Circadian rhythms

• Circadian Rhythm

  Natural, internal process that cycles every 24 hours
• Sleep-Wake Cycle

  Recurring pattern of sleep and wakefulness

  Human sleep-wake cycle consists of 16 hrs of awake and 8 hrs of sleep
• Exogenous Zeitgebers

  External cues (light, temperature, social activities) that synchronise with the biological clock
• Endogenous Pacemakers

  Internal biological mechanisms (e.g., suprachiasmatic nucleus) that generate and regulate biological rhythms
• How we fall asleep

  1. darkness detected by the pupil
  2. sends information to SCN
  3. pineal gland secretes melatonin
  4. this makes you sleepy
• How we wake up

  1. light detected by pupil
  2. send information to SCN
  3. pineal gland stops production of melatonin
  4. this makes you wake up
• Boivin (1996)


  found that nightshift workers experience a period of reduced concentration around 6am.
• Knutson (2003)


  found that nightshift workers are three times for likely to develop heart disease