Why do we sleep?

Question

I've heard of a substance that we rebuild during sleep but I can't think of what they're called. If you can explain more about sleep to me also, it would be appreciated.

I don't think "neuro-transmitters" are what I'm thinking of, though this, so far, is the closest type of answer to what I'm looking for.

Answer 1

(m)

Sleep is one of the few universal behaviors. Sleep is seen even in species that would seem better off without sleep, for example, the Indus dolphin. Living in muddy waters, over the ages, it has become blind, presumably because vision is not useful in their natural habitat. However, despite the dangers caused by sleeping, sleep has not disappeared. It never stops swimming; doing so would result in injury, because of the dangerous currents and the large amounts of debris carried by the river during the monsoon season. Studies showed that they slept a total of seven hours a day, in very brief naps of four to sixty seconds each. If sleep did not perform an important function, we might expect that, like its vision, sleep would have been eliminated in this species through the process of natural selection

Answer 2

Every creature needs to rest. Giraffes, little babies, elephants, dogs, cats, kids, koala bears, grandparents, moms, dads, and hippos in the jungle - they all sleep! Just like eating, sleep is necessary for survival.

Sleep gives your body a rest and allows it to prepare for the next day. It's like giving your body a mini-vacation. Sleep also gives your brain a chance to sort things out. Scientists aren't exactly sure what kinds of organizing your brain does while you sleep, but they think that sleep may be the time when the brain sorts and stores information, replaces chemicals, and solves problems.

The amount of sleep a person needs depends a lot on his or her age. Babies sleep a lot - about 14 to 15 hours a day! But many older people only need about 7 or 8 hours of sleep each night. Most kids between the ages of 5 and 12 years old are somewhere in between, needing 10 to 11 hours of sleep. Some kids might need more and some need less. It depends on the kid.

Skipping one night's sleep makes a person cranky and clumsy. After missing two nights of sleep, a person will have problems thinking and doing things; his or her brain and body can't do their normal tasks nearly as well. After five nights without sleep, a person will hallucinate (this means seeing things that aren't actually there). Eventually, it becomes impossible for the brain to give its directions to the rest of the body without sleep - the brain needs to spend time in bed and catch its ZZZs!

Answer 3

The substance you are talking about-that we rebuild during our sleep is called 'Neurotransmitters'Neurotransmitters is not a single molecule but a collection of many different types of molecule.
Typically,there are two categories into which we classify these molecules:
1.Excitatory-which cause brain cells to increase theirfunction.
2.Inhibitory-which decreases the cell function.
There is a balance between amount of both types of these molecules.

During stress and activity,the excitatory molecules are used up,and the relative amount of inhibitory molecules increase which causes decrease of brain cell function,which causes sleep!

Answer 4

Theories about the functions of sleep date back thousands of years. Most see the purpose of sleep in terms of rest and recovery from the "wear and tear" of wakefulness. One cannot really argue with this idea as it makes so much sense, and besides, we all know that we feel the "worse for wear" without sleep, and so much better after sleep. However, there is little or no evidence that outside the brain any other organ undergoes any heightened degree of repair during sleep (Horne, 1988). All the evidence so far shows that these other organs undergo their restoration equally effectively (and probably more so) during relaxed wakefulness. The stimulus to the repair of tissue wear and tear is an increase in amino acid levels in the blood, following food absorbtion by the gut. These amino acids are selectively taken up by cells to be synthesised into new protein(i.e. anabolism) to replace old and degraded protein (apart from water, tissue is largely comprised of protein). This repair is facilitated by physical rest, but it does not have to be sleep - relaxed wakefulness is sufficient. During human nighttime sleep, blood amino acid levels usually fall owing to the absence of eating, and consequently, tissue repair is reduced. Anabolism requires much energy, and it has been estimated that over half of our resting metabolic rate is due to anabolic activities. If these increased significantly throughout the body during sleep, then metabolic rate and oxygen consumption would rise substantially. This doesn't happen, but falls somewhat instead (see above).

