Biological rhythms : Influences on the sleep/wake cycle

Question 1

Example of an exogenous pacemaker on the sleep/wake cycle

Answer 1

• suprachiasmatic nucleus (SCN) is a group of nerve cells, located in the hypothalamus in each hemisphere of the brain
• hypothalamus- primary endogenous pacemaker that mainatains the circadian rhythm
• SCN receives info about light from the optic chiasm (nerve fibres connected to eye) - continues even when eyes are closed, enabling the biological clock to adjust to changing patterns of daylight even when were are asleep
• SCN passes the info on daylight to the pineal gland which increases the production og maelatonin when there are low daylight levels
• melatonin reduces brain activity which induces sleep

Question 2

Examples of exogenous zeitgebers affecting the sleep/wake cycle

Answer 2

1. (artificial) light - key zeitgeber in humans. light has an impact on melatonin production and therefore, sleep/wakefulness
2. social cues- idea that our biological rhythms are entrained through social convention. we are influenced by the norms of people around us as to what time we wake and sleep e.g. school

Question 3

Research into the impact of endogenous pacemakers and exogenous zeitgebers

Answer 3

1. Campbell and Murphy
2. Baby research
3. Miles et al
4. Arctic research

Question 4

Campbell and Murphy

Answer 4

1988
* 15 ppts woken up at various times during the night and a light pad was shone on the back of their knees
* researchers managed to vary their sleep cycle by up to 3 hours
conclusion: study shows that light is an important exogenous zeitgeber; its not only the eyes that act as a light receptor but also the skin

Question 5

Baby research

Answer 5

• when babies are first born, their sleep patterns are erratic
• by 6 weeks their circadian rhythms start and by about 16 weeks they tend to be in a routine
  conclusion: shows that social cues are an important exogenous zeitgeber because of the schedule imposed by parents. parents entrain the sleep/wake cycle by setting times for eating and sleeping

Question 6

Miles et al

Answer 6

1977
* reported 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 could not be adjusted and consequently he had to take sedatives at night and stimulants in the morning to keep pace with the 24 hour world
conclusion: shows that social cues were not affecting his sleep/wake patterns

Question 7

Arctic research

Answer 7

• similarly, studies of people who live in arctic regions (where the sun doesnt set in summer) show normal sleep patterns
  conclusion: this shows there are occasions where exogenous zeitgebers such as light have little effect on our internal rhythms

Question 8

conclusion

Answer 8

• it can be said that in real life, endogenous pacemakers and exogenous zeitgebers interact and thus it is wrong to seperate them
• both are important influences on the circadian rhythm