endogenous packemakers & 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 suprachiasmatic nucleus (SCN) on the sleep/wake cycle.

Question 2

what are exogenous zeitgebers?

Answer 2

External factors that affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle.

Question 3

what is the sleep/wake cycle?

Answer 3

A daily cycle of biological activity based on a 24-hour period (circadian rhythm) that is influenced by regular variations in the environment, such as the alternation of night and day.

Question 4

what is the superachiasmatic nucleus?

Answer 4

It is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms such as the sleep/wake cycle.

Question 5

what does the SCN do?

Answer 5

It receives information about light directly from this structure. This continues even when our eyes are closed, enabling the biological clock to adjust to changing pattems of daylight whilst we are asleep.

Question 6

what was DeCoursey et al 2000’s study?

Answer 6

destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days.
The sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators (presumably because they were awake, active and vulnerable to attack when they should have been asleep).

Question 7

what was Ralph et al 1990’s study?

Answer 7

they bred ‘mutant hamsters with a 20-hour sleep/wake cycle.
When SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours.

Question 8

what is the link between the SCN and the pineal gland?

Answer 8

The SCN passes the information on day length and light that it receives to the pineal gland. This is another endogenous mechanism guiding the sleep/wake cycle.

Question 9

what happens with the pineal gland during the night?

Answer 9

the pineal gland increases production of melatonin - a chemical that induces sleep and is inhibited during periods of wakefulness. Melatonin has also been suggested as a causal factor in seasonal affective disorder.

Question 10

what is the beyond the master clock limitation?

Answer 10

-it may obscure other body clocks.
-Research has revealed that there are numerous circadian rhythms in many organs and cells in the body. These peripheral oscillators are found in the organs including the lungs, pancreas and skin. They are influenced by the actions of the SC, but also act independently. Francesca
-Damiola et al. (2000) demonstrated how changing feeding patterns in mice could alter the circadian thythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SC unaffected.
-This suggests other complex influences on the sleep/wake cycle.

Question 11

what is the interactionism system limitation?

Answer 11

-endogenous pacemakers cannot be studied in isolation.
-Total isolation studies, such as Siffre’s cave study are extremely rare.
Siffre made use of artificial light which could have reset his biological clock every time he turned his lamp on.
-In everyday life, pacemakers and zeitgebers interact, and it may make little sense to separate the two for the purpose of research.
-This suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research.

Question 12

what is the ethics limitation?

Answer 12

-Animal studies of the sleep/wake cycle are justified because there are very similar mechanisms at work across species.
0The existence of an SC and pineal gland in the brains of, say, chipmunks and hamsters means that generalisations can be made to the human brain, as the mammalian brain has similar structures.
-However, a more disturbing issue is the ethics involved in such research.
-The animals in the DeCoursey et al. study were exposed to risk when returned to their natural habitat, and most died as a result.

Question 13

what happens if there is a lack of external cues?

Answer 13

the free-running biological clock that controls the sleep/wake cycle continues to ‘tick in a distinct cyclical pattern.
This free -running cycle is then ‘brought into line’ (i.e. entrained) by environmental cues, so there is an interaction of internal and external factors.

Question 14

why is light a key zeitgeber?

Answer 14

It can reset the body’s main endogenous pacemaker, the SC, and thus plays a role in the maintenance of the sleep/wake cycle. Light also has an indirect influence on key processes in the body that control such functions as hormone secretion and blood circulation.

Question 15

what was Campbell & Murphy 1998’s study?

Answer 15

they demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by the eyes.
Fifteen participants were woken at various times and a light pad was shone on the back of their knees. The researchers managed to produce a deviation in the participants usual sleep/wake cycle of up to three hours in some cases.

Question 16

what is a babies sleep cycle?

Answer 16

newborn babies’ initial sleep/wake cycle is pretty much random.
At about 6 weeks of age, the circadian rhythms begin and, by about 16 weeks, babies’ rhythms have been entrained by the schedules imposed by parents, including adult-determined mealtimes and bedtimes.

Question 17

what does research on jet lag suggest?

Answer 17

that adapting to local times for eating and sleeping (rather than responding to one’s own feelings of hunger and fatigue) is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances.

Question 18

what is the environmental observations limitation?

Answer 18

-exogenous zeitgebers do not have the same effect in all environments.
-The experience of people who live in places where there is very little darkness in summer and very little light in winter tell a different story from the usual narrative. -For instance, people who live within the Arctic Circle have similar sleep patterns all-year round, despite spending around six months in almost total darkness.
-This suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light.

Question 19

what is the case study evidence limitation?

Answer 19

-evidence challenges the role of exogneous zeitgebers.
-Laughton Miles et al. (1977) recount the study of a young man, blind from birth, who had an abnormal circadian rhythm of 24.9 hours.
-Despite exposure to social cues, such as regular mealtimes, his sleep/wake cycle could not be adjusted.
-This suggests that social cues alone are not effective in resetting the biological rhythm.

Question 20

what is the age-related insomnia strength & limitation?

Answer 20

-Evidence suggests that people have poorer quality sleep as they get older.
-This may be due to natural changes in the circadian rhythm as we age, which means falling asleep earlier and broken sleep at night (Duffy et al. 2015).
-However, studies have suggested that exogenous factors may be more responsible for the changes in sleep patterns amongst older people. -Bernadette Hood et al. (2004) found that management of insomnia was improved if elderly people were generally more active and had more exposure to natural light.