Circadian Rhythm and Sleep: Structure, Function, and More

Tara Youngblood Jul 22, 2022

Circadian Rhythm and your sleep

You can’t see it, but it’s a 24-hour cycle behind the scenes that controls your sleep patterns. Known as your circadian rhythms, this natural cycle is generally guided by light-darkness and r promotes consistent and quality sleep.

Circadian rhythms are common with almost all living things on the planet. Our bodies are guided by circadian rhythms, including our physiological processes and behavioral patterns [1].

This is true for mammals, plants, and even microbes. The idea of natural internal rhythms connecting to the cosmos, including the spin of the earth, has long existed in ancient Eastern and Native American traditions.

In the 1700s, French scientist Jean-Jacques d’Ortous De Mairan noted that leaves of certain plants opened and closed with cycles of day and night.[1, 2]

Virtually all life forms…flies, fish, mice, and humans…exhibit circadian rhythms. (p. 86) [3]

What are Circadian Rhythms?

The term circadian rhythm derives from the Latin, ‘circa,’ and ‘diem,’ which translates to, ‘about a day.’ It was first coined by scientist Franz Halberg in the 1950s. This marked the beginning of the growing field of research called chronobiology.

For mammals, circadian rhythms are responsible for controlling numerous physiological processes over a 24-hour period, including feeding, hormone production, body temperature, and sleep-wake cycles.[4]

How Does Circadian Rhythm Work?

Several components make up your body’s circadian rhythm.

Your Internal Master Clock

The Master Clock coordinates all our other biological clocks. The sleep/wake cycle is regulated by the suprachiasmatic (SCN) nucleus, a cluster of about 20,000 nerve cells located in the hypothalamus of the brain. [5]

Its function is to regulate circadian rhythms throughout the body. The SCN receives cues from external environmental stimuli that tell it when to prepare the body for sleep and wakefulness.[6]

These environmental stimuli are called “zeitgebers,” which translates from the German to “time-givers.” Zeitgeber is primarily light, and darkness [7,8], but zeitgebers are also:

  • Physical activity
  • Food intake
  • Temperature [9,10,11]

Additional research confirms that other factors play in the sleep/wake cycle in addition to external environmental cues.[12] Even De Mairan realized this in the 1700s as he studied plants, noting that their leaves open and close per the 24-hour cycle even when they are placed in total darkness.[13]

This finding extends to research on humans as well. Chronobiologists have learned that specialized genes regulate certain circadian rhythms. The period and cryptochrome genes code for selected proteins that promote wakefulness and sleep. [14]

Melatonin and Cortisol

The activity of the SCN sets off an incredible chain of physiological processes. For example, when it receives information from the visual system that darkness is approaching, it stimulates the pineal gland to release the sleep hormone melatonin.

It also suppresses the production of cortisol, a stress hormone. The increase in melatonin, paired with the decrease in cortisol, prepares the body for sleep. As sunlight approaches, the opposite occurs.

The visual system cues the SCN to stimulate the production of cortisol, which promotes wakefulness, and melatonin begins to decrease.

Sleep body temperature

Body Temperature

In addition to hormonal changes, the SCN also regulates circadian rhythm changes in body temperature.[15] As evening approaches, our body temperature tends to drop between one and two degrees, with the lowest temperature occurring approximately two hours before awakening.

Interestingly, during REM sleep (Rapid Eye Movement), the brain temporarily stops regulating body temperature. Thus, we are more sensitive to heat and cold.

The Different Types of Sleep Stages

The Different Types of Sleep Stages

Sleep is an important function for our body to repair. Learn more about the sleep stage, including REM, and how each plays a unique role in maintaining brain health and performance.

The Role of Serotonin in Circadian Rhythms

We often think of the neurotransmitter serotonin in relation to mood disorders, such as depression. Research indicates that it also plays a major role in the function of circadian rhythms. Serotonin serves as a critical link between the basal forebrain and the visual system to the SCN. [17]

Without serotonin then, the SCN doesn’t receive those important messages about changes in light and darkness. This puts the carefully choreographed circadian system into disarray, severely impairing melatonin and cortisol production.

What Changes Your Circadian Rhythm?

So now we know much more about human circadian rhythms' complex and absolutely amazing mechanisms. However, for numerous reasons, these elaborate systems are thrown out of balance at times. Just a few causes might be:

Any of the above can turn the natural sleep/wake cycle on its head. Decreased alertness, daytime grogginess, and irritability are important indications that you're getting shorted on sleep.

Present-day life, with its demands at work and at home, is making it exceedingly difficult to pay proper attention to sleep needs. People sleep approximately 20% less than they did 100 years ago.

A Consumer Reports survey revealed that 164 million American adults struggle with sleep at least once per week. Many of us have trouble waking up in the morning and are restless during the night when we are supposed to be getting consistent and restorative sleep.

