● Sleep restores homeostasis disrupted during

wakefulness.
Chapter 14 ● Functions include:
Sleep, Dreaming, And Circadian ○ Repairing the body (e.g., muscle
recovery, immune system support).
Rhythms ○ Clearing waste products from the brain.
○ Restoring energy levels.
○ Facilitating memory consolidation and
STAGES OF SLEEP emotional regulation.

Sleep progresses through a series of stages categorized as 2. Adaptation Theories

non-REM (NREM) sleep and REM sleep, each serving
distinct physiological and cognitive functions.
● Sleep evolved to enhance survival:
○ Energy conservation during periods
Non-REM Sleep when activity is less productive or safe
(e.g., nighttime for humans).
1. Stage 1 (Light Sleep): ○ Protecting individuals from predators or
○ Transition from wakefulness to sleep. environmental hazards.
○ EEG: Low-voltage, high-frequency
waves. These theories suggest that while the body and brain benefit
○ Characteristics: Relaxed muscles, slow from sleep, its patterns and timing have also evolved as a
eye movements, and easily awakened. survival strategy.
2. Stage 2:
○ EEG: Presence of sleep spindles (brief
bursts of high-frequency waves) and Why Do We Sleep When We Do?
K-complexes (large waveforms in
response to stimuli). 1. Circadian Rhythms:
○ Characteristics: No eye movement, ○ Internal biological clocks regulate
reduced heart rate, and deeper sleep-wake cycles, roughly aligning with
relaxation. the 24-hour light-dark cycle.
3. Stage 3 (Slow-Wave Sleep or Deep Sleep): ○ Controlled by the suprachiasmatic
○ EEG: Dominated by delta waves (slow, nucleus (SCN) in the hypothalamus,
high-amplitude waves). which responds to light cues.
○ Characteristics: Deep restorative sleep; 2. Environmental Influences:
difficult to wake. Critical for physical ○ Zeitgebers (time givers): External cues
recovery and memory consolidation. like sunlight, meals, and social activities
help synchronize circadian rhythms.
REM Sleep ○ Disruptions (e.g., jet lag or shift work) can
lead to sleep disorders and health
issues.
● Rapid Eye Movement (REM) Sleep: 3. Sleep Pressure:
○ EEG: Low-amplitude, high-frequency ○ Homeostatic Drive: The longer one
waves similar to wakefulness. stays awake, the stronger the urge to
○ Characteristics: Rapid eye movements, sleep due to a buildup of sleep-inducing
muscle atonia (paralysis), vivid dreaming, chemicals like adenosine.
and high brain activity.
○ Function: Associated with emotional
processing, memory consolidation, and
creative problem-solving.
Effects of Sleep Deprivation
Sleep Cycle
Sleep deprivation affects the body and mind, with both
● A typical sleep cycle lasts ~90 minutes, cycling short-term and long-term consequences. The impact can vary
through NREM stages followed by REM. depending on the duration and the specific stages of sleep
● Order: Stage 1 → Stage 2 → Stage 3 → REM → missed.
Repeat.
● Deep sleep predominates early in the night, while Short-Term Effects
REM periods become longer toward morning.
1. Cognitive Impairment:
○ Reduced attention, focus, and
decision-making ability.
Why Do We Sleep, and Why Do We Sleep When ○ Slower reaction times and increased risk
of errors.
We Do? Sleep is essential for survival, but its purpose
○ Memory problems, particularly with
has been debated. Two primary theories explain why we
learning and recall.
sleep:
2. Mood Changes:
1. Recuperation Theories ○ Irritability, stress, and increased
emotional sensitivity.
 ○ Heightened risk of anxiety and ○ Governed by the suprachiasmatic
depression with prolonged deprivation. nucleus (SCN) in the hypothalamus,
3. Physical Effects: which acts as the body’s "master clock."
○ Increased fatigue and decreased 2. Regulation:
physical performance. ○ The SCN receives light signals through
○ Impaired immune function, making the the eyes and adjusts bodily functions like
body more susceptible to infections. hormone release, body temperature, and
sleep-wake timing.
Long-Term Effects
Free-Running Cycles
1. Health Risks:
○ Increased risk of chronic ● When external cues (light, meals) are absent, the
○ conditions such as heart disease, body’s natural rhythm typically follows a slightly
diabetes, and obesity. longer cycle (~24.2 hours).
○ Hormonal imbalances affecting appetite, ● Experiments in isolation show people maintain a
growth, and stress response. rhythm even without external stimuli, indicating the
2. Mental Health Decline: role of internal biological clocks.
○ Persistent sleep deprivation can
contribute to depression, anxiety, and Role of Zeitgebers (Time Givers)
even psychosis in extreme cases.
3. Decreased Sleep Efficiency:
● Zeitgebers are external cues that synchronize the
○ Chronic deprivation disrupts sleep
body’s internal clock to the environment. Examples
architecture, reducing the quality of
include:
restorative sleep.
○ Light: The primary regulator of circadian
rhythms.
Notable Cases ○ Meals: Meal timing influences energy
regulation.
● Randy Gardner (1964): Stayed awake for 11 days: ○ Social Activities: Work and social
○ Experienced mood swings, schedules impact sleep timing.
hallucinations, and cognitive decline.
○ Fully recovered after normal sleep. Disruptions to Circadian Rhythms
● Experimental Findings:
○ Deprivation of REM sleep leads to REM
1. Jet Lag:
rebound, where REM sleep is prioritized
○ Caused by rapid travel across time
in subsequent sleep cycles.
zones, disrupting the internal clock.
○ Prolonged deprivation of slow-wave
○ Symptoms: Fatigue, insomnia, poor
sleep (SWS) impacts physical recovery
concentration, and digestive issues.
and immune function.
○ Coping strategies: Gradual adjustment to
local time, light exposure, and melatonin
Sleep Deprivation in Animals supplements.
2. Shift Work:
● Animal studies show severe effects, including ○ Working at odd hours (night shifts)
metabolic failure and death, with extreme misaligns the body’s clock with
deprivation. environmental cues.
○ Long-term effects: Increased risk of
Key Takeaways sleep disorders, cardiovascular issues,
and mood disturbances.
● Sleep deprivation impacts nearly every system in
the body. Health Implications of Disrupted Cycles
● Recovery is possible with adequate sleep,
emphasizing the importance of prioritizing regular, ● Chronic misalignment of circadian rhythms can
high-quality sleep. lead to:
○ Sleep disorders like insomnia.
○ Impaired cognitive and physical
performance.
○ Higher risk for chronic conditions (e.g.,
diabetes, heart disease).
Circadian Sleep Cycles Circadian sleep cycles are the
natural 24-hour rhythms that regulate sleep and wakefulness. Tips for Maintaining Healthy Circadian Rhythms
These cycles are influenced by internal biological clocks and
external environmental factors. 1. Keep a consistent sleep schedule.
Key Concepts 2. Maximize natural light exposure during the day.
3. Avoid screens and bright light before bedtime.
1. Circadian Rhythms: 4. Create a dark, quiet sleep environment.
○ Internal cycles that align with the Earth's
24-hour light-dark cycle.
Four Areas In The Brain Involved In Sleep ● Studies show exogenous melatonin (melatonin
taken as a supplement) has a small effect on
Two Areas of the Hypothalamus Involved in Sleep helping people fall asleep.

