A01

• What are the two main factors governing biological rhythms?

  Endogenous pacemakers and exogenous zeitgebers
• What are ultradian rhythms?

  Rhythms that occur multiple times a day
• What are infradian rhythms?

  Rhythms that take longer than a day
• What are circannual rhythms?

  Rhythms that last much longer than a day
• How long do circadian rhythms last?

  Around 24 hours
• What is the role of daylight in the sleep/wake cycle?

  It acts as an important exogenous zeitgeber
• What is the internal pacemaker that governs the sleep/wake cycle?

  The suprachiasmatic nucleus (SCN)
• Where is the SCN located?

  Above the optic chiasm
• How can exogenous zeitgebers affect the SCN?

  They can reset the SCN
• What does 'free-running' refer to in biological rhythms?

  Biological rhythms without external stimuli
• Who conducted a cave study to investigate biological rhythms?

  Michel Siffre
• What did Siffre believe after spending two months in a cave?

  It was mid-August
• What was the duration of Siffre's second cave study?

  Six months
• What was the typical length of Siffre's free-running biological rhythm?

  About 25 hours
• What did the bunker study by Aschoff and Wever reveal?

  Circadian rhythms were between 24 and 25 hours
• What do Siffre's and Aschoff's studies suggest about the natural sleep/wake cycle?

  It may be slightly longer than 24 hours
• What did Folkard's study demonstrate about exogenous zeitgebers?

  They cannot easily override internal rhythms
• How long did participants live in the dark cave during Folkard's study?

  Three weeks
• What was the result of speeding up the clock in Folkard's study?

  Only one participant adjusted comfortably
• What does Folkard's study suggest about the strength of circadian rhythms?

  They are strong and resistant to change