Questions tagged [sleep]

The biological process characterized by reversible unconsciousness, unresponsiveness to external stimuli and motor passivity.

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Why did the process of sleep evolve in many animals? What is its evolutionary advantage?

The process of sleep seems to be very disadvantageous to an organism as it is extremely vulnerable to predation for several hours at a time. Why is sleep necessary in so many animals? What advantage ...
Gordon Gustafson's user avatar
8 votes
2 answers
926 views

Why do we sleep?

While we do know that the human body is regulated by a circadian clock that keeps humans on a sleep/wake cycle, we don’t really know why. Sleep is the time when our bodies repair tissues and perform ...
Sajin Shereef's user avatar
6 votes
5 answers
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Why do the humans become sleepy after meals?

I don't know about all the mankind, but I know enough people, who becomes sleepy after their meals. Also, I'm not sure, what kind of food do they consume, but I personally get sleepy almost from any ...
abyss.7's user avatar
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66 votes
2 answers
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Do ants or other insects sleep, and if so why?

I was thinking yesterday about insects (as there was a spider in the house, and I couldn't help but think of anything else, even though they aren't insects), and I started to wonder if ants sleep? ...
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13 votes
1 answer
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What senses are active while sleeping?

During sleep, our body activity decreases. I am wondering on the extent of the lowering of this activity regarding our five senses. Clearly, the sense of touch is still very efficient since shaking a ...
Taladris's user avatar
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10 votes
1 answer
308 views

Which part of human eyes is getting tired?

It's a thing of common sense that if you read, drive or look at computer screen for too long your eyes will get tired. They burn, itch and try to close all the time. But I was wondering which part(s) ...
Tomáš Zato's user avatar
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9 votes
1 answer
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What causes Paresthesia (Pins and Needles) at a cellular level?

I've looked it up in plenty of places like the Wikipedia page and such, and it is clear that the most common cause of Paresthesia is either a fair amount of pressure on a specific patch of skin ...
Ethan's user avatar
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6 votes
1 answer
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What causes humans to be sleepy?

Is there a hormone or group of hormones that regulates when we feel sleepy late at night, or in the morning? Or is sleepiness caused by some other non-hormonal mechanism? (e.g. pure psychological, ...
Kenshin's user avatar
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21 votes
1 answer
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Why do we feel tired if we sleep excessively?

When we eat, finally we feel full. I know which mechanism causes the sensation of being full. But when we sleep excessively we often still want more sleep. Why does this happen? Is there a mechanism ...
MySky's user avatar
  • 2,264
19 votes
2 answers
895 views

Can parts of a human brain be asleep independently of each other, or vary in the times required for them to fall asleep?

I know that some birds and marine animals can continue complicated activity (swimming, flying?) while one hemisphere of their brain is asleep. I'm interested if human brain has some parts of it that ...
Alex Stone's user avatar
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15 votes
1 answer
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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 ...
Alex Stone's user avatar
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12 votes
1 answer
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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 ...
Kenshin's user avatar
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12 votes
3 answers
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How are our senses dimmed during sleep?

Our senses are not as sensitive during sleep compared to wake. There is an arousal threshold during sleep that only when it is overcome will it wake a person up. My question is how is this arousal ...
dayuloli's user avatar
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11 votes
2 answers
2k views

Why sleep? No, actually, why wake?

I was just reading the sleep threads, and I wondered, why is the body so constructed so that sleep is necessary? (Is it just a design error?) But then, how do things come to be awake at all? How did ...
RedSonja's user avatar
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9 votes
1 answer
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Human sleep cycles and dream times, what influences the timing and intensity? Sleep history included

I'm doing sleep and dreams research and have developed an iPhone application to help me track my bedtime, rise time, sleep onset and also mark dreams. The app also monitors overall activity overnight ...
Alex Stone's user avatar
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9 votes
1 answer
6k views

Effects of Polyphasic vs Monophasic sleep in humans

Why do humans practice monophasic sleep cycles? When altering one's circadian rhythm to a Polyphasic sleep schedule, how much would that affect development? Is Monophasic sleep (once per day) ...
Gabriel Fair's user avatar
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8 votes
2 answers
1k views

Is it possible to live without health problems sleeping one day and not the other?

