Circadian Rhythm and Sleep: Quick Reference

Consciousness: awareness of internal and external stimuli.
Internal stimuli: pain, hunger, thirst, sleepiness, thoughts, emotions.
External stimuli: light, warmth, sounds, presence of others.
Consciousness is a continuum from full awareness to deep sleep; many states exist beyond just wakeful vs. asleep (e.g., daydreaming, intoxication, anesthesia).
Daydreaming can occur during activities (e.g., driving) while not fully aware of the ongoing task.

Biological rhythms: internal rhythms of biological activity.
Examples: menstrual cycle (~ $28$ days), body temperature fluctuations (~ $24$ hours).
Circadian rhythm: biological rhythm about $24$ hours, linked to the light-dark cycle.
Sleep-wake cycle is a prominent circadian rhythm; other rhythms include heart rate, blood pressure, blood sugar, and body temperature.
Temperature and alertness: higher body temperature associated with alertness; lower temperature associated with sleepiness.

Brain clock resides in the hypothalamus, in an area called the suprachiasmatic nucleus (SCN).
Light information from retina to SCN synchronizes internal clock with outside world.
This wiring allows circadian rhythms to align with environmental light cues.

Melatonin: hormone regulated by the pineal gland; released in darkness, inhibited by light; helps regulate sleep and biological rhythms.
Chronotype: individual differences in circadian timing (e.g., morning larks vs night owls).
Chronotype affects sleep regulation and preferred activity times.

Jet lag: mismatch between internal circadian cycles and environment after rapid time-zone changes; symptoms include fatigue, sluggishness, irritability, insomnia.
Rotating shift work: schedules that change from early to late shifts, disrupting normal circadian rhythm.
Consequences: sleep problems, depression/anxiety, relationship strain, reduced performance, fatigue.
Coping strategies: strategic use of bright light during wake times and darkness when not working to realign the clock.

Bright light exposure can help realign circadian clocks during shifts or jet lag.
Light-driven clock means exposure to bright light during work shifts and dark exposure when not working can alleviate insomnia and anxiety/depression symptoms.

Sleep debt: accumulating lack of sufficient sleep; leads to decreased alertness and cognitive efficiency.
Modern lighting and activity patterns have reduced average sleep time.
National Sleep Foundation (2015 update) provides sleep duration recommendations by age.

Sleep debt and deprivation have significant negative psychological and physiological consequences.
Lack of sleep reduces mental alertness and cognitive function; can be linked to depression-like symptoms.
Sleep deprivation is associated with obesity, high blood pressure, elevated stress hormones, and reduced immune function.
Sleep-deprived individuals may fall asleep more quickly; staying awake for long periods impairs functioning.
Severe effects occur after long wakefulness: staying awake > $24$ hours worsens deficits; staying awake for $48$ hours can lead to hallucinations.
Some effects are more pronounced after repeated nights with少 than $4$ hours in bed.

Sleep needs vary across the lifespan; newborns require the most sleep, infants sleep a lot, and sleep decreases with age.
By age $65$ , many adults average fewer than $7$ hours of sleep per day (night).

Circadian rhythms are the body's 24-hour cycles synchronized by light.
The SCN and melatonin are central to sleep-wake regulation.
Jet lag and shift work disrupt circadian alignment; light exposure can help realign.
Sleep debt has broad negative effects on health and performance; sleep needs are highest in infancy and decline with age, with a common benchmark of around $7 ext{--}9$ hours for adults.