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Short answer The biological master clock is neurologically and genetically hardwired. The biological clock is not affected by learning. Instead, it is constantly entrained mainly by daylight. Background The biological clock is hardwired in the human body and can be traced back to the master clock in the suprachiasmatic nuclei (SCN) of the hypothalamus (...


10

Short answer: yes. Although clearly the infradian changes in steroid hormones in females are quite "obvious", other changes are less evident, but happen nonetheless in males as well as in females. Most of the hormones produced by endocrine organs such as the hypothalamus (a region at the base of the brain) or the hypophisis are not secreted in a continuous ...


10

Short answer The increased fear responses during the night are believed to be mediated by elevated corticotropin-releasing hormone (CRH) levels in the brain that drive the fear responses in the amygdala. Background Fear responses can be experimentally assessed by recording the startle reflex. For example, loud noises can evoke gross startle responses in ...


8

When you travel to different time zones, your circadian clock will be off (incorrect). The reason your circadian clock will be off is because your body has adapted to the time zone you are from. When you enter a new time zone, your circadian clock will still be functioning on the old the time zone. If the time zone difference is $\pm 12$ hours, this is a ...


8

There are lots of biological clocks, or clocks made of biological components. The circadian clock is an important, though complicated, example. There are excellent engineered clocks that form some of the neatest examples of systems / synthetic biology. See for example Elowitz & Leibler's "repressilator" (link, link). The basic idea in all of these is to ...


7

The question piqued my interest, but after hunting through the literature for a bit, I hadn't found any direct answers. Then I went back and read the mouse study you cited a bit more carefully. The mouse study only made a reference to mice being affected at 4 lux, ~100x more sensitive than humans. However, for that number it cited a paper in Science that ...


6

I found this - Celec et al. (2003) Circatrigintan cycle of salivary testosterone in human male. Biological Rhythm Research 34: 305-315 Conclusion. We believe that this is the first study demonstrating the existence of circatrigintan and circavigintan rhythms of testosterone in human males. Our findings might have implications in human physiology and ...


6

Adenosine causes humans to become sleepy. But how ? During day time we consume food which is broken down into glucose. This glucose is broken down by "Glycolysis" in cell's cytoplasm during which ATP is produced. This produced ATP is is then used by body as an energy supplier. ATP breaks down into ADP and then AMP with the release of energy which our body ...


6

Here are some examples: electric oscillators: neural activity cardiac automatism (0.8 ... 1 Hz) mechanical oscillators (as a result of neural activity): heart beats breathing (0.2 ... 0.3 Hz) intestinal peristaltic waves vocal chords activity (up to a few kHz) muscular spasm (pathological) chemical oscillators: insulin variation in concordance with ...


6

Veritasium created an excellent video just on this topic, which I would recommend watching, but will summarize here. A common misconception is that we lose weight when we digest food or burn calories. Keep in mind that that broken down food and those calories* aren't "going anywhere", so technically you shouldn't loose any mass (unless you get rid of the ...


5

There is indeed a slight weight variation during the day. About 2 - 4 lbs (approx. 1 - 2 kg) [1, 2]. Some causes are: water loss through respiration, perspiration or urination [1]. the relative long period without eating and drinking [2]. metabolic processing of food and drinks during sleep. References: Cindy Banyai. http://www.livestrong.com/article/...


5

A research paper that recently came out suggests that deep-sea life does have a circadian rhythm, but it is regulated much differently than it is by us surface dwellers. We see light, we eat and digest, and the suprachiasmatic nucleus in the brain (our "biological" clock) keeps track of it and eventually establishes a rhythm of the circadian variety. Most ...


4

The situation is quite complex, and there are certain things that we do not fully understand, but I will try to give you an explanation. First of all, at the cellular level, you have the genetic components of the circadian clock, the clock genes and their protein products. You can divide clock proteins into positive and negative regulators: the positive ...


4

According to this study, artificial lighting similar to that provided by streetlights in the UK can reduce flowering in at least one plant, which also affects the aphids that feed on it. This article discusses it in more general terms - night lighting doesn't affect photosynthesis, but can affect the length of day/night perceived by plants and alter growth ...