● Anterior hypothalamus, basal-forebrain area (sleep) Sleep Disorders

● Posterior hypothalamus, midbrain area
(wakefulness) ● Insomnia: Trouble falling or staying asleep.
● Hypersomnia: Feeling excessively sleepy or
Reticular Formation and Sleep sleeping too much.
● REM-Sleep Disorders: Problems specifically tied to
● a network of neurons in the brainstem—was the REM stage of sleep, like disruptions in
identified as the area responsible for controlling dreaming or muscle activity.
wakefulness. It helps the brain stay alert and
regulates the transition between sleep and Insomia
wakefulness.
● Iatrogenic Insomnia: Sleeping pills can worsen
Reticular REM-Sleep Nuclei insomnia due to tolerance and withdrawal
symptoms.
● Sleep (including REM sleep) is controlled by a ● Insomnia vs. Sleep Quality: People may think they
network of brain areas, not just one. These areas have insomnia, but they might just have interrupted
can work together—or sometimes sleep or poor quality sleep.
independently—which helps explain why behaviors ● Sleep Apnea: Breathing stops during sleep,
don’t fit neatly into single categories. causing poor sleep quality and daytime sleepiness.
It’s more common in men, overweight people, and
the elderly.
Drugs that affect sleep - Most drugs that ● Leg Issues: Disorders like periodic limb movement
influence sleep fall into two different classes: and restless legs can disrupt sleep, but have no
hypnotic and antihypnotic. Hypnotic drugs are perfect treatments.
drugs that increase sleep; antihypnotic drugs are ● Sleep Restriction Therapy: Limiting time in bed
and gradually increasing it can help insomniacs
drugs that reduce sleep. A third class of improve their sleep.
sleep-influencing drugs comprises those that
influence its circadian rhythmicity; the main drug Hypersomnia
of this class is melatonin
● Daytime sleepiness with sudden, brief sleep
Hypnotic drugs
episodes.

