How does the body know how much to sleep?

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My question is suppose we go to sleep without setting an alarm and intending to get up only when we wake up. How does the body know that it needs X hours of sleep at night. Is our subconsciousness monitoring our stress levels and when it has determined that our stress level is sufficiently low or it has crossed a sufficient threshold, do we wake up or is something else going on. Thoughts?
 

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  • #2
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I would think it difficult to eliminate all outside factors, including basic body functions, in order to test.
 
  • #3
Drakkith
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Well, take a look at this: http://en.wikipedia.org/wiki/Sleep

Sleep timing is controlled by the circadian clock, sleep-wake homeostasis, and in humans, within certain bounds, willed behavior. The circadian clock—an inner timekeeping, temperature-fluctuating, enzyme-controlling device—works in tandem with adenosine, a neurotransmitter that inhibits many of the bodily processes associated with wakefulness. Adenosine is created over the course of the day; high levels of adenosine lead to sleepiness[citation needed]. In diurnal animals, sleepiness occurs as the circadian element causes the release of the hormone melatonin and a gradual decrease in core body temperature. The timing is affected by one's chronotype. It is the circadian rhythm that determines the ideal timing of a correctly structured and restorative sleep episode.[17]

Homeostatic sleep propensity (the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode) must be balanced against the circadian element for satisfactory sleep.[18] Along with corresponding messages from the circadian clock, this tells the body it needs to sleep.[19] Sleep offset (awakening) is primarily determined by circadian rhythm. A person who regularly awakens at an early hour will generally not be able to sleep much later than his or her normal waking time, even if moderately sleep-deprived.
 
  • #4
I watched an interesting show on this subject a few years back. It followed a number of 'cavers'--scientists and geologists who would spend weeks underground exploring and mapping miles-long cave systems. They obviously had no conventional cycles of light and dark to influence waking and sleep patterns, and just allowed their bodies to determine the proper amount of sleep as needed. It turned out that, after a number of days, their internal 'day' and 'night' periods became progressively longer, so that they were eventually living on something like a 25 or 26 hour cycle. I don't know how that correlates to anything evolutionary, since it's my understanding that days were actually shorter in the past than they are now. Still, it's an interesting observation.
 
  • #5
Drakkith
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Yeah, I remember reading something similar to that where they put people in rooms with no way to tell time at all. The people ended up lengthening their day gradually.
 
  • #6
Ryan_m_b
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I watched an interesting show on this subject a few years back. It followed a number of 'cavers'--scientists and geologists who would spend weeks underground exploring and mapping miles-long cave systems. They obviously had no conventional cycles of light and dark to influence waking and sleep patterns, and just allowed their bodies to determine the proper amount of sleep as needed. It turned out that, after a number of days, their internal 'day' and 'night' periods became progressively longer, so that they were eventually living on something like a 25 or 26 hour cycle. I don't know how that correlates to anything evolutionary, since it's my understanding that days were actually shorter in the past than they are now. Still, it's an interesting observation.
I'd heard that results like this are bunk, even though they are widely reported, and are the result of faulty experimental conditions. I'll see if I can find more about that.

As for the day length over time there has been no significant change in the history of our species.
 
  • #7
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A bit off-topic regarding sleep, but shows an effect when time is uncertain.
 
  • #8
Drakkith
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A bit off-topic regarding sleep, but shows an effect when time is uncertain.
I'm sorry, what? I don't quite understand what you are saying.
 

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