Basic Science And Sleep Knowledge Flashcards
What are the 3 distinct states of the sleep system?
Wakefulness, NREM, REM
Ascending arousal systems in the brain stem and posterior hypothalamus, what are they?
pedunculopontine (PPT) laterodorsal tegmental (LDT) locus coeruleus (LC) tuberomammillary nucleus (TMN) substantia nigra (SN) ventral tegmental (VTA) basal forebrain (BF)
Wakefulness
excitatory neurons relay sensory input to the thalamus, hypothalamus, and basal forebrain and activate cortex to increase wakefulness; suppressed during sleep.
What are the Neurotransmitters and neuropeptides that modulate and influence wakefulness promotion?
Acetylcholine Histamine Dopamine Serotonin Norepinephrine
Acetylcholine, what stages is it present?
increased in wakefulness and REM sleep
Histamine,
what stage in the sleep system is it present?
Where in the brain is it released?
What is it’s main action?
Released from tuberomammillary nucleus (posterior hypothalamus) (TMN)
increased in wakefulness and very low in REM
histamine appears to be the major arousal-promoting neurotransmitter at wake onset
Dopamine
Where in the brain is it released?
What stages in the sleep system is it increased?
What is it’s main actions?
ventral tegmental area, substantia nigra, posterior hypothalamus, and brain stem
increased in wakefulness and very low in REM
more likely to promote wakefulness under conditions of motivation or physical activity
Serotonin
What part of the brain is it released from?
What stages in the sleep system is it present?
median and dorsal raphe
increased in wakefulness and very low in REM
Norepinephrine (NE)
Where in the brain is it released?
What stages in the sleep system is it present?
What is it primary actions?
locus coeruleus (midbrain)
increased in wakefulness and very low in REM
increased cortical activation, particularly under conditions of stress and in the presence of novel stimuli
what is hypocretin (also called orexin)?
A deficiency of Orexin is associated with what condition?
What functions is orexin linked to?
Neurons in the lateral or posterior hypothalamus that produce hypocretin (also called orexin) are also active during the wake state
Orexin is a peptide that projects to cortex and subcortical arousal systems to promote awake state.
Plays important role in stabilizing wakefulness and sleep
Neuropeptide that regulates arousal, wakefulness and appetite
deficiency of hypocretin/orexin primary etiology of EDS and cataplexy in narcolepsy.
Hypocretin/orexin function linked to control of feeding behaviors, locomotion, autonomic functions.
What is the ventrolateral preoptic area (VLPO)?
major sleep-promoting area located in anterior hypothalamus
controls REM and NREM sleep
During sleep (especially SWS) – VLPO neurons active, high firing rates.
VLPO is active during sleep, releases inhibitory neurotransmitters (GABA, galanin), which inhibit neurons of ascending arousal system that are involved in wakefulness and arousal.
VLPO activated by adenosine and prostaglandin D2 (somnogens).
VLPO inhibited during awake state by NE and ACH.
VLPO neurons send projections to where?
wake-promoting regions: tuberomammillary nucleus (TMN) locus ceruleus (LC) LDT and PPT these inhibitory neurons are believed to induce sleep by coordinating the inhibition of all the wake-promoting cholinergic and aminergic regions.
Most VLPO neurons release what neurotransitters?
inhibitory neurotransmitter g-aminobutyric acid (GABA) at their sites of projection
some utilize the inhibitory neurotransmitter galanin.
What controls REM sleep?
The control of REM sleep involves the interaction of brain stem cholinergic and aminergic neurons in a complex feedback loop
neurons releasing acetylcholine (LDT/PPT region) are disinhibited by the suppression of aminergic neurons (e.g., NE, histamine) during REM.
REM-associated muscle atonia is linked to?
inhibition or loss of excitation of motor neurons in the brain stem and spinal cord via the medulla
pathways originate in the LDT and PPT
involve neurotransmitters acetylcholine, glutamate, glycine
sleep effects of drugs, overview Benzos? antihistamines? TCA's and SSRI's Psychostimulants
sleep-promoting benzos enhance GABA signaling
antihistamines block histamine receptors
TCA’s and SSRI’s act as REM suppressants enhancement of aminergic signals
inhibition of REM-promoting neurons.
Psychostimulants promote wakefulness by increasing dopamine and NE signals
Suprachiasmatic Nucleus (SCN), what is this?
