EFFECT OF ENDOGENOUS PACEMAKERS AND EXOGENOUS ZEITGEBERS ON SLEEP/WAKE CYCLE

Question 1

outline exogenous

Answer 1

• exogenous zeitgebers are external cues that may affect our biological rhythms, such as the influence of light on the sleep/wake cycle.
• Exogenous zeitgebers influence biological rhythms: these can be described as environmental events that are responsible for resetting the biological clock of an organism.
• They can include social cues such as mealtimes and social activities, but the most important zeitgeber is light, which is responsible for resetting the body clock each day, keeping it on a 24-hour cycle

Question 2

outline endogenous pacemakers

Answer 2

• Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms, such as the influence of the SCN on the sleep/wake cycle.
• The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
• The SCN lies just above the optic chiasma which allows it to receive light information directly from the optic chiasma.
• This light information is received by the SCN even when our eyes are closed, allowing the biological clock to adjust to changing patterns of daylight.
• The SCN passes the information to the pineal glands. At night the pinealgland increases the production of melatonin (which induces sleep).
• Melatonin production is inhibitedduring periods of wakefulness.

Question 3

Ethics

Answer 3

• animal studies on the sleep/wake cycle are justified because there are similar mechanism in all mammals.
• so generalised can be made to the human brain.
• however a disturbing issue is the ethics invoved. animals were exposed to huge risks in decoursey et al study and most died as a result.
• this suggests that studies like these cannot be justified and researches should find alterantive ways of studying endogenous pacemakers.

Question 4

Endogenous pacemakers cannot be studied in isolation

Answer 4

• only in exception circumstances are endogenous pacemakers ‘free running’ and unaffected ny the influence of exogenous zeibegters.
• total isolation studies are rare. in everyday life, pacemakers and zeibeters interact it may make little sense to seperate the two
• this suggests the more the researchers attempt to isolate the influence of internal pacemakers the lower the validity

Question 5

One strength of EP is that there is supporting research.

Answer 5

• For example, Siffre spent 7 months in a cave, where despite being fed and physically active, he lacked any cues about when it was day/night such as clocks and lights.
• It was found that despite this, his sleeping pattern settled to just over 24 hours.
• This shows patterns of sleep and waking are internally controlled by endogenous pacemakers as they are
  often not influenced by changes in our external environment.
• This supports the role of biological and endogenous factors on our sleep cycles, which increases the validity of the theory

Question 6

One strength of EZ is that there are useful real life applications.

Answer 6

• For example, Burgess found that when participants were exposed to continuous bright light before their long flight to a far destination, their circadian rhythms shifted by 2.1 hours over the course of their study.
• As a result, participants felt sleepier 2 hours earlier in the evening and were well adjusted to the local time at their destination upon arrival.
• This supports our understanding of exogenous zeitgebers as it shows the influence that external cues such as bright light can have over our sleep-wake patterns.
• Therefore we are able to implement our understanding into the real world, which prevents jet lag. Therefore it has useful applications to real life

Question 7

SR: EP

Answer 7

• For example, Ralph et al bred mutant hamsters with a 20 hour sleep wake cycle.
• When the SCN cells from the foetal tissues of mutant hamsters were transplanted into the brain of normal hamsters, the cycle of the normal hamsters defaulted to 20 hours.
• This suggests the SCN is the most influential factor in our sleep wake cycle; without it our sleep becomes unregulated.
• This is an advantage as we are able to further understand the role of endogenous pacemakers