Body Rhythms
&
Sleep
Biological Rhythms
• Natural variations we experience daily in our psychological and physiological
functioning
• Fall into three main categories
• Circadian Rhythms
• Ultradian Rhythms
• Infradian Rhythms
Circadian Rhythms
• Any rhythmic change that occurs approximately once in a 24-hour
cycle
• Responsible for our arousal levels throughout the day.
• Many of your processes like blood pressure, hormones, pain sensitivity
along with sleep and wake cycles vary over the day
• If time, watch the Cave
Experiment from The
Brain: Module 13 (6 min)
• In the absence of time
cues, the cycle period
will become somewhat
longer than 24 hours
The Body’s Clock
• Suprachiasmatic
nucleus (SCN)
— cluster of
neurons in the
hypothalamus
that governs the
timing of
circadian
rhythms
• Melatonin —
hormone of the
pineal gland that
produces
sleepiness
The Body’s Clock: How it works
• Special photoreceptors in the retina regulate the
effects of light on the body’s circadian rhythms
• In response to morning light, signals from these
special photoreceptors are relayed via the optic
nerve to the suprachiasmatic nucleus.
• In turn, the suprachiasmatic nucleus causes the
pineal gland to reduce the production of melatonin, a
hormone that causes sleepiness.
• As blood levels of melatonin decrease, mental
alertness increases.
• Daily exposure to bright light, especially sunlight,
helps keep the body’s circadian rhythms
synchronized and operating on a 24-hour schedule.
How Melatonin works:
• More melatonin = sleepy and reduce activity levels
– highest levels between 1-3 AM
• Less Melatonin = more alert and active
– Body stops produced melatonin shortly before sunrise and
sunlight suppresses melatonin levels throughout the day
• Jet Lag – Since your body is still operating on the time
you left from, your melatonin levels will be off causing
a disruption in your circadian rhythms and making you
mentally fatigued, depressed, irritable and have
problems sleeping.
• Night workers will always have some problems due to
sunlight resetting their biological clock.
Biological Rhythms
• Play “Can You Beat Jet Lag?” (6:44) (Start at 16:00).
• Segment #15 from Scientific American
Frontiers: Video Collection for
Introductory Psychology (2nd edition)
• How light is used by the body to “reset”
your biological clock.
Not a Morning
Person?
• Sleep Inertia - feeling of grogginess or impaired mental
ability immediately following an abrupt awakening
• Staying in bed until the last possible moment will only intensify
disorientation as you hustle to work.
• Staying in bed until the last possible moment will only intensify
disorientation as you hustle to work.
• Best way to treat it is to allow for more passage of time.
– Set your alarm 15 minutes earlier and make it so you have to get
up to turn it off.
• Drink something with caffeine and sit near sunlight.
• Read something or do meditation to get your brain engaged.
Ultradian Rhythms
• Biological rhythms that occur more than once
each day
• Example: Cycling through the stages of sleep
throughout the night, appetite
Infradian Rhythms
• Biological rhythms that occur once a month or once a
season
• These rhythms are infrequent
• Example:
– Women’s menstrual cycle
– bear’s winter hibernation
The Stages of Sleep
Why do We Sleep?
• Restoration theory—body wears out during the day
and sleep is necessary to put it back in shape
– NREM sleep sees increases in the release of growth hormone,
testosterone, prolactin.
– REM sleep plays a role in rate of brain development that occurs in the
early stages of the lifespan.
– Allows neurons to repair themselves while pruning unused connections
– Sleep consolidates memories – strengthening neural connections
– Allows us to be better problem solvers the next day
• Adaptive theory—sleep emerged in evolution to
preserve energy and protect during the time of day
when there is little value and considerable danger
– Animals with few natural predators sleep the most while animals with
many sleep less.
– Hibernation occurs during the time of year most hazardous to the animal.
