10
Biological Rhythms
and Sleep
10 Biological Rhythms and Sleep: Part I
Biological Rhythms
• Many Animals Show Daily Rhythms in Activity
• The Hypothalamus Houses an Endogenous Circadian
Clock
10 Biological Rhythms and Sleep: Part II
Sleeping and Waking
• Human Sleep Exhibits Different Stages
• Our Sleep Patterns Change across the Life Span
• Manipulating Sleep Reveals an Underlying Structure
• What are the Biological Functions of Sleep?
• At Least Four Interacting Neural Systems Underlie Sleep
• Sleep Disorders Can Be Serious, Even Life-Threatening
10 Many Animals Show Daily Rhythms in Activity
Biological rhythms are regular fluctuations in a living
process
• Circadian rhythms have a rhythm of about 24 hours
• Ultradian rhythms such as bouts of activity, feeding,
and hormone release repeat more than once a day
• Infradian rhythms such as body weight and
reproductive cycles repeat less than once a day
10 Many Animals Show Daily Rhythms in Activity
Diurnal—active during the light
Nocturnal—active during the dark
Circadian rhythms are generated by an endogenous
(internal) clock
10 Many Animals Show Daily Rhythms in Activity
A free-running animal is maintaining its own cycle with no
external cues, such as light
The period, or time between successive cycles, may not
be exactly 24 hours
Figure 10.2 How Activity Rhythms Are Measured (Part 1)
10 Many Animals Show Daily Rhythms in Activity
A phase shift is the shift in activity in response to a
synchronizing stimulus, such as light or food
Entrainment is the process of shifting the rhythm
The cue that an animal uses to synchronize with the
environment is called a zeitgeber or “time-giver”
Figure 10.2 How Activity Rhythms Are Measured (Part 2)
10 The Hypothalamus Houses an Endogenous Circadian Clock
The biological clock is located in the suprachiasmatic
nucleus (SCN)—above the optic chiasm in the
hypothalamus
Studies in SCN-lesioned animals showed disrupted
circadian rhythms
Isolated SCN cells maintain electrical activity synchronized
to the previous light cycle
Figure 10.3 The Effects of Lesions in the SCN
10 The Hypothalamus Houses an Endogenous Circadian Clock
Transplant studies proved that the SCN produces a
circadian rhythm
Hamsters with SCN lesions received a SCN tissue
transplant from hamsters with a very short period, ~20
hours
Circadian rhythms were restored but matched the shorter
period of the donor
Figure 10.5 Brain Transplants Prove That the SCN Contains a Clock
10 The Hypothalamus Houses an Endogenous Circadian Clock
Circadian rhythms entrain to light-dark cycles using
different pathways, some outside of the eye
The pineal gland in amphibians and birds is sensitive to
light
Melatonin is secreted to inform the brain about light
10 The Hypothalamus Houses an Endogenous Circadian Clock
In mammals, light information goes from the eye to the
SCN via the retinohypothalamic pathway
Some retinal ganglion cells project to the SCN
Most contain melanopsin, a special photopigment, that
makes them sensitive to light
Figure 10.6 Components of a Circadian System
10 The Hypothalamus Houses an Endogenous Circadian Clock
Molecular studies in Drosophila using mutations of the
period gene helped to understand the circadian clock in
mammals
SCN cells in mammals make two proteins:
• Clock
• Cycle
10 The Hypothalamus Houses an Endogenous Circadian Clock
Clock and Cycle proteins bind together to form a dimer
The Clock/Cycle dimer promotes transcription of two
genes:
• Period (per)
• Cryptochrome (cry)
