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Sleep, Screenshot 2025-10-15 at 12.14.39 pm - Coggle Diagram
Sleep
Why do we sleep?
Inactivity theory: keeps us safe from predators and accidents that could happen in the dark.
- Weird theory, considering you’re unresponsive and can’t defend yourself from predators.
- Predators sleep longer than prey > sleep is not protective
Energy conservation theory: reduce energy use
- Metabolism is reduced by ~10%.
Brain plasticity theory > sleep promotes brain plasticity (changes in brain structure, neural organisation, and connectivity)
- Important in brain development > babies sleep a LOT, especially since so much of it is REM.
- Memory, creativity, reaction times, concentration, sustained attention, planning, reasoning, learning and decision-making are all impaired due to a lack of sleep
Restoration theory restores what we lose or use while awake
- Repairs: muscle growth, tissue repair, protein synthesis, and growth hormone release all happen to a larger extent during sleep compared to awake
- Housekeeping > evidence of a removal of neurotoxic waste in rats
- Evidence: Sleep deprivation can cause illness and death.
- 11-32 days of deprivation to cause death in rats
- Humans do not die from short-term sleep deprivation > sleep overrides actions, and you’ll go to sleep unintentionally.
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What is sleep?
Sleep is a reversible behavioural state of perceptual disengagement from and unresponsiveness to the environment.
Stages of sleep
- Four distinct stages
- NREM > non-rapid eye movement > dreamless
- REM > rapid-eyemovement > dreaming
- Different brain waves, breathing and muscle tension changes, other bodily changes.
Light sleep
- ~45-55% of total sleep
- Heart rate decreases
- Body temperature decreases
- Other metabolic functions slow
- Sleep spindles
Slow wave sleep
- Brain waves slow down and become larger
- Relaxed muscles
- Sleep through most disturbances
- More memory consolidation
Sleep onset
- ~5-10 minutes
- Drifting off but easily woken
- Muscles relaxed
- Blood pressure decreases
- Brain temperature decreases
REM sleep
- Dream sleep
- ~20-25% total sleep
- Eye muscles move rapidly (most others are paralysed)
- Brain activity is fast and random
- Increased and irregular heart rate and breathing
- REM rebound > if a person is woken during REM sleep one night, the next night a larger percentage of their sleep will be REM sleep to catch up.
Stages of healthy sleep
- 3 and 4 are both slow-wave sleep
- Most likely does not occur under general anaesthesia
- Takes about an hour and a half to get through one sleep cycle > from light to REM
- More deep sleep happens early at night
REM sleep takes up more of each sleep cycle towards the morning. > usually, the dreams you remember
How much sleep?
- Babies need 16-18 hours, of which about 50% is REM
- Toddlers need ~9.5 hours
- School-age children need 7-9 hours
- And older people ned 7-8 hours, but often get less.
- Sleep really messes up as a result of hormones > one of the first signs of perimenopause.
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