Chapter 5
Section 2: The Rhythms of Sleep
Why Do We sleep?
• The exact function is still uncertain.
• Sleep appears to provide a time for
rejuvenation and repairs.
–Eliminate waste products from muscles,
repair cells, strengthen the immune
system, & recover abilities lost during the
day
• When we do not sleep, our bodies operate
abnormally and we lose mental function
• Sleep deprivation for 4 or more days
becomes uncomfortable & soon
unbearable
–Can lead to infection & death
• Necessary for normal mental functioning
–In chronic sleep deprivation, high
levels of cortisol may damage or
impair the brain cells that are
necessary for learning & memory
–May even begin to have hallucinations
& delusions
Sleep Disorders
• At least 40 million Americans suffer
from chronic, long-term sleep
disorders each year
• These disorders interfere with work,
driving, & social activities
• Insomnia- difficulty falling or staying
asleep
–Resulting from worry & anxiety, hot
flashes, arthritis
• Sleep apnea- caused from blockage of
air passages to failure of the brain to
control respiration correctly
–Can lead to high blood pressure &
irregular heartbeat
Sleep walking
• Characterized by walking or some activity
while sleeping
• REM disorder
• Difficult to wake during
an episode
• Can be caused by fatigue,
stress, or anxiety
• Narcolepsy- daytime attacks of
sleepiness lasting 5 to 30 minutes
• Causes of sleepiness
–Staying up late & not allowing
for enough sleep
Nightmares
• Stressful things that happen during
the day can turn dreams into
nightmares.
• Nightmares may be a way to relieve
the pressures of the day.
How much sleep do I need?
• Infants- 16 hours
• Teenagers- 9 hours
• Adults- 7-8 hours
–Some can function on 5 others
need 10
• When people are sleepy, traffic & work
accidents are more likely
• 2/3 of Americans get fewer than the
recommended 8 hours
–Lack of sleep has been linked to lower
grades
The Realms of Sleep
• Until the early 1950s, little was known
about the physiology of sleep.
• Then a breakthrough occurred in the lab of
physiologist Nathaniel Kleitman, who
identified REM sleep.
• The research led to our understanding of
the stages of sleep.
• Cycle that recurs every 90 minutes
–REM average 20 minutes
• Cycle
–Alpha waves- regular, slow rhythm & a
high amplitude, eventually slow down
& you drift off
Physiological/
Psychological Changes
Awake, but Body is relaxed
Sleep
Stages
Drowsy
Stage 1
(5%)
Stage 2
(44-55%)
Heart rate slower, light sleep
(1 & 2 last 30 min)
Person may talk in their sleep
Stages of Sleep
Stage 1.
Your brain waves
become small and
irregular, & you feel
yourself drifting on
the edge of
consciousness, in a
state of light sleep.
If awakened, you may
recall fantasies or a
few visual images.
Stage 2.
Your brain emits
occasional short
bursts of rapid,
high-peaking
waves called sleep
spindles.
Minor noises
probably won't
disturb you.
Stage 3
Deep sleep, somewhat difficult
to awaken
Stage 4
(1523%)
REM
(2025%)
Considerable movement, most
difficult to awaken
90 min. into sleep cycle, return
to stage 1 & begin REM sleep;
appear paralyzed, recall
dreams when awakened
Stage 3.
In addition to the waves
characteristic of Stage
2, your brain
occasionally emits
delta waves, very slow
waves with very high
peaks.
Your breathing & pulse
have slowed down,
your muscles are
relaxed, & you are
hard to arouse.
Stage 4.
Delta waves have
taken over, & you
are in deep sleep.
It will probably take
vigorous shaking or
a loud noise to
awaken you.
If you talk or walk in
your sleep, this is
when you are likely
to do so.
• Sequence takes about 30-45 minutes & then
goes in reverse
–About 70-90 minutes into sleep in stage 1,
brain emits long bursts of rapid irregular
waves, heart rate increases, blood pressure
rises, & breathing becomes faster &
irregular
• Twitches may occur in your face &
fingers, skeletal muscles go limp (REM)
• Most likely to dream
• REM & non-REM sleep continue to
alternate throughout the night with
stages 3 & 4 becoming shorter &
tend to disappear
–Varies from person to person