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Circadian Rhythms and Sleep

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Biology 202
2000 First Web Report
On Serendip

Circadian Rhythms and Sleep

Sabah Quraishi

The word circadian comes from the Latin circa diem meaning about a day, which starts out as a good definition for circadian rhythms. Circadian rhythms do not have to be daily and in fact can happen in multiple periods per day or periods that last longer than days such as circannual rhythms. The most thought of circadian rhythm is sleep but other examples include, body temperature, blood pressure, production of hormones and digestive secretions. These rhythms do not only take place in humans but are present in a wide variety of other organisms, the simplest being cyanobacteria. Circadian rhythms are usually controlled by a combination environmental factors and internal factors. The most common environmental factors are temperature and light.

Circadian rhythms are controlled by a circadian pacemaker, or a biological clock. This "clock" is the section of the brain known as the suprachiasmatic nucleus (SCN). The SCN is a pair of structures that contain about 20, 000 neurons and is located in the hypothalamus above where the optic nerves cross (1). This proximity to the optic nerve explains its reaction to light. Signals from light are received by the SCN taken in by the retina. Circadian rhythms include three different parts, a central oscillator, afferent pathways that carry environmental information to the oscillator, and efferent pathways that communicate the rhythm of the oscillator to the physiology and behavior of the organism (2).

A specific example of circadian rhythms, or in this case circannual, is in birds. When it comes time for birds to migrate south and then, back north they are signaled by circannual rhythms. Both the change in temperature and the change in length of day have some affect along with internal signals in signaling birds to migrate. Aside from this there is also a signal that helps the bird navigate. It had been found that the signal for navigation comes from within on first flight, but then is learned over time as the bird continues to fly the path adjusting to its current environment (11). This shows how a combination of external and internal signals signal a bird to migrate. This is also true of molting in birds.

Cyanobacteria are the simplest known form of life that has circadian rhythms. Using bioluminescent enzymes as markers a gene cluster was found that is involved in the process. This cluster, kaiABC, are proteins that are part of the feedback loop controlling the system (5). KaiC is involved in setting the clock and depending on the absence of presence of it the clock in cyanobacteria can be changed. The circadian clock in cyanobacteria controls photosynthesis, nitrogen fixation, cell division, respiration, amino acid uptake, and carbohydrate synthesis (6).

There is a twenty-four hour cycle in drosopholia, or fruit flies. This cycle is controlled by genes per, tim, and dbt which are part of the clock. Clk, cyc, and cry are also clock related genes. The cycle in the fruit fly usually begins at about noon when per, tim, and mRNA levels rise and continues until dawn when per, and tim peak and then decrease (6). Light is a factor in the timing of the circadian clock in fruit flies and is a part of regulating its behavior.

The most well known circadian rhythm is the human sleep cycle. Sleep is controlled by neurotransmitters, which act on neurons in the brainstem and in the spinal cord (1). Signals produced by the SCN travel to different regions of the brain. It regulates other functions associated with the sleep cycle such as body temperature, hormone secretion, urine production, and changes in blood pressure (1). The sleep/wake cycle in humans is dependent on light and temperature. A change in these could shift or disrupt the cycle. External factors that affect the circadian rhythm are called zeitgebers. These could be anything from an alarm clock to meal times.

There are many health problems associated with a disturbance in the sleep circadian rhythm. These can be temporary or due to a lack in the circadian rhythm in the body. These include Seasonal Affective Disorder (SAD) where the rhythm is disturbed due to the change in length of day, delayed sleep phase syndrome (DSPS) which is caused by a circadian rhythm abnormality causing the sufferers body to want to sleep later than normal (3). More temporary problems include jet lag and problems caused to those working late shifts.

Melatonin is an internal factor affecting the circadian clock. Melatonin is produced by the pineal gland and it has a day/night function. It peaks during darkness and lowers during the day. Melatonin has been shown to shift biological rhythms. There is a correlation with the circadian rhythm so melatonin can be used to shift the rhythm in terms of therapeutic measures. This not only includes human health problems but other cycles such as in sheep to control breeding cycles (7).

Circadian rhythms seem to fit the profile of brain equals behavior when looked at through the human perspective. The brain takes in inputs along with signals it creates to create an output. What is left unexplained can be seen when thinking backwards. Are circadian rhythms controlled by the brain if organisms without brains posses them? Cyanobacteria lack brains but still respond to circadian rhythms. Aside from cyanobacteria it can be said that plants have a circadian clock which controls photosynthesis and flowering. If this is true what part of the rhythm is controlled by the brain. Could it be that the basic function of circadian rhythms lacks the need of a brain, which is used for only higher functions of rhythms? If this is so where do the rhythms come from.

WWW Sources

1) Brain Basics: Understanding Sleep

2) Hormonal and Pharmacological Manipulation of the Circadian Clock: Recent Developments and Future Strategies

3) Your Ticking Clock

4), Circadian Rhythms and You Biological Clock

5) Glowing Cyanobacteria Gives Researchers New Clues to Circadian Rhythms

6) The Molecular Genetics of Circadian Clocks

7) The Miracle of Melatonin: Fact, Fancy and Future

8) Rapid Resetting of the Mammalian Circadian Clock

9) Working Group Report on Problem Sleepiness

10) The Brain, Circadian Rhythms, and Clock Genes

Other Sources

11)Gwinner, "Internal Rhythms in Bird Migration". Scientific American. April, 1986.



