Sleep

• Purpose of sleep


  Restorative function and evolutionary enhancement of survival
• Survival theories of sleep

  • Enhances survival by protecting organisms during risky times
  • Conserves energy after survival functions are fulfilled
  • Protects from harm or death
• Research evidence for survival theories comes from studies on behaviour patterns and sleep-wake cycles of different species
• Animals with few predators


  • Lions sleep as much as 15 hours a day
• Humans sleep at night because we are highly visual and need light to find food
• During most of our evolution, we would be tucked away in a cave protecting ourselves from predators and the cold nights
• Restorative theories


  Propose that sleep allows the body to replenish energy and recover from depleting activities
• Restorative functions of sleep

  • Repairs damaged cells
  • Detoxifies muscles
  • Replenishes energy
• People usually sleep for longer periods when they are sick
• Growth hormones


  Promote repair at a higher rate during sleep than when awake
• Studies involving sleep-deprived rats have shown that prolonged sleep deprivation results in breakdown of bodily tissues and death within 3 weeks
• NREM sleep


  • Important for restoring and repairing the body
• REM sleep


  • Restores the brain and higher mental functions
  • Consolidates memory of newly learned information
• REM is much more abundant in the developing fetus and infants compared to childhood and later stages of development
• REM sleep maintains brain circuits between groups of neurons
• Psychologists have found that if a person is woken up several times during REM sleep they will eventually spend more time in the REM stage when they have uninterrupted sleep
• Sleep-Wake Cycle


  Experience two types of sleep: NREM and REM in a continuous cycle
• In adults, one cycle of NREM sleep lasts about 70-90 minutes
• NREM sleep


  • Approximately 80% of our sleep time is spent in NREM
  • Typically the first half of the night has more NREM sleep than the second half
• NREM Stage one


  Drift in and out of true sleep state
• NREM Stage two


  Light stage of sleep
• NREM Stage three


  Start of the deepest period of sleep
• NREM Stage four


  Very deep sleep
• REM sleep


  • Period of rapid eye movement
  • Brainwave pattern is irregular
  • Body appears calm and inactive
• Most dreaming occurs during REM sleep
• Dreaming also occurs in NREM sleep but is less vivid and fragmented
• Length and repetition of the sleep cycle involves continuous passing through NREM and REM sleep cycles
• Sleep deprivation is defined as going without sleep
• Effects of sleep deprivation

  • Mood
  • Attention
  • Reflex speed
  • Vision
• Chronic sleep deprivation involves not having any sleep at all
• Partial sleep loss over relatively short periods has temporary and relatively minor effects
• Prolonged sleep deprivation can lead to significant psychological effects such as anxiety disorders and hallucinations
• Sleep deprivation can lead to hypertension, diabetes, obesity, and acceleration of aging
• A lack of sleep can make it more difficult for the body to process sugar
• Sleep deprivation can create an imbalance in the hormones that regulate appetite
• Microsleep lasts for a very brief period and the individual has no recollection of it
• People who get 7-8 hours of sleep at night tend to outlive those who are chronically deprived
• Shift work involves hours of paid employment outside the normal working day
• Sleep can make it more difficult for the body to process sugar, contributing to glucose intolerance
• Sleep deprivation


  Creates an imbalance in the hormones that regulate appetite