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Questions tagged [circadian-rhythms]

Any biological process which displays an endogenous, entrainable oscillation of time.

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Temperature-dependence of circadian rythms

A circadian rhythm is a chemical clock. In the absence of light or other stimuli to entrain it, its speed depends on reaction rates. As a rule of thumb reaction rates double every 10C as long as the ...
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Does sleep schedule affect circadian rhythm?

During the circadian rhythm, the internal human body temperature supposedly peaks around 4-6 pm. Let us assume that the average person goes to bed around 11 pm and sleeps for 8 hours. In that case ...
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Rationale for two-components in feedback loop of circadian molecular clock

The circadian clock in humans and fruit flies involves a feedback loop in which the active components are protein heterodimers. This is illustrated for humans in the diagram below: The nuclear ...
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Why are fearful stimuli more powerful at night?

For example, horror movies appear to be scarier when viewed at night than during broad day light. Does light have any role in this phenomenon? Are there changes in hormones at night versus during ...
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Which genes/proteins constitute the core components of the circadian clock?

What the title says. For instance in Drosophila melanogaster and Mus musculus (see Patke et al. 2020) the CLOCK, CYCLE/BMAL, CRYPTOCHROME, PERIOD setup seems to be conserved. But other components also ...
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Blooming at moonlight

At the moment a popular question in the physics SE community is about night-blooming cereus: this flower blooms at full moon, that is it is capable of making difference between the moonlight and ...
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Why do morning people have shorter biological clocks?

First of all, we all have a circadian clock than is run endogenously by differential gene expression and controls our change in awakeness, temperature, hormone levels, etc.. Circadian clocks are not ...
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How do people wake up just before their alarm goes off?

I can wake up less than 2 minutes before my alarm goes off regularly. I read the common wisdom on the subject which says "circadian rhythm; PER proteins; internal clock". I am skeptical of ...
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Do circadian hormones fluctuations follow sleeping patterns or the time of day?

It is said that testosterone and cortisol are at their highest early in the morning, at 8 am, and lowest at night. What happens, though, if someone regularly goes to sleep at 8 am and wakes up in the ...
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Sleep deprivation relation to growth rate and mental health in adolescence

Do sleep deprivation and its timing affect growth rate and mental health in adolescents? If so how much sleep is enough for teenagers?
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Circadian rhythm in birds

Animals can use their circadian clocks to determine direction from the position of the sun. In a particular experiment conducted in Iceland, a bird, kept in a cage open to the sky, was trained to ...
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A biological system to measure time

First of all I am a physicist, so I apologise for my non-existent understanding of basic biology. However, I have what I think is an interesting question and this seems like a good place to ask it... ...
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Is there benefit of use of red light over dim white light when interacting with rodents in the dark phase?

I've come across some "percieved wisdom" that rats and mice do not "see" red visible light and so use of this wavelength will allow humans to interact with rats in their active nocturnal phase without ...
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What is the connection between sleep requirement and age?

By this question: Is the human biological clock genetically programmed or learnt? we discussed that the sleep requirement depends on the age of the individual. - Figure 1. - Sleep requirements by age ...
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Circadian clocks in enzymes

I'm aware of the existence of circadian clocks, but I don't understand exactly how circadian clocks regulate other circadian mechanisms. For example, if an enzyme is found to have a circadian rythm, ...
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Why aren't circadian rhythms exactly 24 hours long?

Most organisms exhibit circadian rhythms that have a periodicity of about, but not exactly 24 hours. Why is this? And to what extent can variation in periodicity in circadian rhythms among the ...
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Delay of sleeping on cortisol cycle

I was told that cortisol has to be measured at 9am or 4pm, because those where its peak level. But I wonder if changes on sleep patters affect the cortisol cycle. I mean, if I usually go to sleep ...
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What is the purpose of Prostaglandin F2-alpha and the Prostaglandin F receptor in the melatonin cell signaling pathway?

I've been doing a lot of research recently on the melatonin cell signaling pathway for an extra credit project at school. I've included an image in this post, which is a diagram of the MT1 pathway. It ...
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How would our circadian rhythm change over time if we had no sunlight whatsoever?

Of course, over the span of a couple days, our circadian rhythms would lengthen a few hours. But what would happen to the circadian rhythms of humans overall if we had no daylight ever? Say we can ...
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Is there a difference between sleeping late and waking up late vs sleeping early and waking up early?

For example, if I sleep at 1 AM and wake up at 10 AM, will it negatively affect my health opposed to sleeping at 10 PM and waking up at 7 AM?
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Does iris color effect the amount of light that reaches photosensitive ganglion cells?

Does eye color (of iris) have any effect on the amount of light reaching retina cells and hence effect melatonin production?
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Circadian Clock During a Flight

I am interested in knowing how our Circadian Clock responds (and if there are resultant changes) when we travel across Time Zones? UPDATE 24th April I am reopening this question as the statement in ...
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How does the body count time in the short term?

So I've done some research and found out about the different circadian cycles that use chemical clocks to help us keep time in the long term (hours, days, etc.). This doesn't seem to explain how we ...
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Does apoptosis occur more at a particular time of day?

I am interested to know if apoptosis (programmed cell death) occurs more frequently during daytime or nighttime hours, e.g. if apoptosis is associated with a circadian rhythm. A simple search turned ...
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How do plants 'tell time' for circadian rhythms based on a ~24 cycle?

I've read that many plants have some sort of circadian rhythm where they perform a certain action on a cycle of about 24 hours, like the mimosa plant opening and closing its leaves. Obviously, this is ...
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Does sleep duration vary for animals based on time of the year?

