Endogenous pacemakers and exogenous zeitgebers

Question 1

What is the suprachiasmatic nucleus (SCN)?

Answer 1

-Main endogenous pacemaker: influential in maintaining sleep/wake cycle
- lies in hypothalamus
-provides information from the eye about light
-Above the optic chiasm

Question 2

Describe Patricia DeCoursey et al. (2000) research into animal studies and SCN.

Answer 2

-Destroyed the SCN connections in 30 chipmunks
-Chipmunks returned to natual habitat and observed for 80 days
-Sleep/wake cycle of chipmunks disappeared and majority were killed presumably because they were awake when they should have been asleep

Question 3

What is the pineal gland?

Answer 3

-a small endocrine gland in the brain; secretes melatonin which induces sleep
-Endogenous system involved with sleep/wake cycle

Question 4

What are the limitations of research of endogenous pacemakers into sleep/wake cycle

Answer 4

-Other body clocks involved: There are many circadian rhythms in different organs and cells in the body (peripheral oscillators) e.g. lungs,pancreas and skin. They are influenced by SCN but act independently. Francesca Damiola et al. (2000) demonstrated how changing feeding patterns of mice can alter circadian rhythms of cells in the liver up to 12 hrs whilst leaving the rhythm of SCN unaffected. This sugggest complex influences on SCN

Interactionist system(endogenous pacemakers cannot be studied in isolation): Michel siffres research is very rare and he even used a lamp, artificial light which may have reset his body clock. In real life, endogenous pacemakers and exogenous zeitgebers interact and it makes little sense to split them.

-Ethical issues: In Particia Decoursey’s research (2000) chipmunks were placed in harms way when returning to natural habitat and many were killed by predators.
However, animal studies were justified as the systems are similar across the species.

Question 5

What are 2 exogenous zeitgebers that affect sleep/wake cycle?

Answer 5

-Light
-Social cues

Question 6

Describe Scott Campbell and Patricia Murphy’s research (1998) into light as an exogenous zeitgeber

Answer 6

-Demonstrated that light may be detected in skin receptor sites on the body even when the same information is not received by the eyes
-15 participants were woken up at random times in the day and a light pad shown on the back of their knees
-This caused a deviation in participants usual sleep/wake cycle of up to 3 hours
-This shows light is strong exogenous zeitgeber and does not rely on eyes to exert its influence on the brain

Question 7

Explain how social cues can affect sleep/wake cycles.

Answer 7

-Babies initial sleep/wake cycle is random but by 6 weeks the circadian rhythms begin and by 16 weeks the baby is completely entrained by the schedules imposed by parents, including meal times and bedtimes
- research onto jet lag shows that entraining to normal meal times and sleep and not responding to personal desires can help circadian rhythms establish and beat jet lag

Question 8

Evaluate exogenous zeitgebers on sleep/wake cycles?

Answer 8

-L: Environmental observations: People in Greenland live in total darkness for 6 months and yet have similar sleep patterns all year round. Therefore endogenous pacemakers mostly control sleep/wake cycle and overides changes in light

L: Case study: Laughton miles (1977) recounts study of young man who was blind since birth and yet had an abnormal circadian rhythm of 24.9 hours and could not be adjusted despite exposure to social cues such as regular meal times. This suggests that social cues are not effective in readjusting the biological rhythm.