4

The nature of time has been discussed for millenia. We don't know exactly why or where time perception exists, but we do have some information on how it is perceived. The circadian rhythm is basically in place to help us sleep, wake and perform tasks in a 24 hour cycle of light. Robbed of light, and the melatonin it's absence produces, the rhythm shifts ...


4

Blue light means wavelengths that appear to the human eye as blue when they are presented alone. This light is important for sleep/wake cycle regulation because this is the wavelength that cells that participate in this regulation respond to. "White light" is light that covers the full visible spectrum; sunlight, for example, is fairly white. However, that ...


3

Humans and many other organisms have a circadian clock, a biological system that oscillates every 24 hours (but is also sensitive to external stimuli). There are many components to the human circadian clock that are not known. On the molecular level, gene regulation, post-transcriptional and post-translational modification are all implicated. There is also ...


3

Yes, the human body has thermoreceptors that "sense" the current temperature, but these merely help with regulation--you know, shivering to raise internal body temperature and sweating to cool via evaporation. The hypothalamus is primarily responsible for making sure that the circadian rhythm itinerary is adhered to reasonably well. So no, if the ...


3

The main effect, of vitamin B6, is neurological, becouse moderate variations in the intracellular concentration of pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, can have pronounced modulatory effects on steroid-induced gene expression. So you cannot get the effect of stress hormones. Also neurological damage has been reported ...


3

(too long to be a comment) You may be interested in http://en.wikipedia.org/wiki/Phase_response_curve. This graph shows how the body's circadian rhythm normally works: http://en.wikipedia.org/wiki/File:Body_Temp_Variation.png. Body temperature decreases during the night (apparently due to more melatonin production. I conjecture that the proposed schedule ...


3

For circadian rhythm, the gold standard is melatonin secretion (blood or saliva). Also, core body temperature. see: Circadian temperature and melatonin rhythms, sleep, and neurobehavioral function in humans living on a 20-h day James K. Wyatt , Angela Ritz-De Cecco , Charles A. Czeisler , Derk-Jan Dijk American Journal of Physiology - Regulatory, ...


3

According to Einstein's Special Theory of Relativity, moving objects measure shorter in their direction of motion as their velocity increases until, at the speed of light, they disappear. It also tells us that moving clocks run more slowly as their velocity increases until, at the speed of light, they stop running altogether. Hence, astronauts traveling ...


3

This might be the study to which you refer in your answer, the people tested averaged a daily cycle of 24 hours and 11 minutes with a surprisingly small variation in their rhythms: The variation between our subjects, with a 95 percent level of confidence, was no more than plus or minus 16 minutes, a remarkably small range. Worth noting they were all ...


3

Circadian rhythms are entrained by light via the suprachiasmatic nucleus, a part of the brain that receives signals from special retinal ganglion cells that are directly sensitive to (mainly blue) light. However, light is not strictly necessary: the internal circadian clock is the result of shifting gene expression that proceeds without outside stimulus. ...


2

Wikipedia gives a very good explanation of this, on the page for the suprachiasmatic nucleus. For example, in the fruitfly Drosophila, the cellular circadian rhythm in neurons is controlled by two interlocked feedback loops. In the first loop, the bHLH transcription factors clock (CLK) and cycle (CYC) drive the transcription of their own ...


2

There isn't a central/master website that I'm aware of, as it's still an area of active research. I did a bit of work in the field about 10 years ago, and at that point we were still working out the circadian rhythms in the yeast mating cycle. Since then, the field been enumerating more and more involved processes: mRNA expression, mRNA degradation, micro ...


2

I found a recent PLoS article that said that none of hypochondriasis, depression, hysteria, psychopathic deviate, masculinity-femininity, psychasthenia, schizophrenia, or social intraversion (on the MMPI-2) "were associated with any melatonin parameter." However, it does appear that "increases scores of Hypomania and Paranoia were associated with a shorter ...


2

It depends on how different. Day length affects more than just how long the periods of light and dark are. Let's assume a very slow rotation, and a very long day, maybe 1 month light, 1 month dark. The light side would get much warmer while the dark side would get much cooler. At the border between light and dark sides, you'd expect to see powerful storms as ...


2

Yes, people, as well as animals regulate their drowsiness by light. There's a well known experiment conducted by Michel Suffre on himself in 1972. When he spent a month with no light and no information about the time, his sleeping cycles prolonged up to 48 hours.


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