Humans show a marked surge in growth hormone output during the early part of sleep, which is largely associated with stages 3 and 4 sleep. If one remains awake at this time then this surge isabsent. This sleep-related growth hormone release is rare in other mammals, and has little to do with tissue growth and repair, at least in the human adults. It is probably linked to the rather unusual fasting state which develops in human sleep, and it should be remembered that human nighttime sleep tends to be quite lengthy in comparison with that of many other mammals. Few other mammals actually enter a fasting state during sleep. Herbivores continue to digest food throughout their sleep, carnivores gorge themselves on meat which can take up to a day to digest, and rodents wake up periodically to nibble more food. The human sleep-related growth hormone surge may be a mechanism to protect tissue protein against potentially decremental effects of this fast, and also to promote the body's mobilisation of its fat reserves (Horne, 1988).

Cell division in many tissues also shows a daily surge late at night and in the small hours of the morning, often coinciding with stages 3 and 4 sleep, the growth hormone rise, and again suggesting that sleep promotes general growth and repair. However, the increase in mitosis is not due to sleep, or to the growth hormone, as it is still evident if one remains awake at this time. This daily cycle in cell division is largely associated with feeding activity and a sleep-independent circadian rhythm. An increase in mitosis typically occurs a few hours after a meal (i.e. allowing for the preliminary digestion, food absorbtion, cell repair and growth), particularly when we are resting.

Apart from viewing sleep as some sort of recovery process, most of the early theories about sleep function only looked at the the "how" of sleep and mechanisms that produce sleep, rather than whatsleep does. For example, believing sleep to be the result of a build up of some substance in the brain during wakefulness, that is dissipated during sleep.

Unlike many organs, the cerebral cortex is unable to switch off to any degree, outside sleep. Even when we lie down, turn off the light, relax but remain awake, block out sound and try and clear ourminds of all thoughts, the cortex is always in a state of quiet readiness, prepared to respond immediately to any stimulus. In this respect the waking cerebrum is like a computer, where the power consumption is near to its peak, whether it is idling on standby, awaiting instructions, or is involved with programs and taking in information. This may be why the obvious effects of human sleep deprivation are on behaviour, because the cerebrum needs to sleep, and cannot obtain any rest during wakefulness. If such rest is required for the recovery and restitution of neural and related tissues, then sleep is the only provider of this facility. The more advanced the cerebrum, as in humans, the greater the role sleep may have in this recovery."

Answer 5

Theories regarding the function of sleep:

* Restorative theories of sleep describe sleep as a dynamic time of healing and growth for organisms. For example, during stages 3 and 4, or slow-wave sleep, growth hormone levels increase, and changes in immune function occur. In some studies sleep deprivation has led to decrements in immune function and, under extreme, extended sleep deprivation regimes, altered metabolism. [citation needed] However, short periods of sleep deprivation have not been conclusively shown to significantly impact organ, muscular, cardiac, or other somatic function in ways that suggest that any of these systems are primarily influenced by sleep.

* Non-REM sleep may be an anabolic state marked by physiological processes of growth and rejuvenation of the organism's immune, nervous, muscular, and skeletal systems (but see above). Sleep might restore neurons and increase production of brain proteins and certain hormones. Wakefulness may perhaps be viewed as a cyclical, temporary, hyperactive catabolic state during which the organism acquires nourishment and procreates. Also, during sleep, an organism is vulnerable; when awake it may perceive and avoid threats. Asking the question "Why do we awaken?" instead of "Why do we sleep?" yields a different perspective toward understanding how sleep and its stages contribute to a healthy organism.

* According to the ontogenetic hypothesis of REM sleep, the activity occurring during neonatal REM sleep (or active sleep) seems to be particularly important to the developing organism (Marks et al., 1995). Studies investigating the effects of deprivation of active sleep have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, decreased brain mass (Mirmiran et al. 1983), and an abnormal amount of neuronal cell death (Morrissey, Duntley & Anch, 2004).

* One process commonly believed to be highly dependent on sleep is memory. REM sleep appears to help with the consolidation of spatial and procedural memory, while slow-wave sleep helps with the consolidation of declarative memories. When experimental subjects are given academic material to learn, especially if it involves organized, systematic thought, their retention is markedly increased after a night's sleep. On the other hand, the effectiveness of mere rote memorization is similar with or without an intervening period of sleep. Some memory theorists argue that saving memory directly into long-term memory is a slow and error prone process, and propose that cerebral input is saved first in a temporary memory store, and then encoded and transferred into long-term memory during sleep. (Zhang, 2004).