Located in anterior hypothalamus, behind eyes
Major circadian pacemaker in mammals, “master clock”
Controls rhythms of CBT, sleep/wake propensity
Controls secretion of melatonin, cortisol
SCN function helps maintain alertness, alerting signal during the day, reduced signal at night
Zeitgebers entrain SCN to physical environment
Human Alertness What is the circadian dip and when does it occur? What is. The second wind phenomenon? When is the peak of alertness When is the lowest levels of alertness?
Midday decrease in alertness 2-4pm, circadian dip
Alertness peaks in early evening hours
“Second wind” right before circadian signal drops off for sleep
lowest levels of alertness occurs 4-6am
What are Zeitgebers?
Time givers (German)
External stimuli, environmental cue
Entrain the SCN to the physical environment, light-dark cycle
circadian rhythms are actually longer than 24 hrs, intrinsic clock is “entrained” by Zeitgebers
Most potent is sunlight
Other: exercise, food, social activities
In the absence of zeitgebers, circadian rhythms are desynchronized or “uncoupled” from one another “free-running”)
Other types: feeding, social, exercise, cognitive activities (work)
Circadian rhythm in humans?
Period of the rhythm is called tau
Mean value of the rhythm in humans=24.2 hrs
To maintain synchrony with light/dark cycle, external stimuli induce slight daily advance to counteract intrinsic phase delay
Zeitgebers (esp.sunlight) entrain the clock
What are markers of Circadian Phase?
CBT min (core body temp, minimum) DLMO (Dim light melatonin onset)
CBT min, when does it occur?
2-3 hrs before spontaneous awakening from unconstrained nocturnal sleep
(4-5 am in most individuals)
Reduction in CBT during sleep period corresponds to elevation in plasma melatonin
DLMO, when does it occur?
How is it measured
DLMO occurs ~2 hrs before habitual sleep onset
Determined by interval measurement of salivary or plasma melatonin performed in dim light (5 lux) in the evening
Light inhibits melatonin secretion
How to estimate CBT min?
Can be estimated as DLMO + 7 hrs
Phase Shifting by Light
Light exposure before the CBTmin causes phase delay.
Light exposure after the CBTmin causes a phase advance
Normal light exposure during early am induces daily phase advance in circadian rhythms to compensate for intrinsic tendency to phase delay due to tau longer then 24 hrs.
Common light exposures
bright blue midday sky >100,000 lux Sunrise or sunset ~10,000 lux commercial light boxes up to 10,000 lux normal room light ~200 lux moonlight 0.1 lux
What are intrinsically photosensitive retinal ganglion cells (IPRGCs) ?
circadian photoreceptors
entry point for light/dark information into the circadian system
IPRGCs send excitatory input to SCN via retiino-hypothalamic tract (RHT)
What is the retinal hypothalamic tract?
monosynaptic pathway from eye to SCN
What is an epoch
An epoch is how sleep is staged on PSG
Sleep is staged in 30 second epochs
How is stage REM detected?
EOG (eye movement) and Chin EMG are used to detect Stage R
REMs are noted
Decreased muscle tone
Decrease in chin EMG amplitude during stage R
What are the stages of sleep?
Wake, Stage W Stage N1 (light) Stage N2 (spindle, K complex) Stage N3 (SWS, Delta) Stage R (REM)
What happens without sleep?
Can’t maintain pathways in brain that let you learn and create new memories
Everyone needs sleep, but its biological purpose remains a mystery
Quality sleep is as essential to survival as food and water
What is melatonin?
Hormone that helps regulate sleep timing, “dark hormone”; need to start falling asleep
Produced in pineal gland
Inactive during the day and switches on around 9pm
Melatonin itself doesn’t make you fall asleep; it just tells your body that it’s time to fall asleep.
Lowers alertness and decreases CBT
Works in tandem with circadian clock, let’s you know when you should rest and when you should be awake.
What is the impact of light exposure on melatonin?
Too much light exposure at night; delays release of melatonin
How would you use melatonin for trouble falling asleep?
Take melatonin 5mg 60 min. Before bedtime for trouble falling asleep.
Take before usual bedtime and same time every day
What is an ultradian cycle
Sleep cycle of typically 90-100 min. In adults
Typically NREM sleep followed by period of REM sleep
Usually 3-5 NREM/REM cycles occur per night, each lasting 90-100 min.
What is sleep latency and what is normal in an adult
SL is time to fall asleep after lights out
SL should be less than 30 min, typically about 15 min.
