UNDERSTANDING SLEEP MECHANICS
Most of the progress in understanding sleep mechanics has been made in
the last 50 years. What has been learned explodes some long-standing
misconceptions. One is the assumption that since many bodily functions slows
down during rest; sleep is little more than a state of inactivity.
By studying brain-wave patterns, medical
researchers have learned that there are repeated cycles and stages of sleep.
Far from being inactive, the human brain runs at high speed during certain
periods of sleep. Healthful sleep involves going through these cycles four or
more times every night and spending a sufficient amount of time in each cycle.
A normal night’s sleep is most easily
divided into 2 types: what is commonly called REM [rapid eye movement, or dream]
sleep and non-REM [nondream] sleep. You can tell a person is in REM sleep when
the bulge of his eyeballs can be seen rapidly moving under his eyelids.
Non-REM sleep can be further divided
into 4 stages. After lying down, you gently enter stage one –drowsiness or
shallow sleep. During this stage your muscles relax and your brain waves are
irregular and rapid. Its first occurrence each night typically lasts between 30
minutes and 7 minutes. When you move into stage 2 –true sleep –where you will
spend 20 percent of the night, but you are unaware of your surroundings and
cannot see even if your eyes are open.
Next come stages three and four –deeper to
deepest sleep. Here, in what is also called delta sleep, your brain produces
large, slow waves. It is now that your body is most difficult to rouse, as most
of your blood is directed to the muscles. During this time [usually about 50
percent of the night], body recovery and repair take place, and it is during
delta sleep that young bodies grow. It is important to note that anyone, young
or adult, who does not experience the deeper delta stages will likely feel
fatigued, apathetic, or even depressed the next day.
Finally, each cycle is completed by the
radically different REM stage. During this dreaming stage [typically occurring
about every 90 minutes], more blood is directed to the brain and your brain
waves are almost the same as if you were awake. However, you cannot move your muscles.
This immobility apparently keeps you from acting out dreams and hurting
yourself or others.
These REM, or dream, cycles get longer
each time they occur during the night and appear to be crucial to mental
health. In computerlike fashion, the brain sorts through short-term memory
storage, deleting unimportant data and retaining what is desired for long-term
memory. Abnormally infrequent dream cycles are known to result in emotional
difficulties. Insomniacs, for example, spend less time than average in REM
sleep, contributing to a vicious downward spiral of increasing anxiety.
So, what happens when we are regularly
deprived [voluntarily or involuntarily] of these repeated cycles, thus creating
a sleep debt? If we get fewer consecutive hours of sleep than we need, we won’t
get as much of the last and longest REM sleep period, which is vital to mental
health. If our sleep patterns become irregular, consisting of a series of naps,
we often don’t get to the deep delta sleep that is necessary to mend our
bodies. Those in serious debt suffer from shortened attention spans, memory and
vocabulary loss, a lessened ability to think analytically, and diminished
creativity.
What triggers the body to demand sleep? A
number of factors evidently combine to create a circadian [daily] rhythm, or
wake-sleep pattern. Brain chemistry appears to play a role. Also, there is a
nucleus of nerve cells located in the brain that evidently helps control the
sleep cycle. This “clock” is situated close to where the optic nerves come
together. Light thus influences how sleepy we feel. Bright light wakes you up,
while darkness induces sleep.
Your body temperature is also involved.
When your temperature is highest –typically midmorning and midevening –you are
the most alert. As your body temperature drops, you become increasingly drowsy.
Researchers agree that the pattern of wakefulness versus sleepiness varies with
individuals.
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