Features of Sleep (OCR GCSE Psychology): Revision Note

Stages of sleep

• Sleep follows a repeating cycle of five stages, lasting around 90 minutes

• Throughout the night, we move through these stages multiple times

Stage 1: light sleep

• Brain waves slow down: alpha waves become theta waves

  • Alpha and theta are types of brain waves

  • Alpha waves help us calm down

  • Theta waves promote deeper relaxation

• People drift in and out of sleep, are drowsy and easy to wake

• Eyes move slowly, and muscle spasms or the sensation of falling are common

• Makes up around 5-10% of sleep

Stage 2: onset of sleep

• Theta waves continue to slow with occasional bursts of rapid brain waves

• Eye movement stops; heart rate and temperature drop

• Conscious awareness of the outside world fades

• Makes up about 45-50% of adult sleep

Stages 3 and 4: deep sleep (slow-wave sleep)

• Stage 3:

  • There is a mix of slow delta waves with some faster waves

    • Delta waves are the slowest brain waves, most prominent during deep

• Stage 4:

  • The brain produces only delta waves

  • It is hard to wake someone from deep sleep

  • There is no eye movement and reduced muscle activity

  • Growth hormone is released for physical repair

  • The body carries out immune system strengthening

  • Makes up about 20-25% of adult sleep

Stage 5: REM Sleep (rapid eye movement)

• Brain waves are fast and resemble wakefulness

• Eyes move rapidly and limbs are temporarily paralysed

• Heart rate increases; breathing becomes quicker and irregular

• Most vivid dreams occur here

• People experience 3-5 intervals of REM sleep each night

• REM periods get longer as the night progresses

• Makes up about 20-25% of adult sleep

Endogenous pacemakers (EPs) & exogenous zeitgebers (EZs)

• Our 24-hour sleep–wake cycle is regulated by both:

  • endogenous pacemakers: internal biological clocks

  • exogenous zeitgebers: external cues (e.g., light)

• They interact to keep our circadian rhythm stable

Endogenous pacemakers

• These are internal body clocks that regulate or control biological rhythms

• A key factor in how we sleep is exposure to light or darkness

• The key pacemaker is known as the Suprachiasmatic Nucleus (SCN)

Suprachiasmatic nucleus (SCN)

• The SCN is a part of the brain that regulates circadian rhythms

• It is located in the hypothalamus

• It receives information about light via the optic nerve

• The SCN sends signals to other parts of the brain that regulate:

  • hormone release, i.e. melatonin

  • body temperature

  • alertness/tiredness

Pineal gland

• The pineal gland is a small endocrine gland found in the brain

• It is activated by the SCN when it gets dark

• The pineal gland produces and releases melatonin

Melatonin

• Melatonin is a natural hormone linked to sleep onset

  • Levels rise in the evening, making us sleepy

  • They remain high for about 12 hours through the night

  • Melatonin drops to very low levels during the day

  • This hormone helps regulate the circadian rhythm

• Melatonin production can be disrupted by:

  • shift work

  • screen use at night

  • jet lag/time zone changes

Exogenous zeitgebers

• Exogenous zeitgebers are external cues that influence the sleep–wake cycle

• The main zeitgeber is light

  • Light resets the SCN each day

  • Darkness triggers melatonin release (promotes sleep)

  • Light suppresses melatonin, which makes us more alert

• Other zeitgebers include:

  • social cues (noise, activity)

  • temperature

  • mealtimes