SL increases with age slightly
Patients with sleep onsent insomnia have SL >30 min.
What is a hypnogram?
Plot of sleep stage vs time of night
What is WASO?
Wake after sleep onset
What is the typical sleep pattern for 20 year old?
Stage N1: 5% Stage N2: 45% Stage N3: 20% Stage R: 25% Arousal index (#/hr): 5-10
What is typical sleep pattern for 60 year old?
Stage N1: 15% Stage N2: 55% stage N3: 10% Stage R: 20% Arousal Index (#/hr): 15-20
How does sleep change as we age?
TST and SE decrease with age, esp after age 50
Amount of wake increases with age (WASO)
SL increases with age
When does napping stop for children?
Napping in children uncommon after age 7
Daily napping uncommon after age 5
What is the normal ultradian cycle in children?
In children, sleep cycle duration is 45-60 min.
Greater number of NREM/REM cycles per night compared to adults
How do infants enter sleep?
In infants, entry via REM sleep (active sleep) is common
How do adults enter into sleep?
Adults enter into sleep from wakefulness via NREM (usually stage N1)
What is the purpose of REM sleep?
REM sleep provides brain form of overnight therapy
Helps process difficult emotional experiences
Heightened levels of anxiety during the day can disturb sleep
What is the impact of anxiety on sleep?
Heightened levels of anxiety during the day can disturb sleep.
Anxiety prevents falling/staying asleep
Activates sympathetic nervous system, “fight or flight”
“ A ruffled mind makes a restless pillow”, C. Bronte
What is the typical sleep duration in adults?
Most of us get 7-8 hrs sleep
1/3 of population gets 6 hrs or less
Nocturia and sleep
Nocturia disrupting sleep increases with age
Increases after age 50
Impacts equally men and women
Impact of leg cramps on sleep?
Nocturnal leg cramps impact sleep
Increases after age 50
Impacts up to 5-10% of population
What is the impact of aging on sleep?
Insomnia increases with age
But getting older doesn’t necessarily mean sleeping poorly
There are accumulated health risks
What are some concerns with using meds to control insomnia?
Using medication to control insomnia symptoms provides some relief.
But sleep you get on meds is more sedation than sleep
What percent of US population has Chronic insomnia disorder?
5% or 12 million people
What is the “forbidden zone” or “second wind” ?
Relative surge of circadian based alertness to offset the buildup of sleep drive
Time zone before bedtime when it’s almost impossible to fall asleep
What is the circadian wake drive?
24 hr pattern of alertness
What is the circadian nadir and when does it occur?
Lowest period of alertness
Occurs typically at 3-5 am
What is a chronotype?
Phase preference
Propensity of individual to sleep or feel most awake at particular times in 24 hr period
What is an evening chronotype associated with?
Increased risky behaviors Depression Academic failure Obesity Metabolic dysfunction
What changes happen to sleep pattern during puberty?
All adolescents experience normal shift in circadian rhythm with age and onset of puberty.
Eveningness chronotype
Biologically based shift (delay) of up to several hrs in natural fall asleep & morning wake times
changes in sleep drive make it easier for teens to stay up later
Hard for teens to fall asleep before 11pm
How much sleep should Teens get?
Teens should ideally get ~9 hrs sleep
Insufficient sleep is very common
Teens are prone to weekend oversleep and social jet lag
What are some important environmental factors in Teen sleep?
Evening light exposure causes more phase delay
Suppresses release of melatonin
Increased sensitivity to evening light at puberty onset
What is the definition and impact of “weekend oversleep”
Practice of “making up” sleep
Marker of chronic insufficient sleep
Doesn’t reverse or compensate for impairments
What is social jet lag?
Shift in bedtime and wake times on non-school or work days Leads to “circadian misalignment” Shift melatonin onset Permanent state of jet lag Adjustment 1 day per time zone crossed
What is the impact of early school start time on Teens (before 8:30am)?
Students are required to wake for the day and function during the circadian nadir
Circadian nadir is lowest level of alertness during 24hr period
Early wake times decreases amount of REM sleep
REM sleep is critical for learning of new info and memory
Unable to meet most sleep needs (should be getting 8-10 hrs sleep)
What is an ideal start time for School for Teens?
8:30am or later school start time is considered the sleep and circadian “sweet spot” for middle schoolers and High school students
Why do we sleep?
Immune function Hormone regulation Clearing toxins from the brain Mood regulation Learning and memory Maybe be critical for prevention of AD
What is considered the optimal time to wake up?
