endogenous pacemakers and exogenous zeitgebers

Question 1

endogenous pacemakers

Answer 1

internal body clocks that regulate many of our biological rhythms
- a second endogenous pacemaker in mammals is the pineal gland
- the pineal gland is located just behind the hypothalamus and releases melatonin in response to low light levels

Question 2

evidence supporting SCN
- DeCoursey et al (2000)

Answer 2

• 30 chipmunks had their SCN destroyed. returned to their natural habitat and observed for 80 days.
• sleep/wake cycle disappeared and a significant portion killed by predators
  —– emphasises role of the SCN in establishing and maintaining the circadian sleep/wake cycle

Question 3

evidence supporting SCN
- Ralph et al (1990)

Answer 3

• bred mutant hamsters with a 20 hour sleep cycle. SCN cells from foetal tissue of mutant hamsters were transplanted to normal hamsters, the cycle of the second group defaulted to 20 hours
  —– emphasises role of the SCN in establishing and maintaining the circadian sleep/wake cycle

Question 4

exogenous zeitgebers

Answer 4

environmental events that are responsible for entraining/regulating the biological clock of an organism

Question 5

examples of the interactions between endogenous pacemakers and exogenous

Answer 5

• jet lag: when exogenous cues are out of sync with endogenous rhythms we experience tiredness and disorientation, until internal and external signals align
• shift work: internal and external signals permanently desynchronised, leading to significant negative outcomes e.g illness, depression, divorce, premature death
• newborns: newborn babies are born without a circadian rhythm, meaning that their body is not yet trained to fall asleep regularly as adults do. it takes between 2-6 months for a baby’s circadian rhythm to be entrained

Question 6

burgess et al - using light exposure to avoid jet lag

Answer 6

volunteers participated in 1 of 3 treatments: 1) continuous bright light 2) intermittent bright light 3) dim light prior to an east -west flight
- findings:
pps - continous light - shifted their circadian rhythm by 2.1 hours
dim light by just 0.6 hours
pps in continous bright light felt sleepier 2 hours earlier in the morning (close to local time conditions)
- conclusion: light is an important zeitgeber for the SCN and entrains the circadian rhythm

Question 7

campbell and murphy

Answer 7

shone light onto the back of 15 participants knees when they woke them at various points in the night.
they managed to vary their sleep by up to three hours

Question 8

miles et al (1997)

Answer 8

recount the story of a young man, blind from birth with a circadian rhythm of 24.9 hours.
- despite exposure to social cues, his sleep wake cycle couldn’t be adjusted and consequently, he had to take sedatives at night and stimulants in the morning to keep pace with the 24 hour world