* Despite an abundance of positive findings in support of these ideas, many sleep scientists do not believe that sleep's primary function is related to memory. These scientists point out that many of the studies cited by proponents of this theory are contradictory or confounded by the side-effects caused by the experimental manipulations. A more salient issue is that only a handful of studies have shown that sleep actually influences brain plasticity--which is the mechanism underlying remembering and forgetting (Benington and Frank, 2003).

* One view, "Preservation and Protection", is that sleep serves an adaptive function. It protects the individual during that portion of the 24-hour day in which being awake, and hence roaming around, would place the individual at greatest risk. Organisms don't require 24 hours to feed themselves and meet other necessities. From this perspective of adaptation, organisms are safer by staying out of harm's way where potentially they could be prey to other stronger organisms. They sleep at times that maximize their safety, given their physical capacities and their habitats. (Allison & Cicchetti, 1976; Webb, 1982). This theory, however, is not universally accepted. For example, if true, there would be no reason for the brain to disengage from the external environment as it does during normal sleep. A more advantageous adaptation would be for animals to seclude themselves but maintain quiet wakefulness to avoid predation. Sleep is not simply a passive consequence of removing the animal from the environment, but rather is itself a "drive": animals will alter their behaviors in order to obtain sleep. Therefore, circadian regulation is more than sufficient to explain periods of activity and quiescence that are adaptive to an organism, but the more peculiar specializations of sleep most likely reflect different and unknown functions.

These several theories are not mutually exclusive; each may contain truths that will be validated in the future. Despite decades of intense research, scientists still have only clues to sleep function. With the recent demonstration that sleep is phylogenetically ancient (Shaw et al Science 2000, Hendricks et al Neuron 2000), the focus for understanding the purpose of sleep shifts from humans and other mammals to simple animals that predated the emergence of arthropoda and chordata phyla. Therefore, some of the sleep features that are unique to mammals (e.g. REM sleep and thermoregulation) are unlikely to have played a role in the evolution of a sleep-like state in the premordial metazoan. An examination of the nature of sleep and of wakefulness thus turns its focus to the study of the roles that proteins and enzymes play in basic metabolism.

Answer 6

Go without sleep and the effects will be obvious and progressively dramatic. Your attention and learning abilities will dwindle quickly. Your metabolic rate will shoot up. Your body will be unable to regulate its temperature. At some point you will start hallucinating. We don't know how long a human can go without sleep, but a rat drops dead, of infection, after three sleepless weeks.
In spite of these dramatic symptoms, however, why we sleep is far from clear, particularly when the question is framed by our evolutionary history. Why would an animal with few innate defense skills to start with further place itself at risk by descending into unconsciousness for better than one-third of every day? Under such circumstances, sleep makes no sense--unless it serves a greater need.

Many reasons have been proposed, but most are no more satisfying than one offered by Aristotle, that sleep served to cool the brain. Many basic physiological needs can be met simply with rest. And besides, sleep does not seem to stem immediately from bodily needs, since the first symptoms of sleep loss show up in the brain.

In short, the average person spends 27 years asleep, so unless all our ideas about evolutionary expediency are wrong, sleep must serve some very important function! James Krueger, a sleep researcher at Washington State University, has an explanation that might persuade you to set your alarm just a little later.

About an hour and a half after you fall asleep, you enter a phase called REM

sleep, so called because your eyes dart rapidly during this phase, reflecting the activity of your brain. French sleep researcher Michel Jouvet called REM "paradoxical" sleep, for even though you are deep asleep, your brain waves are hardly distinguishable from the preceding light transitional state.

Until the sleep research pioneer Nathaniel Kleitman published Sleep and Wakefulness in 1939, the general scientific perception was that nothing much happened during sleep. Sleep was a passive state, forced on the nervous system by the separation of the brain from the rest of body. However, Kleitman's notion that the brain attended to very important business during sleep was strengthened by the discovery of REM sleep 1953 by Eugene Aserinsky, a doctoral student in his lab.

But the discovery of REM sleep simply complicated things, raising a question parallel to the big "why"--what in the world is the brain doing during REM? Even though the body is limp with sleep paralysis, the brain is just as busy as it is while awake.

Krueger believes that REM sleep is when the brain does its housekeeping. All day long the brain is busy processing information, synapses firing on and off, neurons constantly exchanging information and rearranging relationships with their neighbors. Here comes a new thought or sensation, and the appropriate neurons hurriedly form new networks. Information in, information out. In, out. On, off. Hello, goodbye. Thousands of times a day.