Happy couple

Ways to Reset Your Circadian Rhythm

Have you ever wondered why some people don’t need an alarm clock to wake up in the morning? Their bodies are likely syncing just about right with their circadian rhythm. They wake in the morning with natural sunlight and begin to tire as the sun goes down.[18]

Individuals may experience disruptions to their circadian rhythm, but they shouldn’t worry too much. There are ways to get it back on track. Give some a try and see which works best for you:

  • Avoid long naps in the late afternoon or early evening.
  • If possible, refrain from the following in the evening; nicotine, caffeine, and alcohol.
  • Try to stick to a routine each day.
  • Turn off technology leading up to bedtime. (blue light specifically) Try other activities, including reading a book.

Along with the above recommendations, the following sleep tips can help normalize your circadian rhythm:

  1. Explore options for relaxation, such as yoga, meditation, and deep breathing.
  2. Consider a sleep tracker or sleep app.
  3. Redesign the sleep environment, including adding a cooling mattress pad.
  4. Learn about food and drinks that promote sleep.

The more we are true to our natural circadian rhythm, the better our quality of sleep will be.

Dock Pro Sleep System

Dock Pro Sleep System

Did you know the Dock Pro Sleep System offers a “Warm Awake” mode? Select this option to remove the jarring alarm clock sounds with gentle warming that triggers your body’s natural wake response.

Fast Fact Review

New insights into sleep research and chronobiology will undoubtedly continue. Our knowledge of sleep and the complex world of circadian rhythms is greatly expanded. Here are a few important facts to remember about human circadian rhythms:

  1. They are regulated by the suprachiasmatic nucleus, located in the brain’s hypothalamus.
  2. The sleep hormone melatonin promotes sleep, whereas cortisol facilitates wakefulness.
  3. Circadian rhythms are guided by both external environmental cues and internal neurochemical and genetic functions.

Contact a physician if you think your sleep issues might be related to a medical illness or if your sleep quality is not improving.

Citations

[1] National Institute of General Medicine Sciences. (n.d.) Circadian Rhythms. View Resource

[2] Farhud, D., Aryan, Z. (2018). Circadian rhythm, lifestyle, and health: A narrative review. Iranian journal of public health, 47(8),1068–1076. View Study

[3] Ibid.

[4] Vitaterna, M. H., Takahashi, J. S., & Turek, F. W. (2001). Overview of circadian rhythms. Alcohol research & health : the journal of the National Institute on Alcohol Abuse and Alcoholism, 25(2), 85–93. [p. 86]. View Study

[5] Harfmann, B. D., Schroder, E. A., & Esser, K. A. (2015). Circadian rhythms, the molecular clock, and skeletal muscle. Journal of biological rhythms, 30(2), 84–94. View Study

[6] National Institute of General Medicine Sciences. (n.d.) Circadian Rhythms Circadian rhythms are physical, mental, and behavioral changes that follow a 24-hour cycle. View Resource

[7] Suni, E. (2022, April 8) Circadian Rhythm: What it is, what shapes it, and why it’s fundamental to getting quality sleep. Sleep Foundation. View Resource

[8] Harfmann, B. D., Schroder, E. A., & Esser, K. A. (2015). Circadian rhythms, the molecular clock, and skeletal muscle. Journal of biological rhythms, 30(2), 84–94. View Study

[9] Vitaterna, M. H., Takahashi, J. S., & Turek, F. W. (2001). Overview of circadian rhythms. Alcohol research & health : the journal of the National Institute on Alcohol Abuse and Alcoholism, 25(2), 85–93. View Study

[10] Ibid.

[11] Pacheco, D. (2022, March 11). Can you change your circadian rhythm? The Sleep Foundation. View Resource

[12] Suni, E. (2022, April 8) Circadian Rhythm: What it is, what shapes it, and why it’s fundamental to getting quality sleep. Sleep Foundation. View Resource

[13] (Author) (2015, November 9). What makes you tick? Oxford Sparks. [Video]. View Resource,

[14] Vitaterna, M. H., Takahashi, J. S., & Turek, F. W. (2001). Overview of circadian rhythms. Alcohol research & health : the journal of the National Institute on Alcohol Abuse and Alcoholism, 25(2), 85–93. View Study

[15] National Institute of General Medicine Sciences. (n.d.) Circadian Rhythms. View Resource

[16] Morf, J., & Schibler, U. (2013). Body temperature cycles: gatekeepers of circadian clocks. Cell cycle (Georgetown, Tex.), 12(4), 539–540. View Study

[17] Swiner,C. (2020, May 29). What happens when you sleep? WebMD. View Resource

[18] (Author). (n.d.) Serotonin Neurotransmitter. View Resource

[19] (Author) (2020, December 3). Understanding Circadian Rhythms. National Sleep Foundation. View Resource

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