End of REM cycle
what is melanopsin?
a photopigment sensitive to short-wave (blue-green) light
Night owl eveningness chronotype, what outcomes is it associated with?
associated with a number of adverse health, behavioral, and performance outcomes: lower physical activity depression impulsivity aggressive and antisocial behavior Substance Use disorder lower academic achievements increased perceived stress level
what is the proper dosing and timing of melatonin for Delayed Sleep phase d/o?
3 to 5 mg. Melatonin should be taken in the early evening, at least 1.5 hours before the desired bedtime.
what are assessments of Circadian/biological rhythms?
Sleep logs Actigraphy Questionnaires AM-Evening questionnaire Munich chronotype questionnaire Melatonin: Dim light melatonin onset (DLMO); Urinary 6-sulfatoxymelatonin (aMT6s) Core body temperature (CBT) PSG: not indicated
What is the pathway of melatonin synthesis?
L-tryptophan 5-hydroxytryptophan serotonin N-acetylserotonin melatonin
Melatonin is released by pineal gland
What are important characteristics of sleep homeostasis, Process S
Regulated length and depth of sleep
During each hour you are awake, somnogens build up in the brain (adenosine)
Wake-promoting substances are used up in the brain (NE, 5-HT)
During sleep somnogens are cleared and wake promoting substances are replenished
Caffeine is receptor antagonist for adenosine, i.e. alerting
What are characteristics of process S in infants and young children
Sleep pressure builds more quickly
The duration of sustained wakefulness during the day is limited
Reason for short periods of daytime sleep (naps)
What are characteristics of Circadian rhythm (process C)
Process Influences internal organization of sleep and timing and duration of daily sleep-wake cycle
24 hr in the brain
Master circadian clock = SCN (in ventral hypothalamus)
Regulate timing of appetite, urine, CBT
Circadian drive is strongest at wake time and 2 hrs after wake time
Characteristics of Process C in infants and children
Circadian timing system develops rapidly in 1st 6 months of life
Combined influence of neurodev. Maturation and social/environ. Cues (light-dark cycles)
What determines level of sleepiness in a 24 hr period?
Sleep propensity is determined by duration and quality of previous sleep
Time awake since last sleep period
What are the 2 periods of max sleepiness (circadian troughs)
3-5 pm (typically 7-9 hrs after awakening)
3-5 am
What are 2 periods of max alertness (circadian peaks)
Mid morning
Just prior to sleep onset (second wind, forbidden zone)
What is sleep inertia?
Period of incomplete arousal characterized by confusion, disorientation, cognitive slowing and irritability occurring immediately upon waking in the am or after a nap, esp. from SWS, may further compromise alertness levels
What is sleep architecture?
Structure/stages of sleep:
REM
NREM (stages 1-3)
WAke
3 distinct states each with distinct EEG, eye movements and muscle tone
What is the ultradian rhythm?f
The nocturnal cycle of sleep stages
What is the circadian rhythms?
24 hour rhythm of sleep/wakefulness and physical systems
What is sleep regulation?
Determinants of sleepiness and alertness levels
What determines our sleep patterns?
Biology Learning Maturation Culture Environment
What are characteristics of NREM stages
Slow wave sleep
Low brain activity
Brain continues to be active
Body movements are preserved
Still able to process external info and assess its salience
Resp and CV parameters are regular
After 6 mos of age, NREM divides into Stages 1, 2, 3
What are characteristics of Stage 1 sleep?
Theta waves
Sleep wake transition, “bridge” to deeper sleep
30 sec to 5 min.
Recall of fragmented visual imagery (hypnogogic hallucinations)
Brief involuntary muscle contractions (hypnic jerks)
Lowest arousal threshold
Easiest to awaken
What are characteristics of stage 2 sleep?
Sleep spindles and K Complexes
Initiation of true sleep
Bursts of rhythmic rapid EEG activity (sleep spindles; fluctuating episodes of fast activity, occurring after 4 weeks of age)
High amplitude slow-wave spikes (K complexes, first occurring at 6 months)
Lasts 5-25 min
What are characteristics of stage 3 (delta sleep)
Deepest
Slow wave sleep
Delta sleep
High voltage, low frequency activity
Respiration is slowes and most regular during SWS
Parasympathetic activity is high
Highest arousal threshold (most difficult to awaken)
Initial SWS period is about 30-45 min, followed by brief arousal (transition to wakefulness or to a lighter sleep stage
What are characteristics of REM sleep?