Experience actually alters the anatomy, or "microcircuitry," of the brain. Memories, in other words, take on an actual form. If this process goes unchecked, says Krueger, the brain will eventually completely transform itself.

Think: How many memories did you form today? How many fleeting impressions? What did you read, hear, touch, taste, feel? Your brain is much different in the evening than it was 16 hours earlier, its circuitry thoroughly reworked. Somehow, reasons Krueger, it must put itself back in order. For much of who you are, physiologically as well as behaviorally, is genetically patterned. If your brain never gets a chance to step back and ask itself "who am I?" well, then, who IS it after a few days?

Sleep, in other words, affects the "synaptic plasticity" of the brain. It reorders and restores the brain's "synaptic superstructure." It keeps you who you are. It serves to preserve both acquired and inherited behaviors.

The most intriguing thing about Krueger's hypothesis is that it is testable. Only one other lab in the world has such a tangible theory; it is at Stanford and uses a hibernating hamster as a model system. Krueger, on the other hand, uses a rat with half its whiskers shaved.

Rats rely on their whiskers for spatial location. Shaving one side of those whiskers throws their orientation way off.

But immediately, the somatosensory cortex on the side of the brain opposite to the shaved whiskers begins reorganizing itself. This process begins within a few hours of the shave and continues for several days.

What Krueger and the rest of the lab watch for is a pattern of molecular markers, specified molecules involved in the formation of synapses. But what they're particularly interested in is the effect of sleep on that reorganization.

If the semi-whiskered rat is kept from sleeping, the changes seem to be different from the changes in a well-rested rat. If the lack of sleep blocks the synaptic reorganization, then the role of sleep has been further defined. This indeed seems to be the case as the results of the experiment start to materialize.

There's another way to test this idea that sleep tidies and reorganizes. This involves the relation between memory and the hippocampus. Among its other roles, the hippocampus is a short-term memory structure as well as being vital to our understanding where we are.

Gina Poe trains her rats on a simple rectangular runway, with six food stations around the perimeter. Even though they are otherwise identical, only three of the stations actually offer food. The rats' task is to memorize where the food is, which they do after three or four days.

Poe is an electrophysiologist, which means she is very good at measuring electrical impulses in the brain, the sound of synapses, of the brain at work. What sets her lab apart is that it is one of the few in the world capable of monitoring and analyzing groups of over 30 neurons at a time.

Most such monitoring systems use single electrodes, which are sufficient for studying the cortex, where the neurons are relatively far apart. The signals of individual neurons are teased apart by cutting off the amplitude of the signal, and thus losing the fine-tuning necessary for telling one neuron from another--as is necessary in the hippocampus, where the neurons are more tightly packed.

Poe works with an electrode comprising four wires, providing four channels, which are then analyzed with a massive bank of eight Sun System computers, an extraordinarily sophisticated process that Poe learned as a post doc in the lab of Bruce McNaughton at the University of Arizona.

Poe and Krueger are working together with her system to elaborate the synaptic superstructure hypothesis. His expertise in brain biochemistry combined with her electrochemical talents should paint a convincing picture of REM's reorganizational role.

But ideas Poe has pursued lend further elegance to the housekeeping model. Somewhere along the way, she observed that when a rat learns to orient itself, which can take several days of training, immediately before everything clicks for it, just before the "aha," its REM sleep increases.

Closer inspection revealed that the rat's hippocampal neurons were firing in a manner consistent with long-term potentiation, the strengthening of memory. Also, they were firing at its amplitudal peak.

Neurons firing at their amplitudal trough, on the other hand, result in de-potentiation, or paring of memory. So what happens during REM sleep? she wondered. Do cells fire mostly at their peak, strengthening memory? Or do they fire mostly at their trough , breaking apart synapses and perhaps refreshing the hippocampus for learning something new?

The answer, it appears, is both. Neurons associated with memories already well consolidated no longer need the short-term capability of the hippocampus, so they de-potentiate. Somehow those memories are transferred to the cortex. Cells associated with new memories, however, fire during REM at their peak, strengthening, potentiating.

In other words, again, the brain during REM both cleans out and puts things in order. It both strengthens and pares.

Naturally, consolidation and paring of memory is likely only part of sleep's function. Given the severe physiological effects of sleep deprivation, sleep surely has a restorative effect, says Poe. What exactly it is, we're still far from understanding, and much remains for the curious sleep researcher to explore.