Sleep is one of those funny things about being a human
being -- you just have to do it. Have you ever wondered why?
And what about the crazy dreams, like the one where a bad
person is chasing you and you can't run or yell. Does that
make any sense?
If you have ever wondered about why people have to sleep or
what causes dreams, then read on. In this edition of HowStuffWorks,
you'll find out all about sleep and what it does for you.
Characteristics of Sleep
We all know how
sleep looks -- when we see someone sleeping, we recognize the
In addition to these
outward signs, the heart slows
down and the brain does
some pretty funky things (we'll get to this later).
- If possible, the person will lie down to go to sleep.
- The person's eyes are closed.
- The person doesn't hear anything unless it is a loud
- The person breathes in a slow, rhythmic pattern.
- The person's muscles
are completely relaxed. If sitting up, the person may fall
out of his or her chair as sleep deepens.
- During sleep, the person occasionally rolls over or
rearranges his or her body. This happens approximately once
or twice an hour. This may be the body's way of making sure
that no part of the body or skin has its circulation cut off
for too long a period of time.
In other words, a sleeping person is unconscious to most
things happening in the environment. The biggest difference
between someone who is asleep and someone who has fainted or
gone into a coma is the fact that a sleeping person can be
aroused if the stimulus is strong enough. If you shake the
person, yell loudly or flash a bright light, a sleeping person
will wake up.
For any animal living in the wild, it just doesn't seem
very smart to design in a mandatory eight-hour period of
near-total unconsciousness every day. Yet that is exactly what
has done. So there must be a pretty good reason for it!
How Much Sleep Do I
Need?Most adult people
seem to need seven to nine hours of sleep a night. This
is an average, and it is also subjective. You, for
example, probably know how much sleep you need in an
average night to feel your best.
The amount of sleep you need decreases with age. A
newborn baby might sleep 20 hours a day. By age four,
the average is 12 hours a day. By age 10, the average
falls to 10 hours a day. Senior citizens can often get
by with six or seven hours a day.
Reptiles, birds and mammals all
sleep. That is, they become unconscious to their surroundings
for periods of time. Some fish and amphibians reduce their
awareness but do not ever become unconscious like the higher
vertebrates do. Insects do not appear to sleep, although they
may become inactive in daylight or darkness.
By studying brainwaves, it is known that reptiles do not
dream. Birds dream a little. Mammals all dream during sleep.
Different animals sleep in different ways. Some animals,
like humans, prefer to sleep in one long session. Other
animals (dogs, for example) like to sleep in many short
bursts. Some sleep at night, while others sleep during the
Really?Cows can sleep while standing up, but
they only dream if they lie down!
Whales and dolphins are "conscious breathers,"
and they need to keep breathing while they sleep, so
only one half of the brain sleeps at a time! (Click
Sleep and the Brain
If you attach an
electroencephalograph to a person's head, you can
record the person's brainwave activity. An awake and relaxed
person generates alpha waves, which are consistent
oscillations at about 10 cycles per second. An alert person
generates beta waves, which are about twice as fast.
During sleep, two slower patterns called theta waves
and delta waves take over. Theta waves have
oscillations in the range of 3.5 to 7 cycles per second, and
delta waves have oscillations of less than 3.5 cycles per
second. As a person falls asleep and sleep deepens, the
brainwave patterns slow down. The slower the brainwave
patterns, the deeper the sleep -- a person deep in delta wave
sleep is hardest to wake up.
At several points during the night, something unexpected
happens -- rapid eye movement (REM) sleep occurs. Most
people experience three to five intervals of REM sleep per
night, and brainwaves during this period speed up to awake
levels. If you ever watch a person or a dog experiencing REM
sleep, you will see their eyes flickering back and forth
rapidly. In many dogs and some people, arms, legs and facial
muscles will twitch during REM sleep. Periods of sleep other
than REM sleep are know as NREM -- non-REM -- sleep.
REM sleep is when you dream. If you wake up a person
during REM sleep, the person can vividly recall dreams. If you
wake up a person during NREM sleep, generally the person will
not be dreaming.
