A01

• What are biological rhythms?

  Distinct patterns of changes in body activity that conform to cyclical time periods
• What is a circadian rhythm?

  A type of biological rhythm that recurs approximately every 24 hours, which regulates a number of body processes
• What are the 3 main body processes circadian rhythms regulate?

  1. Sleep-wake cycle

  2. Core body temperature

  3. Hormone production
• What do we mean by a 'free-running' sleep wake cycle?

  It will maintain a cycle of about 24-25 hours even in the absence of external cues
• Which research study showed support for a 'free-running' circadian rhythm?

  Michel Siffre's cave study (1962)
• Describe Michel Siffre's cave study

  - He spent several extended periods underground with no external cues to guide his rhythms

  - Found that his 'free-running' circadian rhythm was 25 hours
• How does Siffre's study show support for circadian rhythms?

  Shows that we have an internal rhythm which guides our sleep-wake cycle in the absence of external cues
• How does our circadian rhythm control release of hormones?

  - Controls release of melatonin to make us feel awake and asleep

  - During darkness - high levels of melatonin released to make us feel sleepy

  - When its light melatonin drops to wake us up
• How does our circadian rhythm control our core body temperature?

  - Drop in body temperature makes you feel sleepy (between 2 and 4pm and at 4.30am)

  - Body temperature rises towards last hours of sleep to promote alertness
• Between which times do we have our strongest dips in our sleep/wake cycle?

  Between 2 and 4am and 1 and 3pm
• What are two criteria a circadian rhythm must follow?

  1. Last 24 hours
  2. Can be reset by exposure to light and heat