Electroencephalograph (EEG)
• A machine that amplifies and records waves of
electrical activity that sweep across the brain’s
surface
• Electrodes are placed on the person’s scalp to
measure the waves
• Used as a means to measure the stages of sleep
Electroencephalogram (EEG)
• Electrodes placed on the scalp provide a record of the
electrical activity of the brain
• EEG recordings are a rough index of psychological states
EEG Waves of Wakefulness
Beta Waves:
Awake & attentive
low amplitude
fast, irregular
Alpha Waves:
Awake but non-attentive
Larger amplitude
Onset of Sleep
• Awake & alert, your brain produces small, fast brain
waves called beta waves.
• As you lay down and close your eyes, your brain's
electrical activity gradually gears down generating
slightly larger and slower alpha brain waves.
• During drowsy, presleep stage you may experience
vivid sensory phenomena called hypnagogic
hallucinations.
• Most common hallucination is that of falling which
can produce a myoclonic jerk or sleep starts –
involuntary muscle spasm of the whole body that jolts
the person completely awake.
Stage 1 Sleep
• Breathing is slowed.
• Brain waves become irregular.
• It is easy to wake the person, who will
insist they are not asleep.
• Lasts only a few minutes.
• Familiar sounds fade away but your can
regain alertness if something interrupts
you.
• Some imagery is common although no
very strange or vivid.
Stages of Sleep
Stage 1
Stage 1
Stage 2 Sleep
• Brain wave cycle slows.
• Appearance of sleep spindles or brief
bursts of brain activity and K complexes
or large high-voltage spikes of brain
activity that periodically occur.
• Brain activity slows considerably and breathing becomes rhythmic.
• Slight muscle twitches occur.
• Brain waves begin to slowly switch from Theta waves to slower
and larger delta waves.
Stage 2
K Complex
Stages 3 and 4 Sleep
“Slow Wave Sleep”
• Increase in delta waves (large & slow waves per second)
– 20% = Stage 3. More than 50% = Stage 4.
• First time through stage 4 is about 30 minutes and is where one gets
rejuvenated
• During the first stage 4 of sleep, heart rate, blood pressure and
breathing drop to their lowest levels and it is very hard to wake up.
• Sleepwalking occurs here.
• People can "wake up" during stage 4 and do a simple task and not
remember it.
Stage 4
Stages of Sleep1-4
Quick Review
• Sleep stage 1: brief
transition stage when first
falling asleep
• Stages 2 through 4 (slowwave sleep): successively
deeper stages of sleep
• Slow Wave 3 & 4:
Characterized by an
increasing percentage
of slow, irregular, highamplitude delta waves
Sleep stage 1
1 second
Sleep stage 2
Spindlers (bursts of activity)
Sleep stage 4
Delta waves
REM Sleep
• N-REM (non-REM sleep) = Stages 1 - 4
• REM Sleep - Rapid eye movement as eyes
move quickly back and forth
• Most dreaming occurs in REM
– muscle activity is suppressed to keep you acting
them out.
• REM Rebound - If denied REM sleep and then
allowed a person will “Catch Up” on REM
sleep and will increase their time in REM by
50%.
REM Sleep
REM: Paradoxical Sleep
• One’s physiology is close to that of being awake but the brainstem
blocks all muscle movement
• Brain wave patterns are similar to when a person is awake
• Visual and motor neurons in the brain fire like they do when you are
awake.
• Eyes dart back and forth and heart rate, blood pressure and respirations
fluctuate up and down.
• The first REM cycle lasts for 5 to 15 minutes. Each one gets longer as
night goes on.
Stages of Sleep
• Upon reaching stage 4 and after about 80 to 100 minutes of
total sleep time, sleep lightens, returns through stages 3 and
2
• REM sleep emerges, characterized by EEG patterns that
resemble beta waves of alert wakefulness
– muscles most relaxed
– rapid eye movements occur
– dreams occur
• Four or five sleep cycles occur in a typical night’s
sleep; less time is spent in slow-wave, more is spent in REM
Typical Night’s Sleep
Sleep Changes
through Life
Sleep Review
• Play “Sleep: Brain Functions” (11:12)
– Module #14 from The Brain: Teaching Modules
(2nd edition).
• Review of the stages of sleep.
• What happens to animals that are not
allowed to sleep?
• What defines normal & abnormal sleep?
• Categories of Sleep Disorders