Endogenous pacemakers and exogenous zeitgebers Flashcards
What are endogenous pacemakers?
Internal bodily clocks that may regulate rhythms.
Where is the Suprachiasmatic nucleus located?
The hypothalamus.
What is the role of the suprachiasmatic nucleus?
The SCN receives information about light and passes this information to the pineal gland. The pineal gland produces melatonin (the amount will change according to the light information). At night, the pineal gland produces more melatonin- a hormone which induces sleep. If there is more light, production of melatonin is delayed.
Give an example of an endogenous pacemaker?
The suprachiasmatic nucleus.
What is the hormone melatonin responsible for?
Inducing sleep.
What happens if there is a lot of light at night?
Production of melatonin is delayed.
Give research support involving animals for the SCN as an endogenous pacemaker.
Decoursey et al 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 even killed (they were awake and vulnerable to attack when they should have been asleep).
What is an exogenous zeitgeber?
External factors in the environment which restart our bodily clocks.
Give examples of exogenous zeitgebers.
Light
Social cues
Why is light an exogenous zeitgeber?
Light is a key zeitgeber in humans as it can reset the body’s endogenous pacemaker. Light plays a role in the maintenance of our sleep/wake cycle.
Study into light as an exogenous zeitgeber.
Campbell and Murphy demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by our eyes. 15 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.
Why are social cues exogenous zeitgebers?
At about 6 weeks of age, circadian rhythms begin in babies and by about 16 weeks a baby rhythms have been entertained by the schedules imposed by parents, including adult-determined meal times and bed times.
Give a limitation of research into endogenous pacemakers and exogenous zeitgebers (SCN may obscure other body clocks).
Research has revealed that there are numerous circadian rhythms in many organs and cells in the body. These suggested oscillators are found in the organs including the lungs, pancreas and skin. They are influenced by the actions of the SCN, but also act independently. For example, Damiola demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours whilst leaving the SCN unaffected. This suggest other complex influences on the sleep/wake cycle.
Give a limitation of research into endogenous pacemakers and exogenous zeitgebers (endogenous pacemakers cannot be studied in isolation).
Total isolation studies, such as Siffre’s case study, are extremely rare. In everyday life, pacemakers and zeitgebers could have reset his biological clock every time he turned the lamp on. In everyday life, pacemakers and zeitgebers interact and it makes little sense to separate the two for the purpose of research.
