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the daytime. As a
result, replication
was relegated to
the dark, and a basic pattern of day/night cycle was engrained
within the cell and passed down to subsequent generations. At
some time in the distant past, the days may have been longer,
because when we are deprived of time clues, we gravitate toward
a 25-hour circadian cycle.
The Internal Works of Our Biological Watch
In your brain, there is a type of “pacemaker” located within the
suprachiasmatic nuclei. This area regulates the firing of nerve
cells that seem to control your circadian rhythm. Scientists
can’t explain precisely how this area in your brain “keeps time.”
They do know your brain relies on “outside” influences called
zeitgebers (German for time givers) to keep it on a normal
schedule.
The most obvious zeitgeber is daylight. When daylight hits your
eyes, cells in the retinas signal your brain. Other zeitgebers are
ambient temperature, sleep, social contact, physical activity,
and even regular meal times. They all send “timekeeping” clues
to your brain, helping keep your circadian rhythm running on
schedule.
Circadian Rhythm
Disruption
Any time that our normal
25-hour circadian rhythm
is altered or interrupted,
it will have physiological
and behavioral impacts.
This is better known as
circadian rhythm disruption, or CRD. Normal circadian rhythms
are naturally altered as one ages including changes in sleep
pattern with respect to earlier onset of sleepiness, early-morning
awakenings, and increased need for daytime napping.
Sleep Disorders and CRD
Several chronic sleep disorders can lead or contribute to
circadian rhythm disruptions, including:
• Delayed Sleep Phase Syndrome. This disorder causes
a delay in the normal sleep onset time by two or more
hours. People affected by this disorder complain of
late-evening insomnia and/or excessive early-morning
sleepiness, have difficulties falling asleep before 2:00 a.m.,
have short sleep periods during weekdays, and prolonged
(9-12 hours) sleep periods during the weekends. These
individuals tend to experience depression and other
psychiatric disorders.
• Advanced Sleep Phase Syndrome. This is a disorder
where sleepiness occurs well before the desired sleep
schedule. The resulting symptoms include evening
sleepiness, an early sleep onset, and an morning
awakening that is earlier than desired. A person feels
the urge to go to sleep between 6:00 and 8:00 p.m. and
wakes up between 1:00 and 3:00 a.m. the following
morning. This disorder can have a negative impact on
an individual’s personal
or social life because
of the need to leave
early-evening social
activities to sleep.
Evening sleepiness may
also represent a driving
hazard.
• Non 24-Hour Sleep-
Wake Disorder. This
disorder is the result of
an inadvertent delay of
the sleep onset time,
followed by unsuccessful
attempts to sleep at the
desired sleep schedule.
People affected by this disorder constantly delay sleep
onset times that interfere with circadian rhythms. They
have a normal sleep duration pattern but live in a freerunning
“biological clock” of 25 hours instead of the
community-accepted 24-hour clock. The sleep cycle is
affected by inconsistent insomnia that occurs at different
times. Those affected will sometimes fall asleep at a later
time and wake up later; or fall asleep at an earlier time
and wake up earlier.
Even if you do not have a chronic sleep disorder, there are
several measures that can help you get a good night’s sleep.
Among these are:
• Mental or physical relaxation techniques (reading,
meditation, yoga).
• If you don’t fall a sleep within 30 minutes of going to bed,
get out of bed and try an activity that helps induce sleep
such as reading, listening to relaxing music, watching
something boring on TV, etc.
• Ensure you are in an environment conducive to sleeping
(dark, quiet, comfortable temperature and mattress).
• Exercise regularly, but not too near bedtime.
• A nutritious, balanced diet.
Jet lag is more evident if you
fly from west to east because
it is more difficult for your
body to adjust to “losing time”
when you journey east than to
“gaining time,” when you fly
from east to west.
Tips to Help Minimize
Jet Lag
➢ Adjust your bedtime by an hour a day a few days before
your trip. This will adjust your sleep pattern to match the
　
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