Active or rapid eye movement
EEG pattern: sawtooth waves
Bursts of rapid eye movements
Muscle atonia
Desynchronized cortical activity: low voltage, high freq EEG
Highest brain metabolic rate
Dreaming
Absence of skeletal muscle tone (except for diaphragm, middle ear, erectile muscles)
Lack of normal thermoregulation
Episodic bursts of phasic eye movement, hallmark of REM
What is the typical REM latency in adults?
1st REM period occurs ~70-100 min. After sleep onset
Lasts about 5 min.
What are the characteristics of REM in infant sleep?
In infants REM equals “active sleep”
Until 3 mos of age, infants enter sleep through REM
Muscle twitches and grimaces are normal
What are the characteristics of sleep cycle during the night?
Normal REM latency is 90 min.
20-25% of sleep is REM
More REM episodes as the night progresses
NREM and REM sleep alternate throught the night in cycles of ~90-110 min
Sleep cycles in infancy are 50 min and lengthen to adult level at about school age
What is the typical pattern of arousals during sleep?
Brief arousals normally followed by rapid return to sleep often occur at the end of each sleep cycle (4-6 times per night)
How does REM and NREM stages change through the night?
SWS predominates in the first 3rd of the night
REM predominates in the last 3rd
partial arousal parsomnias that occur during NREM sleep primarily occur beginning of night (sleep terrors, etc.)
REM is compromised in forced early wake times (i.e. teenagers)
What are the factors that affect the amount and timing of SWS?
Prior sleep loss
Time of sleep onset
Length of prior wakefulness
SWS is “protected” by its appearance early in noctural sleep period
SWS is preserved at expense of other sleep stages when TST is restricted
Marked increase in SWS (rebound) during night of recovery sleep following restriction
What are factors that impact REM?
Rebound phenomenon in recovery sleep
Increased arousals (osa, PLM) result in sleep fragmentation and reduced amounts of SWS, REM sleep
Increase in REM may lead to more vivid dreams
What is normal sleep architecture in newborns?
Three sleep states: REM-like, 50% of sleep Quiet (non-REM like) Indeterminate Enter sleep through active state
What is normal sleep architecture in infants (3-12 mos)
Increasing nighttime sleep compared to newborns
Amount of active/REM sleep declines
Development of 3 stages of NREM sleep at ~6 months
Sleep cycles every 50 min
Enter sleep through non-REM
Transition to 2 naps ~6 months
“Sleeping through the night” defined variably
What is normal developmental changes in sleep architecture for toddlers (1-3y)
Toddler sleep characteristics (1-3 years)
Transition to 1 nap: average ~ 18 months
Advanced circadian rhythm
High prevalence (25-30%) of bedtime problems and night wakings
REM sleep amounts continue to decline
What are Normal developmental changes in sleep architecture preschool (3-6 y)?
Preschool Sleep characteristics (3-6 years)
REM sleep amounts continue to decline Sleep cycles every 90 min High levels of SWS, peak levels Transition to no nap: 3-5 years Peak pediatric prevalence of OSA Difficulties with sleep onset and night wakings continue: 15-30%
What are Normal developmental changes in sleep architecture middle childhood (6-12 y)?
Latency from sleep onset to REM sleep increases
High sleep efficiency (time asleep/time in bed)
What are normal developmental changes in sleep architecture for teens (>12 y)?
40% decline in SWS
REM sleep at adult levels (25-30%)
Waht is normal sleep? (Normal, optimal, not disordered?)
Most people get 7-8 hrs of sleep
1/3 get 6 hrs or fewer
Insufficient sleep in areas where there are other health comorbidities
Sleep duration trends are decreasing over time, esp. since 2012
What is the most significant modern study of sleep and age?
How sleep changes over the lifespan, by Ohayon and Carskadon
Published 2004
Meta-analysis of 65 studies from 1960-2003, normal patients of all ages, looked at PSG data
What were the findings of Ohayon’s study?
TST, general decline SL: no change, slight increase SE: decline starting in middle age Stage 1%: highly variable Stage 2 %: slight increase over the lifespan (lighter sleep as people get older) REM %: decline over lifespan SWS %: decline over lifespan (young kids larger % that drop off) WASO: increase over lifespan
What are age-related changes we see with sleep?
