder and how hard it is to adapt to a radically changing sleep schedule. 

Circadian Rhythm Experiments

    Early research (including some famous experiments in caves) had concluded that the natural "free running” circadian period of human beings was around 25 hours, not the expected 24 hours. However, later research (like that of Charles Czeisler in 1999) showed that these experiments were flawed, and that even the presence of electric lighting was enough to skew the results. It is now clear that, although individual circadian periods do vary - ranging between 23.5 and 24.5 hours in humans, dependent on variations in the person’s PER or period gene - they have a mean of around 24.2 hours, just slightly more than the Earth’s rotation. About 25% of people have a circadian period which is slightly less than the 24-hour day, and 75% have a circadian period slightly more than 24 hours. (7)
Dr. Nathaniel Kleitman sleep experiment

    In a 1938 sleep experiment in Mammoth Cave, pictured on the left, Dr. Nathaniel Kleitman checked on the restiveness of Bruce Richardson. (4)

    In 1952, Kleitman discovered rapid eye movement (REM) – a normal phase of sleep that occurs around four or five times a night, during which vivid dreams occur and lighter sleep is experienced.

    In 1968, two researchers, Allan Rechtschaffen and Anthony Kales, published the first EEG manual of so-called R&K criteria to score sleep stages. They are still used today and consist of four non-REM stages of sleep plus REM sleep. The non-REM stages are divided by monitoring brain waves. Our deepest sleep (AKA slow-wave sleep) consists of stages 3 and 4 of R&K's non-REM stages.

Importance of Circadian Rhythm in Plants

Plants, like other living things, have biological clocks that allow them to respond to changes in time. Among the more obvious clock responses are "sleep movements" - such as the closing of flowers and changes in leaf position that many plants display at night. The growth rate of most plants also differs according to time of the day in a clock-dependent fashion. The circadian clock controls these and other time-dependent responses requires environmental cues to stay synchronized with the 24 hour day. Light and temperature are two of the most important environmental stimuli, since they are two easy signs to differentiate between day and night.

An interesting aspect of the many clock-dependent responses is that they typically persist even in the absence of a daily change in environmental cues. Indeed, the    clock-like rhythms can continue for several days in the absence of external stimuli. However, in most plants the time between peaks (period) of a particular response will drift until the clock is reset by an appropriate external stimulus. The most easily observed circadian responses are leaf movements but other responses can be seen with the right equipment and patience. (3)

This picture, (3) helps describe the Plant Circadian Rhythm and how it impacts plants by showing what happens  to plants as the day progresses. As you can see on the left, the sun and the plant's circadian rhythm plays a big part on the development in plants, without them they would not be able to open their petals, which would lead to bees not being able to pollinate other plants. Without circadian rhythm in plants, they wouldn't be able to sustain themselves and the plants would die. 

Although this picture uses unfamiliar vocabulary, it is still able to get the point across that circadian rhythm and the sun work cohesively together to benefit plants. Without these two factors, sun and circadian rhythm, plants wouldn't pollinate, wouldn't grow, and would affect their health immensely. 

Humans act in a similar way. Our circadian rhythm, along with other outside factors, affects our health greatly. 

Effects on health
    Many factors lead to being unhealthy. One of these factors is how much sleep you get and whether or not your sleep is disrupted. When circadian rhythm is disrupted, sleeping and eating patterns alters and causes numerous health problems. These health problems include an increased chance of cardiovascular problems, obesity, and neurological problems. (4) People who are overweight or obese are more likely to develop sleep apnea, which can interrupt the sleep cycle. This leads to an unfit lifestyle and affects your every day routine.  

    "The researchers believe that [the effects of an altered circadian cycle] may affect how an individual, whether animal or human, responds to additional challenges to the immune or metabolic systems, such as infection ... They are also working on models to understand the impact of different kinds of light-dark shifting such as those experienced by flight crews, shift workers, military personnel and medical residents." (5)

    The circadian rhythms of a healthy person are in tune with the rest of their bodies. Body temperature, for example, starts to rise during the last hours of sleep. This occurs just before waking up. 

Sunlight and other time cues are used to keep your clock set from day to day. This can cause blind people to have problems with their sleep. It is hard for them to get the time cues needed to set their circadian clocks. Other factors (exercise, hormones, medications) may affect the setting of the circadian clock.


    Circadian Rhythm is a widely accepted belief, and not many people criticize it. However, Youngstedt and O’Connor (1999) criticized research on circadian rhythms in athletic performance. These authors maintained that there is no evidence that circadian rhythm in real sports competitions is explained by an endogenous component. They also suggested that the lack of evidence for an endogenous rhythm in physical performance means that sports performance is not affected by either time of day nor circadian rhythm disturbances such as jet lag, when various exogenous factors are taken into account (6). However, this criticism is not widely popular. 

    Circadian Rhythm relies on nature and nurture. Nature affects circadian rhythm because you are biologically predisposed to wake up at similar times as you parents; also, light and the environment controls your circadian rhythm and impacts how you sleep. Nurture affects your circadian rhythm because if you are forced to wake up in the early morning, it becomes a norm for your body and your circadian rhythm adapts. For example, farmers have to wake up early to maintain the farm and collect eggs and milk from the animals. So, farmers wake up earlier because they have been forced to wake up earlier by external factors. 

    The way you sleep is determined through biologic, psychological, and social factors. Circadian Rhythm is affected through biology because circadian rhythm is  determined by serotonin and hormones in the brain that regulate sleep. Circadian Rhythm is affected because of psychological influences if a person has a psychological disorder such as depression, then they sleep more. If they have anxiety, they have trouble sleeping. Circadian rhythm is affected though social influences because if a person stays up late to go to a party, or has to wake up early for something, their circadian rhythm is affected. 

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