10 The Hypothalamus Houses an Endogenous Circadian Clock
Per and Cry proteins bind to each other and also to Tau
The Per/Cry/Tau protein complex enters the nucleus and
inhibits the transcription of per and cry
No new proteins are made until the first set degrades
The cycle repeats ~every 24 hours
Figure 10.7 A Molecular Clock in Flies and Mice
10 The Hypothalamus Houses an Endogenous Circadian Clock
Gene mutations show how important the clock is to
behavior in constant conditions:
• In tau mutations the period is shorter than normal
• Double Clock mutants—severely arrhythmic
Figure 10.8 When the Endogenous Clock Goes Kaput
10 The Hypothalamus Houses an Endogenous Circadian Clock
Sleep is synchronized to external events, including light
and dark
Stimuli like lights, food, jobs, and alarm clocks entrain us to
be awake or to sleep
In the absence of cues, humans have a free-running period
of approximately 25 hours
Figure 10.9 Humans Free-Run Too
10 Human Sleep Exhibits Different Stages
Electrical brain potentials can be used to classify levels of
arousal and states of sleep
Electroencephalography (EEG) records electrical activity
in the brain
10 Human Sleep Exhibits Different Stages
Two distinct classes of sleep:
• Slow-wave sleep (SWS) can be divided into four
stages and is characterized by slow-wave EEG activity
• Rapid-eye-movement sleep (REM) is characterized
by small amplitude, fast-EEG waves, no postural
tension, and rapid eye movements
10 Human Sleep Exhibits Different Stages
The pattern of activity in an awake person contains many
frequencies:
• Dominated by waves of fast frequency and low
amplitude (15 to 20 Hz)
• Known as beta activity or desynchronized EEG
Alpha rhythm occurs in relaxation, a regular oscillation of
8 to 12 Hz
Figure 10.10 Electrophysiological Correlates of Sleep and Waking
10 Human Sleep Exhibits Different Stages
Four stages of slow-wave sleep:
• Stage 1 sleep
o
Shows events of irregular frequency and smaller
amplitude, as well as vertex spikes, or sharp waves
o
Heart rate slows, muscle tension reduces, eyes
move about
o
Lasts several minutes
10 Human Sleep Exhibits Different Stages
• Stage 2 sleep
o
Defined by waves of 12 to 14 Hz that occur in
bursts, called sleep spindles
o
K-complexes appear–sharp negative EEG
potentials
10 Human Sleep Exhibits Different Stages
• Early stage 3 sleep
o
Continued sleep spindles as in stage 2
o
Defined by the appearance of large-amplitude, very
slow waves called delta waves
o
Delta waves occur about once per second
10 Human Sleep Exhibits Different Stages
• Late stage 3 sleep
o
Delta waves are present about half the time
10 Human Sleep Exhibits Different Stages
REM sleep follows SWS
• Active EEG with small-amplitude, high-frequency
waves, like an awake person
• Muscles are relaxed—called paradoxical sleep
10 Human Sleep Exhibits Different Stages
In a typical night of young adult sleep:
• Sleep time ranges from 7–8 hours
• 45–50% is stage 2 sleep, 20% is REM sleep
• Cycles last 90–110 minutes, but cycles early in the
night have more stage 3 SWS, and later cycles have
more REM sleep
Figure 10.11 A Typical Night of Sleep in a Young Adult
10 Human Sleep Exhibits Different Stages
At puberty, most people shift their circadian rhythm of sleep
so that they get up later in the day
However, most high schools require adolescents to arrive
even earlier
Later starts improved attendance and enrollment, and
reduced depression and in-class sleeping
Figure 10.12 How I Hate to Get Out of Bed in the Morning!