Loss of SWS/delta sleep with aging
Teens need more sleep than adults (9-10 hrs)
Hypnogram shows more sleep consolidation in younger years
More sleep fragmentation with age
About 55% of 18 yo get 7+ hrs sleep
Long sleep more common in teens
Lowest amout of TST seen age 30-65, working age adults
Sleep apnea risks increase with age, increasing BMI
Nocturia becomes a bigger issue at age 50, men and women; related to poor sleep quality
What medical issues impact sleep quality?
OSA
Nocturia
Nocturnal leg cramps
How does nocturia impact sleep?
More time getting up to go to bathroom: results in poor sleep quality
Issue present in men and women
Inflection point at age 50
Present across the lifespan
What happens with the incidence of insomnia as we age?
The incidence of insomnia increases with age
How is sleep debt defined?
How much sleep you feel like you need vs how much sleep you get
What do we see with age and resilience to sleep loss?
2004 study showed young people dramatically underestimate how impaired they are
Older people more resilient to sleep loss
Older people overestmate how impaired they are
Younger people more likely to crash in motor vehicle stimulator after sleep restriction than older adults
How does SDB change with age?
Prevalence of SDB increases with age Plateau around age 65 Muscle fibers may be related Sleep apnea risk factors in older adults Increased risk of mortality <70, but not >70
What is prevalence of sleep disorders in older adults?
SDB =20%
Insomnia=15%
Hypersomnia=20%
How does sleep change in infancy/childhood?
Decline in avg 24hr sleep duration
Decrease in daytime napping over 1st 5 years of life
More gradual decrease in nocturnal sleep amounts into late teens
Decrease in REM %: birth =50%, early childhood into adulthood (30-35%)
40-60% decline in SWS after puberty, further decreases over the life span
High amounts of SWS in children is reason for high prevalence of partial arousal parasomnias (sleep walking and sleep terrors)
Decrease in no. Of end of cycle arousals due to lengthening of ultradian sleep cycle
Gradual shift to later bedtime and sleep onset time begins in middle childhood and accelerated in early to mid teen years
Irregularity of sleep wake patterns begins middle childhood and peaks in teen years: big differences between school night and non-school night bedtimes and wake times.
Increased weekend oversleep in teen years
What are the impacts of sleep deprivation on the brain?
Neuronal functions
Neuroplasticity: ability for brain to change structure/function in response to environment
Downscaling of synapses to compensate for net increase in synapse formation and strength during wakefulness
Gene activation/expression
Neurogenesis
Brain cell protection/ repair from stress
Neurotransmitter
Melatonin production
Cellular metabolism
Increase in stress response and stress hormones
How much do average Americans sleep?
Sleep has declined from avg of 9 hrs to 7 hrs
Americans sleep ~6hr 51 min during the week and 7hr 37 min weekends
80% of teens sleep less that optimal amounts (9+ hrs)
What are the consequences of sleep deprivation?
Reduced productivity
Lower cognitive performance
Accidents
Teens high risk for sleep related MVA’s (55% of fall asleep MVAs)
24 hrs of sleep deprivation impairs performance as much as 0.10 blood ETOH level
What is Maggie’s law?
Law in NJ, passed 1997
If you are a motorist who has been up for 24+ hours, fall asleep and kill another driver: you can be charged with vehicular homicide
What are long term consequences of sleep deprivation?
Increased risk of obesity Hypertension Diabetes Mortality (too little or too much=bad) Changes in waking activity
How is social jet lag defined?
What is its impact?
Weekend oversleep Adjustment takes 1 day per time zone crossed Effects persist up to 3 days Associated daytime sleepiness Poor academic performance Depressed mood
Development of circadian rhythms
Term: sleep-wake periods occur randomly
1 month: CBT has circadian rhythm
3 months: Hormones (melatonin and cortisol) begin to cycle in circadian rhythm
3-6 months: maturation of circadian system leads to sleep consolidation (sleeping through the night)
Nap patterns in children: summary
Transitions:
to 2 naps: ~6 mos
to one nap: ~ 18 mos
To no nap: ~ 3-5 years
High normative variability in timing of transitions
Transitions often happen gradually rather than abruptly, and can temporarily disrupt nighttime sleep routine
What is the impact of sleep duration on health?
Short sleep duration (6 hours or less per 24-hour period) is associated with adverse outcomes, including mortality
Long sleep duration (>9 to 10 hours per 24-hour period) may also be associated with adverse health outcomes
At a population level, the optimal sleep duration in adults for good health is 7 to 9 hours, although individual variability exists
