Biological Rhythms

Question 1

What are the three classifications of biological rhythms?

Answer 1

1) Circadian rhythms - cycles that generally occur once every 24 hours, e.g. sleep-wake cycle,
2) Infradian rhythms - cycles that occur less than once every day, e.g. menstrual cycle,
3) Ultradian rhythms - cycles that occur more than once every 24 hours, e.g. sleep cycle has several repeating stages of light and deep sleep.

Question 2

What are endogenous pacemakers?

Answer 2

• Biological, internal, influences on biological rhythms, e.g.:
  1) Some aspects of our biological rhythms are set by genetically determined structures and mechanisms within the body,
  2) The suprachiasmatic nucleus, part of the hypothalamus, seems to act as an internal clock to keept the body on an approximate 24-hour sleep-waking cycle,
  3) It is sensitive to light and regulates the pineal gland, which secretes melatonin.

Question 3

What are exogenous zeitgebers?

Answer 3

• Influences from outside the body that act like a prompt, which may trigger a biological rhythm, e.g. light.

Question 4

Siffre (1975), method and findings

Answer 4

• Spent six months in a cave, he had no clocks and no natural light,
• His sleep schedule extended from 24 hours to a 25-30 hour cycle,
• Seems that natural light is needed to fine-tune our normal 24-hour cycle.