● Benzodiazepines ● Cataplexy: Sudden loss of muscle control, leading

- Benzodiazepines (like diazepam and clonazepam) to collapse.
are medications that make people sleepy and help ● Sleep paralysis: Inability to move when falling
them fall asleep faster. They also reduce nighttime asleep or waking up.
awakenings and increase total sleep time. ● Hypnagogic hallucinations: Dream-like
● Imidazopyridines
experiences while awake.
● 5- hydroxytryptophan (5-HTP)

REM Sleep Abnormality: Narcoleptics often enter REM

Anti Hypnotic Drugs
sleep immediately upon falling asleep and
experience REM features (like muscle paralysis)
Antihypnotic drugs are substances that keep you awake. while awake.
There are three main types:
Cause: The disorder is linked to a lack of orexin (a
1. Cocaine-based stimulants. neuropeptide for wakefulness), possibly due to an
2. Amphetamine-based stimulants. autoimmune response that destroys
3. Tricyclic antidepressants. orexin-producing neurons in the hypothalamus.

Melatonin Treatment:

What is Melatonin? ● Stimulants (e.g., amphetamines) help with

wakefulness but have side effects.
● Modafinil is a newer, less addictive treatment.
● Melatonin is a hormone made in the brain’s pineal ● Antidepressants can help with cataplexy.
gland using serotonin.
● The pineal gland is a tiny structure near the middle
of the brain.
● Melatonin levels go up at night and are linked to
darkness and sleep.
 might be more efficient, as naps have significant
REM-Sleep–Related Disorders restorative benefits.

● REM-Sleep-Related Disorders: Some sleep Effects of Shorter Sleep Times on Health

disorders are specifically linked to REM sleep,
including narcolepsy. ● For years, 8 hours of sleep per night was
● Lack of REM Sleep: Rare cases show people who considered ideal for health and longevity, but large
function well without REM sleep, even after brain studies from the U.S. and Japan have challenged
injury affecting REM controllers. this belief. These studies, which focused on healthy
● REM-Sleep Behavior Disorder: People with this individuals and excluded those who slept less due
disorder experience REM sleep without muscle to illness or stress, found that people who slept
paralysis, leading to acting out dreams. It is often between 5 and 7 hours per night had the fewest
seen in Parkinson's disease and may result from deaths, while those who slept 8 hours had more
damage to the nucleus magnocellularis, which health issues. While these studies don’t prove that
controls muscle relaxation during REM sleep. 8 hours of sleep causes health problems, they
suggest that sleeping less than 8 hours isn’t as
Effects on Long term sleep disorder - Research harmful as once believed. Additionally, people in
pre-industrial hunter-gatherer societies, who sleep
comparing short and long sleepers suggests
less than 8 hours, tend to have fewer health issues
that sleep loss may not cause major problems, and better physical fitness.
and the brain can adjust. However, studies on
sleep duration and health show mixed results, Long-Term Sleep Reduction: A Personal Case Study
with surprising findings about the effects of
reduced sleep. ● The author, JP, experimented with reducing sleep
to 5 hours per night for four weeks. The benefits
included gaining extra waking hours and avoiding
daily activities like traffic. However, sleepiness was
Difference between short and long sleepers
a challenge, especially before bed. Despite this,
the author found that most people can manage
● A 2004 study by Fichten and colleagues compared with 5.5 hours of sleep without major issues,
short sleepers (6 hours or less) and long sleepers aligning with expert recommendations. After
(8 hours or more) using a large sample of healthy considering polyphasic sleep (multiple naps), the
adults. The study measured 48 factors, including author revised the estimate downward, suggesting
sleepiness, stress, anxiety, and life satisfaction. The even less sleep might be viable for some,
main finding was that the only difference between emphasizing that shorter sleep could work for
short and long sleepers was the amount of sleep active individuals who adapt over time.
they got—short sleepers didn’t show any signs of
negative effects from their shorter sleep, unless
they were also under stress. The study concluded
that sleep duration alone doesn't seem to affect
health, as long as people sleep the amount they
feel is right for them.

Long-Term reduction of nightly sleep

● Two studies explored whether healthy people can

adapt to sleeping less. In one study, volunteers
reduced their sleep to 5.5 hours per night for 60
days, with only a slight decrease in vigilance. In
another study, volunteers gradually reduced their
sleep over several months, reaching as low as 4.5
hours per night. While participants did experience
some daytime sleepiness at very low sleep
durations, there were no major negative effects on
mood, health, or performance. After one year, all
participants were sleeping less than before the
study, but without excessive sleepiness. This
suggests that it’s possible for people to adapt to a
shorter sleep schedule.

Long-Term Sleep Reduction by Napping

● Humans typically sleep once a day (monophasic

sleep), but they do experience periods of
sleepiness during the day, especially in the late
morning and afternoon. Some research suggests
polyphasic sleep (sleeping multiple times per day)