Unit 3

What is sleep?

a reversible behavioral state of perceptual state disengagement from and unresponsiveness to the envrionment

Why is sleep NOT just an active state?

because the brain and body cycle through different stages with varying activity

What is sleep health?

a pattern of sleep wakefulness that supports physical, mental, and social functioning

What is sleep deficiency?

a deficit in quantity or quality of sleep relative to what is needed for optimal health

What health risks are linked to poor sleep?

increased risk of mortality, heart disease, diabetes, and hypertension

What is the difference between time in bed vs actual sleep time?

time in bed = total time lying down

actual sleep time = time actaully asleep

What is the recommended sleep duration for adults?

7-9 hours

Why can sleep duration data be misleading?

studies often measure time in bed, not actual sleep time

What does SATED mean?

satisfaction

alertness

timing

efficiency

duration

What is sleep satisfaction?

subjective quality of sleep

Why is sleep satisfaction important?

linked to mental health

What is alterness?

ability to stay awake and attentive during the day

What happened with poor alertness?

increased accidents, poor academic performance, medication errors

What is sleep timing?

when you sleep within the 24 hour day

Why is inconsistent sleep timing bad?

linked to obesity and cardiometabolic issues

What is sleep efficiency?

ability to fall asleep, stay asleep, and return to sleep

What is sleep duration?

total amount of sleep (least important unless severely restricted)

What are the main sleep stages?

wake (W), NREM (N1, N2, N3), REM

What is the Typical sleep cycle order?

W → N1 → N2 → N3 → N2 → REM

How long is 1 sleep cycle?

~90 - 100 mins

How many cycles happen per night?

4-5 cycles

What are hypnic jerks?

sudden muscle movements when falling asleep

What is N1?

transition from wakefulness to light sleep

What is the hallmark of N1?

theta waves (4-7hz)

What is sleep onset latency?

time to fall asleep (W-N1)

What is good sleep onset latency?

15-30 mins

What is poor sleep onset latency?

>60min

What are the hallmarks of N2?

sleep spindles and K-complexes

What is the function of sleep spindles?

memory consolidation

What do K-complexes indicate?

some environmental awareness during sleep

What is N3?

deep sleep (slow wave sleep)

What is the hallmark of N3?

delta waves (0.5 - 2 Hz)

What happens if awakened during N3?

grogginess (sleep inertia)

What is the body state in N3?

lowest HR, BP, breathing, and movement

What happens during REM sleep?

dreaming and high brain activity

What is atonia?

muscle paralysis during REM

What happens to HR in REM?

increases to near waking levels

When is deep sleep (N3) highest?

early in the night

When is REM longest?

later sleep cycles

What is a hypnogram?

a graph showing sleep stages over time

What is polysomnography (PSG)?

gold standard sleep measurement (EEG, HR, oxygen, movement)

How do wearables estimate sleep stages?

using HR + movement (accelerometry)

How do devices identify REM sleep?

high HR + low movement

How do devices identify dep sleep?

low HR + low movement

Why is sleep duration considered less important than other SATED factors?

because quality and timing often matter more unless severely sleep deprived

Why is REM considered “deep” even with high brain activity?

because of muscle paralysis and difficulty waking

Why might someone sleep 8 hours but still feel tired?

poor sleep quality (low satisfaction or efficiency)

What are the 2 main forces that regulate sleep?

circadian rhythm and homeostatic sleep pressure

What is circadian rhythm?

a ~24 hour biological cycle driven primarily by light

What controls the circadian rhythm?

suprachiasmatic nucleus (SCN) in the hypothalamus

What is the role of the dorsomedial hypothalamic nucleus (DMH)?

integrates signals (light, food, temp., social cues) to regulate sleep-wake cycles

What is homeostatic sleep pressure?

the increasing drive to sleep the longer you are awake (sleep debt)

What molecule is associated with sleep pressure?

adenosine

How does caffeine affect sleep?

blocks adenosine receptors → reduces sleep pressure

What is the flip-flop switch model?

wake and sleep systems are mutually inhibitory, only one is active at a time

What promotes wakefulness?

dorsomedial hypothalamic nucleus (DMH) + ascending arousal system

What promotes sleep?

ventrolateral preoptic nucleus (VLPO)

Why are sleep/wake transitions abrupt?

because of the mutually inhibitory flip-flop switch

What is the protective field theory?

sleep stages exist to balance necessary sleep with environmental awareness

Why is N2 (light sleep) important in this theory?

provides awareness and ability to wake quickly

Which stages are most vulnerable?

N3 (deep sleep) and REM

What is the main idea of protective field theory?

light sleep protects deeper, necessary sleep stages

What is the energy conservation theory?

sleep reduces energy expenditure when activity is inefficient or risky

How much does metabolism decrease during sleep?

~5-15%

Why do animals sleep at specific times (day/night)?

aligns with when energy acquisition is least efficient

What is the relationship between metabolic rate and sleep duration?

higher metabolism → more sleep

What is the restorative theory?

sleep allows cellular repair and regenerration

Which stage is most important for physical recovery?

N3 (slow-wave sleep)

What hormones are active during sleep?

anabolic (growth-promoting) hormones

What happens to immune function during sleep?

it is enhanced

What happens in the brain during REM sleep (restorative view)?

neural repair and clearing of metabolic waste

Which cells clear brain waste during REM?

astrocytes and microglia

What is the memory consolidation theory?

sleep strengthens and reorganizes neural networks

Which stage is critical for memory consolidation?

N3 (slow-wave sleep) + sleep spindles

What type of memory is REM important for?

emotional memory

Why is movement suppressed during sleep?

to prevent interference with memory consolidation

Does timing of exercise affect sleep benefits?

No, benefits occur regardless of timing

What happens if you exercise < 3 hours before bed?

fall asleep faster (less N1 sleep)

What are the effects of a single bout of exercise on sleep?

inc total sleep time, inc efficiency, inc N3, dec REM

What are the effects of chronic physical activity?

better sleep quality, alertness, duration and deeper sleep

What intensity/duration gives best beneftis?

moderate-vigorous, up to ~90 mins

What is the thermogenic hypothesis?

exercise increases body temp → rapid cooling triggers sleep

Why is the thermogenic hypothesis considered weak?

benefits occur even when body temp doesn’t increase

What is the light exposure hypothesis?

exercise increases light exposure → improves circadian rhythm

What is the limitation of the light exposure theory?

no strong evidence, doesn’t explain indoor/night exercise benefits

Why does exercise improve sleep (energy theory)?

body compensates for energy expenditure by increasing sleep efficiency

Why does exercise increase deep sleep?

more tissue stress → more need for repair → more N3 sleep

Does poor sleep directly reduce performance?

not always directly

What does poor sleep affect instead?

perception of effort, attention, emotional regulation

What is the biggest risk of poor sleep in athletes?

increased injury risk

Are sleep theories mutually exclusive?

no, they all may contribute

Which stage is most important overall for health?

N3 (deep sleep)

Why does REM increase later in the night?

more neural restoration and waste clearance

Why do we feel sleepy at night?

high sleep pressure + decreasing wake signal

What is motor speed?

the time it takes to initiate and complete an intentional movement

Why is motor speed important in cognitive testing?

it determines whether someone can follow instructions, affects validity of higher cognitive tests

What is the lower limits of motor speed?

~150 ms (dominant hand)

Why does reaction time increase with complexity?

due to information processing demands, not motor speed

What is information processing?

perceiving a stimulus → interpreting → selecting action → initiating response

What are the 5 steps of information processing?

perceive

process

assign meaning

select action

respond