10 Human Sleep Exhibits Different Stages
Vivid dreams occur during REM sleep, characterized by:
• Visual imagery
• Sense that the dreamer is “there”
Nightmares are frightening dreams that awaken the
sleeper from REM sleep
Night terrors are sudden arousals from stage 3 SWS,
marked by fear and autonomic activity
10 Human Sleep Exhibits Different Stages
REM sleep evolved in some vertebrates:
• Nearly all mammals display both REM and SWS
• Birds also display both REM and SWS sleep
10 Human Sleep Exhibits Different Stages
Dolphins do not show REM sleep, perhaps because
relaxed muscles are incompatible with the need to come
to the surface to breathe
In dolphins and birds, only one brain hemisphere enters
SWS at a time—the other remains awake
Figure 10.14 Sleep in Marine Mammals
10 Our Sleep Patterns Change across the Life Span
Mammals sleep more during infancy than in adulthood
Infant sleep is characterized by:
• Shorter sleep cycles
• More REM sleep—50%, which may provide essential
stimulation to the developing nervous system
Figure 10.15 The Trouble with Babies
Figure 10.16 Human Sleep Patterns Change with Age
10 Our Sleep Patterns Change across the Life Span
As people age, total time asleep declines, and times
awakened increase
The biggest loss is time spent in stage 3:
• At age 60, only half as much time is spent as at age 20
• By age 90, stage 3 has disappeared
Figure 10.17 The Typical Pattern of Sleep in an Elderly Person
10 Manipulating Sleep Reveals an Underlying Structure
Effects of sleep deprivation—the partial or total prevention
of sleep:
• Increased irritability
• Difficulty in concentrating
• Episodes of disorientation
Effects can vary with age and other factors
Figure 10.18 I Need Sleep!
10 Manipulating Sleep Reveals an Underlying Structure
Sleep recovery is the process of sleeping more than
normally, after a period of deprivation
• Night 1—stage 3 sleep is increased, but stage 2 is
decreased
• Night 2—most recovery of REM sleep, which is more
intense than normal with more rapid eye movements
Figure 10.19 Sleep Recovery after 11 Days Awake
10 Manipulating Sleep Reveals an Underlying Structure
Sleep deprivation can be fatal
• Total sleep deprivation compromises the immune
system and leads to death
• The disease fatal familial insomnia is inherited—in
midlife people stop sleeping and die 7–24 months after
onset of the insomnia
10 What Are the Biological Functions of Sleep?
Four functions of sleep:
• Energy conservation
• Niche adaptation
• Body restoration
• Memory consolidation
14 What Are the Biological Functions of Sleep?
One role of sleep is to conserve energy
• Muscular tension, heart rate, blood pressure,
temperature, and rate of respiration are reduced
10 What Are the Biological Functions of Sleep?
Sleep helps animals avoid predators—animals sleep during
the part of the day when they are most vulnerable
The ecological niche for each species is the unique
assortment of opportunities and challenges in its
environment
Figure 10.20 Sleep Helps Animals to Adapt an Ecological Niche
10 What Are the Biological Functions of Sleep?
Sleep restores the body by replenishing metabolic
requirements, such as proteins
Most growth hormone is only released during SWS
Proper sleep is essential for immune function
10 What Are the Biological Functions of Sleep?
Sleep may aid memory consolidation:
• Sleep during the interval between learning and recall
may reduce interfering stimuli
• Memory typically decays and sleep may slow this down
• Or sleep, especially REM, may actively contribute
through processes that consolidate the learned
material
10 What Are the Biological Functions of Sleep?
A challenge to sleep theories is the existence of a few
people who hardly sleep at all yet are normal and healthy
Whatever the function of sleep, these people fill it with a
brief nap
Figure 10.21 A Nonsleeper
10 At Least Four Interacting Neural Systems Underlie Sleep
Sleep is an active state mediated by:
• A forebrain system—displays SWS
• A brainstem system—activates the forebrain
• A pontine system—triggers REM sleep
• A hypothalamic system—affects the other three
10 At Least Four Interacting Neural Systems Underlie Sleep
Transection experiments showed that different sleep
systems originate in different parts of the brain
• The isolated brain is made by an incision between the
medulla and the spinal cord
o
Animals showed signs of sleep and wakefulness,
proving that the networks reside in the brain
Figure 10.22 Transecting the Brain at Different Levels (Part 2)
10 At Least Four Interacting Neural Systems Underlie Sleep
• An isolated forebrain is made by an incision in the
midbrain
o
The electrical activity in the forebrain showed
constant SWS, but not REM—thus, the forebrain
alone can generate SWS
Figure 10.22 Transecting the Brain at Different Levels (Part 3)
10 At Least Four Interacting Neural Systems Underlie Sleep
The constant SWS activity in the forebrain is generated by
the basal forebrain, a ventral region
Neurons in this region become active at sleep onset and
release GABA
• GABA activates receptors in the nearby
tuberomamillary nucleus
• GABA receptors are also stimulated by general
anesthetics to produce slow waves resembling SWS
10 At Least Four Interacting Neural Systems Underlie Sleep
The reticular formation is able to activate the cortex
• Electrical stimulation of this area will wake up sleeping
animals
• Lesions of this area promote sleep
The forebrain and reticular formation seem to guide the
brain between SWS and wakefulness
Figure 10.23 Brain Mechanisms Underlying Sleep
10 At Least Four Interacting Neural Systems Underlie Sleep
An area of the pons, near the locus coeruleus, is
responsible for REM sleep
Some neurons in this region are only active during REM
sleep
They inhibit motoneurons to keep them from firing,
disabling the motor system during REM sleep
Figure 10.24 Acting Out a Dream
10 At Least Four Interacting Neural Systems Underlie Sleep
The study of narcolepsy revealed the hypothalamic sleep
center.
