BIOPSYCHOLOGY - endogenous pacemakers and exogenous zeitgebers

Question 1

what are endogenous pacemakers?

Answer 1

internal body clocks that regulate many of our biological rhythms, such as the influence of the SCN on the sleep/wake cycle.

Question 2

outline DeCoursey et al (2000).

Answer 2

• destroyed SCN connections in the brains of 30 chipmunks
• chipmunks were returned to their natural habitats
• observed for 80 days

Question 3

what are the findings of Decoursey et al?

Answer 3

• sleep/wake cycle of chipmunks disappeared by end of study = significant proportion had been killed by predators
• they were awake at a time where they were vulnerable to attack

Question 4

outline Ralph et al (1990).

Answer 4

• bred mutant hamsters with a 20hr sleep cycle.
• when SCN from the foetal tissue of mutant hamsters were transplanted to brains of normal hamsters = second group defaulted to 20 hours

Question 5

How does the SCN and pineal gland work together?

Answer 5

• SCN passes info on day length and light to pineal gland.
• pineal gland = another endogenous mechanism guiding the sleep/wake cycle.
• at night = pineal gland increases melatonin which induces sleep

Question 6

what are exogenous zeitgebers?

Answer 6

external factors in the environment that reset out biological clocks through the process of entrainment

Question 7

what is the most dominant zeitgebers and how does it work?

Answer 7

light
- receptors in the SCN are sensitive to light
- light maintains the sleep/wake cycle
- light has indirect influence on key processes such as hormone secretion and blood circulation

Question 8

Outline Campbell and Murphy (1988).

Answer 8

15 ps were woken at various times and a light pas was shone on the back of their knees
- there was a deviation in the sleep wake cycle
= suggests that light is a POWERFUL EXOGENOUS ZEITGEBER = doesn’t rely on the eyes to exert its influence on the brain

Question 9

what are social cues?

Answer 9

another type of exogenous zeitgeber.
eg mealtimes and bed times
- jet lag = local times of eating snd sleeping is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances.

Question 10

evaluate research on the SCN.

Answer 10

• SCN research can conceal other body clocks
  = there are numerous circadian rhythms in cells of lungs,pancreas,skin. They act independently.
  Damiola et al (2000) = changing feeding patterns in mice could alter the circadian rhythms of cells in the liver while leaving the rhythm of the SCN UNAFFECTED.
• endogenous pacemakers cannot be studied in isolation
  eg isolation studies such as Siffres cave study is rare.
• Siffre made use of artificial light = however in everyday life, pacemakers and zeitgebers such as natural light interact. It doesn’t make sense to separate the two for the purpose of research.

+ Mammalian brains have similar structures, therefore findings from animal studies can be generalised

• unethical = animals in Decoursey et al study were exposed to risk when returned to their natural habitat and most died as a result.

Question 11

evaluate research on exogenous zeitgebers and endogenous pacemakers.

Answer 11

• exogenous zeitgebers do not have the same effect in all environments
  eg people who live within the Arctic circle have similar sleep patterns all year around despite spending 6 months in almost total darkness. = this suggests that sleep/wake cycle is controlled by endogenous pacemakers that can override environmental changes in light.
• evidence challenges the role of exogenous zeitgebers.
  eg Miles et al = studied a blind young man who had an abnormal circadian rhythm of 24.9 hours. despite exposure to social cues eg mealtimes , his sleep wake cycle could not be adjusted. = social cues alone is not effective in resetting the biological rhythm.

+ research suggests that exogenous factors may be more responsible for the changes in sleep amongst older people. Hood et al (2004) found that insomnia can be managed by being more active and having more exposure to light.