Basically, I want to know if it would be humanely possible to sleep one day, skip the next, sleep, skip, sleep, skip, etc, with a 8 hour sleep time. If you need any extra information, let me know.
Pedro's user avatar
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6 votes
1 answer
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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 ...
Alex Stone's user avatar
  • 6,517
6 votes
1 answer
601 views

What is happening physically when I get sleepy and when I wake up?

After a week of too little sleep, I slept about 12 hours last night to "catch up". It made me wonder: what is happening physically that signals that I'm done sleeping, or conversely, that I need to ...
user avatar
6 votes
3 answers
26k views

Why do our eyes close when we sleep?

Why do our eyes close when we sleep? Is it to relax our eye muscles? How can it be explained from an evolutionary point of view?
Pranay Aryal's user avatar
5 votes
2 answers
521 views

How would the human body adjust to sleep times if we were to live in a place with different day lengths?

You sleep at night and are active during the day that's how things work for humans, but theoretically if a human whose parents lived on earth were to be born in another planet resembling earth but the ...
AllenZ41's user avatar
4 votes
2 answers
686 views

The least complex animals with ability to dream

People can dream, dogs can dream, cats probably too when they are sleeping. What about other creatures? Can a bird dream? Do rats have dreams? Are there any studies about that kind of thing? What ...
Derfder's user avatar
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4 votes
0 answers
65 views

How widespread among mammals is the glymphatic system's metabolite clearance in the brain during sleep currently known to be?

The glymphatic system and "brain washing" (metabolite clearance) during mammalian sleep: Xie et al. (2013) Sleep Drives Metabolite Clearance from the Adult Brain (also here) has been cited ...
uhoh's user avatar
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3 votes
0 answers
195 views

What controls the feeling of discomfort/comfort before and after sleep?

I'm interested in which biological systems or hormones are involved in the following phenomenon: Before sleep it may be difficult to find a comfortable position, and muscular aches and pains are more ...
Alex Stone's user avatar
  • 6,517
3 votes
1 answer
961 views

How are melatonin levels measured in humans?

I'm wondering how it is possible to measure diurnal variations of melatonin levels in humans. I keep reading that there should be a large difference in amplitude between melatonin levels measured at ...
Alex Stone's user avatar
  • 6,517
3 votes
1 answer
478 views

Where do butterflies sleep?

Do butterflies (insects) sleep, and if so, where?? I have googled for information but didn't get an exact answer.
SabareeshSS's user avatar
3 votes
1 answer
241 views

Involuntary twitches and apnoea during early phases of sleep

I assume most people either experienced or have seen people with the following phenomenon: in the early phases of sleep sometimes involuntary twitches occur that usually accompany the pause of ...
Nandor Poka's user avatar
  • 3,098
3 votes
2 answers
146 views

Do dolphins really sleep?

I have always wondered, if dolphins sleep with one eye opened, do they really sleep at all? According to this article dolphins indeed shut down their brains. I already googled it. No help from ...
luchosrock's user avatar
3 votes
2 answers
181 views

Is once per day the optimal sleep pattern for all mammals?

If a typical human body clock is 8 hours sleep, 16 hours awake, interested to know if any mammals have: a 12 hour body clock (4 hours sleep, 8 hours awake) a 6 hour body clock (2 hours sleep, 4 hours ...
stevec's user avatar
  • 217
2 votes
1 answer
1k views

Why does non-continuous sleep makes you feel tired?

Let's say, hypothetically, that you fell asleep at 10PM, and you were woken up by a noise at 1AM. If you went back to sleep immediately and woke up at 6AM, you will feel tired even though you had ...
IxariusSci's user avatar
2 votes
0 answers
442 views

External sensory stimuli that awaken a person from sleep

An external sound or touch can awaken someone. Can a light? It would have to be very strong, but part of the reason might be that it would have to penetrate the eyelids. And can a smell or taste? ...
h34's user avatar
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