Narcolepsy sufferers:
• Have frequent sleep attacks and excessive daytime
sleepiness
• Do not go through SWS before REM sleep
• May show cataplexy—a sudden loss of muscle tone,
leading to collapse
14 At Least Four Interacting Neural Systems Underlie Sleep
Narcoleptic dogs have a mutant gene for a hypocretin
receptor
• Hypocretin normally prevents the transition from
wakefulness directly into REM sleep
• Interfering with hypocretin signaling leads to
narcolepsy
Figure 10.25 Canine Narcolepsy
10 At Least Four Interacting Neural Systems Underlie Sleep
Hypocretin neurons in the hypothalamus project to other
sleep system centers: the basal forebrain, the reticular
formation, and the locus coeruleus
Axons also go to the tuberomamillary nucleus, whose
inhibition induces SWS
The hypothalamus seems to contain a hypocretin sleep
that controls wakefulness, SWS sleep, or REM sleep
Figure 10.26 Neural Degeneration in Humans with Narcolepsy
10 At Least Four Interacting Neural Systems Underlie Sleep
Sleep paralysis is the brief inability to move just before
falling asleep, or just after waking up
It may be caused by the pontine center continuing to signal
for muscle relaxation, even when awake
10 Sleep Disorders Can Be Serious, Even Life-Threatening
Sleep disorders in children:
• Night terrors and sleep enuresis (bed-wetting) are
associated with SWS
• Somnambulism (sleepwalking) occurs during stage 3
SWS, and may persist into adulthood
14 Sleep Disorders Can Be Serious, Even Life-Threatening
REM behavior disorder (RBD) is characterized by
organized behavior, from an asleep person
• It usually begins after age 50 and may be followed by
beginning symptoms of Parkinson’s disease
• This suggests damage in the brain motor systems
10 Sleep Disorders Can Be Serious, Even Life-Threatening
Sleep-onset insomnia is a difficulty in falling asleep, and
can be caused by situational factors, such as shift work or
jet lag
Sleep-maintenance insomnia is a difficulty in staying
asleep and may be caused by drugs or neurological
factors
10 Sleep Disorders Can Be Serious, Even Life-Threatening
In sleep apnea, breathing may stop or slow down when
muscles in the chest and diaphragm relax too much or
respiratory neurons in the brain stem don’t signal properly
• Sleep apnea may be accompanied by snoring
Sleep state misperception occurs when people report
insomnia even when they were asleep
10 Sleep Disorders Can Be Serious, Even Life-Threatening
Sudden infant death syndrome (SIDS) is sleep apnea
resulting from immature respiratory pacemaker systems
or arousal mechanisms
Putting babies to sleep on their backs can prevent
suffocation due to apnea
Photo, p. 297 Back to Sleep
10 Sleep Disorders Can Be Serious, Even Life-Threatening
Most sleeping pills bind to GABA receptors throughout the
brain.
Continued use of sleeping pills:
• Makes them ineffective
• Produces marked changes in sleep patterns that
persist even when not taking the drug
• Can lead to drowsiness and memory gaps