Comments made prior to 2007

My 3 year old grandson gets up between 5 - 6 AM in the morning regardless of what time he goes to bed. Any suggestions for resetting his biological body clock ... Judith Cephas, 1 January 2008


Dov Henis's picture

Circadian Rhythm, Origin And Nature

Circadian Rhythm: Genes Are Organisms, Not Molecular Contraptions

A. "Molecular Basis And Regulation Of Circadian Rhythms In Plants"

B. A mechanisms of energy absorption, by which archae genes became and function as active energy packages, i.e. became living organisms:

C. Chromosomes coil more tightly during the day and relax at night.

D. My elsewhere suggestions re the origin of Circadian Rhythm applies neatly in the above two cases. I posit that the mechanism involved in the absorption of energy by the archae genes is the mechanism of phasing of RNA-type olygomers into replicating primal Earth organisms, individual independent genes. This phasing from chemicals to living organisms was the genesis of Earth's biosphere.

Science will comprehend one day that genes are primal and genomes are evolved organisms.

Circadian rhythm is an innate gene-genome characteristic, inborn-brought-about at the energetic conditions during the genesis of genes in the process of phasing from chemical olygomers to replicating life, to living genes which are base life energy packages.

For the archaic genes, parents of all Earth's Life, direct sunlight was the only source of energy, and it was available to them at different times of the day in accordance with their location on Earth...

Dov Henis

Andrew's picture

Defiance against God and Nature

We abolished slavery here in U.S. Why? Maybe because it was inhuman and abusive. Forcing people to stay awake at night is unnatural and abusive as well. We are coercing our bodies to operate against their design. Why do we do this? Greed, MONEY!

Given the fact that we know that keeping people awake at night is an abusive mistreatment of the human body, why do we still do it? What percentage of white-collar workers, work at night vs. blue-collars? So some human beings aren't worth being treated to healthy living conditions? What made them less worthy?

What is enlightenment? What is progress? If humans are still intent on making progress, they will one-day eliminate shift-work and activities that defy natural law to the most extent possible. Will they? Probably not! Anything that hurts the sacred economy is quickly rejected. Thankfully God is going to step in and restore order and toss all the greedy scofflaws off to eternal nonexistence.

Anonymous's picture

who will look after the

who will look after the patients in hospitals and elderly in aged care facilities if no one stays awake? Its not all about greed.

ESEENA's picture







Serendip Visitor's picture

dont shout

dont shout

Serendip Visitor's picture

"GOD SAYS" - lol souls need

"GOD SAYS" - lol
souls need to recharge? - lol again
gg caps

Dumbo Dimbo's picture

"The EASTER BUNNY says..."

I have found that substituting "the Easter Bunny" for the G_word often helps to put things in perspective.

Anonymous's picture

Be realistic.

I'll leave you to tell the next woman that goes into labor in the middle of the night that she will have to wait until morning to have her baby. Which, by the way, is the prevalent statistic.

And the night a burgler or killer breaks into your neighbor's house, you can tell them that police shouldn't be on call during regular sleeping hours. It's only the most likely time for something like that to happen.

Some night shift jobs are necessary, and the people who take them on are to be commended. A loved one close to me works nights at a hospital in ICU, and while it causes them unquestionable issues with sleep and stress, they still keep at and take pride their job because they are helping others.

Malady and injury do not know the difference between night and day.

Anonymous's picture

We need night shift.

I work night shift and there are advantages. Generally it's quiet and you can get more accomplished. Some people that I work with have been doing it for over 20 years and they can't stand working during the day. They prefer not to deal with politics and extra managers micromanaging.
The problem is when a company utilizes night shift and doesn't properly compensate them. I'm not talking about a little increase in pay. They don't to respect these people and be more flexible with them. These people make many sacrifices to work on night shift. Many times, managers don't see their night shift, so they don't forget about the issues and mistreat the night shift by not being flexible with them.
Many companies are greedy, but some are necessary. Who's watching the streets while you sleep? Who's going put out that fire at night? Electricity is still in use at night.

sharon marie's picture

trouble sleeping due to sexual abuse

i was severely sexually abused as a child and have a very difficult time sleeping now. whenever i do happen to fall asleep it is never more than one to one and a half hours of sleep at a time. do you think you can help me. i have children i have to take care of and i am not doing a good enough job at taking care of their daily needs such as cleaning and cooking.

Anonymous's picture

can't sleep anymore

i keep waiting for my father to come in and abuse me some more even though it's been since 1984. the trauma is still there if there is a sound in the house i am wide awake and on guard. if my dogs bark i am also on guard. if there is a crack in the light under the door i am on guard as it might be him coming in to get me. do you think your circadian can help me sleep?

Norm's picture

get used to it

I'm a railroad worker. We're on call 24/7 365. Welcome to the craziness that is on call life. I mitigate it by eating regularly (every two hours), exercising a hour a day, and TRYING to keep a regular sleep pattern. Also, I don't use caffeine, alcohol, or street drugs.
Good luck.
BTW, You'll hear the phone. I live by it. It's a Pavlovian response.

Amy Erickson's picture

being-on call one third of the month for years

Hi, My name is Amy and I am a healthcare worker. I work Monday through Friday approx 8 hrs. a day sometimes more. I am on call 10 out of 30 days a month. I have trouble sleeping and seem to get irritated quite frequently. I get called in to work at all times of the day and night when I am on call. I toss and turn all night when I do sleep. I feel like I cannot go into a deep sleep because I might not hear my phone or pager. Even when I am not on call, I feel as though I am. Every time the phone rings, I think it is work. I am angry that my place of employment does not respect how I feel. I feel like they rule my life. I work approx 2300 hrs. a year, pluse I am on call approx 2444 hrs. This only affects 3 people in my dept. as we are the only ones that are trained to do ultrasounds. What is your opinion? Am I sleep deprived or just to angry to sleep?