I'm interested in the sleep patterns of wild animals, that still use sun for controlling their biological clock. Animals entrain their biological clock to the day/night cycle using light as the ...
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Variation of length of circadian rhythm in humans in absense of time reference

Are there any studies which show the range of the length of circadian rhythms for people that are removed from actual time, (Eg no sunset/ sunrise, no clocks or other reference of time)? For example, ...
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What is blue light?

What is the "blue light" often discussed in relation to human melatonin production, sleep/wake cycles, etc.? A Google search seems to define it as light of a particular wavelength, suggesting that it ...
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What causes adenosine build up in the brain when awake?

Adenosine is an important hormone in sleep regulation. It is postulated that when a person is awake, there is a build up of adenosine in the brain, which inhibits the neurons in the brain, and ...
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Do lunar rhythms have impact on human biology, if so, how?

I'm approaching this question from the circadian rhythm perspective. A circadian rhythm is a 24 hour cycle. While doing research on deep sea circadian rhythms, I found this abstract which seemed to ...
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Is the human biological clock genetically programmed or learnt?

Argument favouring learning: A newborn sleeps for 20-22 hours. But overtime (s)he learns to focus sleeping time to night time, according to his or her needs and family needs. Some sleep from 1 am to 7 ...
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Would constant light or fading light be registered as more wakefulness promoting by the Supra Chiasmatic Nucleus?

During the fall and winter season, a number of people are experiencing Seasonal Affective Disorder. One of the way it has traditionally been treated is with a dedicated lightbox - a very high ...
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How can space-time affect ageing? [closed]

I recently watched the movie -"interstellar" and I came through the question that how can ageing be affected by space-time? Wherever I look, I get it as a fact that it's kind of ageing slows down in ...
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Why do we weigh less in the morning?

At first I thought it may be related to physics. You know, in one half of the day, the gravity changes, and the scale shows a different weight than the other. Then at night, gravity intensifies, and ...
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Photoperiodism: Short-Day Plants

My Campbell's Biology textbook discusses photoperiodism of plants and introduces us to short-day and long-day plants. What I don't understand is why short day plants will not flower if they are ...
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How did the introduction of artificial light changed the life cycle of a plant?

Plants in urbanized areas are constantly exposed to artificial light after sunset. In their natural habitat there is a more distinct day and night cycle. Since light is an important factor in a plant ...
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How do humans perceive time?

We can see length, and other physical quantities. We can perceive through our other senses like (temperature through thermoreceptors, weight through pressure receptors etc.). But how do we "sense" ...
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How do PER/CRY complexes accumulate in the cytoplasm?

The Period/Cryptochrome (PER/CRY) complex is a heterodimer that transcriptionally regulates circadian rhythm. When it is phosphorylated, it is transported to the nucleus and it inhibits a ...
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What light intensity starts melatonin release in humans?

I'm interested in whether any studies have determined the intensity of light at eye level that starts melatonin release in humans. I know that: melatonin release is suppressed by blue light with ...
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How would a different solar day affect evolution?

Has anyone theorized how evolution would be affected by a different length of solar day, what were the conclusions? The thought came from thinking about life on other planets/moons, but I'm initially ...
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High frequency human genetic oscillators?

The most well studied genetic oscillators in human genomes are involved in regulating the circadian clock (which operates on an approximately 24-hour cycle) and cell cycle activity (with single cycles ...
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Is there a correlation between brain size and amount of sleep? [closed]

As far as we know, sleep seems to be the part of the daily cycle when executive functions are resting and memories are fortifying. Many, but not all, of the functions that become dysfunctional upon ...
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What is the cause of singularity in phase response curve of human sleep and bright light?

I have no background in science as I am a computer programmer, but I am trying to get information on phase response curves, human sleep and exposure to bright light as I am trying to get to grips with ...
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What non invasive methods of estimating Body Time are there?

I found this article on estimating body time using molecular timetable of 168 genes. researchers looked at gene expressions and plotted them to 24 hour cosines curve with some pretty spectacular ...
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Do marine deep sea life forms exhibit circadian rhythms? If so, what entrains them?

I've been reading a lot about circadian rhythms, when suddenly this question popped into my head: do circadian rhythms exist for deep sea organisms (3000 ft / 1000 meters+)? For land mammals, the ...
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What is the mechanism of regulation of PER /CRY genes?

I've read multiple descriptions of biological/circadian clocks and they all mention PER, CRY and CLOCK genes. While I kinda get how they are connected, what interests me is how these actually regulate ...
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Is there a comprehensive list of human circadian-like processes, hormones or gene expressions?

I'm reading this article onblood sugar and circadian rhythms and the following question popped into my head: a lot of articles mention various diurnal or circadian rhythmicity of biological processes. ...
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Is there an optimal illumination level for human habitats/workplaces?

I know of melanopsin, a photo pigment in mammal eye that helps regulate circadian rhythms. It responds most strongly to blue spectrum light. There have been experiments that demonstrated that ...
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Are (baseline) high blood levels of melatonin associated with either circadian rhythm or mood disorders?

(Exogenous) melatonin is administered at night for treatment of circadian rhythm disorders, but melatonin taken during the day is linked with depression. I would like to know if high blood levels of (...
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Is there a normal human melatonin concentration to light level curve?

I'm looking for a graph or a curve that would show the typical concentration of melatonin in blood or saliva for humans over 24 hours. It would be good to know the photoperiod for the same human as ...