Sleep: Slep Stages and Theories 1.5b

  • humans have around a 16-hour day before laying down to recharge

  • even when you’re asleep, your perceptual window is open a crack

    • meaning you process most info outside your conscious awareness

      • Ex: you move around in bed without falling off

Biological Rhythms and Sleep

  • life has rhythmic tides

Circadian Rhythm

Circadian Rhythm: our biological clock; regular bodily rhythms that occur on a 24-hour cycle

  • our bodies roughly synchronize with the 24-hour cycle of day and night thanks to our internal biological clock

  • age and experience can alter our circadian rhythm

    • as we get older, we’re no longer able to stay up in the early hours of the day

Sleep Stages

REM Sleep: rapid eye movement sleep; vivid dreams occur. Also known as paradoxical sleep because muscles are relaxed but other body systems are active

  • the sleeping brain remains active and has its own biological rhythm

  • every 90 minutes, you cycle through sleep stages

  • jerky eye movements were accompanied by energetic brain activity

  • yawning stretches your neck muscles and increases heart rate, which increases alertness

  • researchers use electrodes to detect brain waves during sleep

  • in stage 1 of sleep, you may experience sensory images without a sensory stimulus (hallucinations)

    • lasts up to 5 minutes

    • sensation of falling/floating

      • also known as hypnagogic sensations: bizarre experiences while transition to sleep

  • Stage 2 of sleep: contains periodic sleep spindles—bursts of rapid, rhythmic brain wave activity that aid memory processing

    • lasts up to 15-20 min

    • could still be awakened easily but you are clearly asleep

  • Stage 3: brain emits large, slow delta waves

    • lasts up to 30 min

    • hard to awaken

    • children may wet the bed at this stage

REM Sleep

  • about an hour after you first fall asleep, you return to stage 2

    • in stage 2 you spend half your night there

  • stage 2 is where you have REM

  • during REM, heart rate increases, breathing is rapid and irregular, and every half-minute your eyes dart around in momentarily bursts of activity

    • the eye movements announce that you are dreaming (usually emotional)

  • REM sleep tricks your brain that the dreams are real

  • genitals become aroused during REM

    • erection or lubrication, regardless of a sexual dream

    • morning erection stems from the might’s last REM period, often just before waking

  • during REM, your brain’s motor cortex is active, but the brainstem blocks its messages

    • causes the body to relax (this immobility may linger after REM sleep, causing sleep paralysis)

  • for younger adults, they experience 90-minute cycles, older adults have shorter more frequent cycles

  • as the night wears on, stage 3 grows shorter and disappears

    • causes stage 2 periods to be longer

What Affects Our Sleep Patterns

  • newborns sleep two-thirds of the day; adults sleep one-third

  • sleep patterns are genetically, socially, culturally, and economically influenced

  • Superchiasmatic Nucleus (SCN): pair of cell clusters in the hypthalamus that controls circadian rhythm. In response to light, the SCN adjusts melatonin production, thus modifying our feelings of sleepiness

    • bright light affects our sleepiness by activating light-sensitive retinal proteins; this signals the SCN to decrease production of melatonin

  • Being deprived of llight disrupts our circadian rhythm

  • desynchronization causes fatigue, stomach issues, heart diseases, and breast cancer

Why Do We Sleep?

  • Sleep protects

    • a species’ sleep pattern tends to suit its ecological niche

    • Ex: ancestors would sleep in dark caves to protect themselves from being seen

  • Sleep restores

    • sleep gives resting neurons time to repair themselves, while weakening unused connections

  • Sleep aids memory consolidation

    • helps restore and rebuild our fading memories of the day’s experiences

      • memories are consolidated during slow-wave deep sleep

      • reactivates recent experiences stored in the hippocampus and moves them to permanent storage elsewhere in the cortex

  • Sleep feeds creative thinking

    • dreams can inspire noteworthy achievements

    • after working on a task, then sleeping on it, people solve difficult problems more insightfully than those awake

  • Sleep supports growth

    • during slow-wave sleep, pituary gland releases human growth hormones

  • Sleep conserves energy

  • Sleep improves athletic ability

    • REM sleep and Stage 2 sleep help strengthen neural connections like muscle memory