You must have both REM and NREM sleep to get a good night's
sleep. A normal person will spend about 25 percent of the
night in REM sleep, and the rest in NREM. A REM session -- a
dream -- lasts five to 30 minutes.
Medicine can hamper your ability to get a good night's
sleep. Many medicines, including most sleeping medicines,
change the quality of sleep and the REM component of it.
One way to understand why we
sleep is to look at what happens when we don't get enough:
A person who gets just a few hours of
sleep per night can experience many of the same problems over
- As you know if you have ever pulled an all-nighter,
missing one night of sleep is not fatal. A person will
generally be irritable during the next day and will either
slow down (become tired easily) or will be totally wired
because of adrenalin.
- If a person misses two nights of sleep, it gets worse.
Concentration is difficult, and attention span falls by the
wayside. Mistakes increase.
- After three days, a person will start to hallucinate and
clear thinking is impossible. With continued wakefulness a
person can lose grasp of reality. Rats forced to stay awake
continuously will eventually die, proving that sleep is
Two other things are known to happen during sleep. Growth
hormone in children is secreted during sleep, and chemicals
important to the immune
system are secreted during sleep. You can become more
prone to disease if you don't get enough sleep, and a child's
growth can be stunted by sleep deprivation.
But the question remains -- why do we need to sleep? No one
really knows. There are all kinds of theories, including
What we all know is that, with a good night's sleep,
everything looks and feels better in the morning. Both the
brain and the body are refreshed and ready for a new day.
- Sleep gives the body a chance to repair muscles
and other tissues, replace aging or dead cells, etc.
- Sleep gives the brain a
chance to organize and archive memories. Dreams are thought
by some to be part of this process.
- Sleep lowers our energy consumption, so we need three
meals a day rather than four or five. Since we can't do
anything in the dark anyway, we might as well "turn off" and
save the energy.
- According to this
article, sleep may be a way of recharging the brain,
using adenosine as a signal that the brain needs to rest:
"Since adenosine secretion reflects brain cell activity,
rising concentrations of this chemical may be how the organ
gauges that it has been burning up its energy reserves and
needs to shut down for a while." Adenosine levels in the
brain rise during wakefulness and decline during sleep.
Tips to Improve Your
regularly. Exercise helps tire and relax your body.
- Don't consume caffeine
after 4:00 p.m. or so. Avoid other stimulants like cigarettes
- Avoid alcohol
before bedtime. Alcohol disrupts the brain's normal
patterns during sleep.
- Try to stay in a pattern with a regular bedtime
and wakeup time, even on weekends.
Why do we have such crazy, kooky
dreams? Why do we dream at all for that matter? According to
Joel Achenbach in his book Why
The brain creates dreams through random electrical
activity. Random is the key word here. About every 90
minutes the brain stem sends electrical impulses throughout
the brain, in no particular order or fashion. The analytic
portion of the brain -- the forebrain -- then desperately
tries to make sense of these signals. It is like looking at
a Rorschach test, a random splash of ink on paper. The only
way of comprehending it is by viewing the dream (or the
inkblot) metaphorically, symbolically, since there's no
Here are some other things you may have noticed about
This doesn't mean that dreams are meaningless or should
be ignored. How our forebrains choose to "analyze" the
random and discontinuous images may tell us something about
ourselves, just as what we see in an inkblot can be
revelatory. And perhaps there is a purpose to the craziness:
Our minds may be working on deep-seated problems through
these circuitous and less threatening metaphorical dreams.
- Dreams tell a story. They are like a TV show, with
scenes, characters and props.
- Dreams are egocentric. They almost always involve you.
- Dreams incorporate things that have happened to you
recently. They can also incorporate deep wishes and fears.
- A noise in the environment is often worked in to a dream
in some way, giving some credibility to the idea that dreams
are simply the brain's response to random impulses.
- You usually cannot control a dream -- in fact, many
dreams emphasize your lack of control by making it
impossible to run or yell. (However, proponents of lucid
dreaming try to help you gain control.)
Dreaming is important. In sleep experiments where a person
is woken up every time he/she enters REM sleep, the person
becomes increasingly impatient and uncomfortable over time.
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