Endogenous pacemakers and Exogenous Zeitgebers Flashcards
What is an endogenous pacemaker?
Internal body clocks that regulate many of our biological rhythms, such as the influence of the suprachiasmatic nucleus.
Explain animal studies investigating the suprachiasmatic nucleus.
DeCoursey et.al destroyed the SCN connections in the brains of 30 chipmunks who were returned to their natural habitat and observed for 80 days.
It was found that the sleep wake cycle had disappeared and many had been killed by predators.
Ralph et.al bred mutant hamsters with a 20-hour sleep/wake cycle. When the CNS 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.
How does the endogenous pacemaker control the sleep- wake cycle?
The SCN passes the information on day length and light that it receives to the penal gland. During the night, the penal gland increases the production of melatonin- a chemical that induces sleep and is inhibited during periods of wakefulness.
Limitation of the SCN research- Other complex influences on the sleep/wake cycle.
There may be numerous circadian rhythms in many organisms and cells in the body.
Damiola- demonstrated how changing feeding patterns in mice could alter their circadian rhythms of cells in the liver by up to 12 hours, and leaving the SCN unaffected.
Limitation to endogenous pacemakers research on animals.
Ethical issues- damaging the chance of survival for an animal and potentially making it suffer.
What is an exogenous zeitgeber?
External factors that affect of entrain our biological rhythms, such as the influence of light on our sleep/ wake cycle.
Explain light as an external cue for exogenous pacemakers.
It can reset the body’s main endogenous pacemaker, the SCN and plays a large role in the sleep/ wake cycle.
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 the eyes. They gathered 15 participants and woke them up at various times of the night and shone a light on the back of their knees.
They researchers were able to deviate the participants sleep/wake cycle up to 3 hours.
Explain social cues as an external cue for exogenous pacemakers.
Research on jet lag suggests that adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances.
Limitation of exogenous pacemakers.
They do not have the same effect in all environment. People who live in the Arctic circle and live in complete darkness 6 months of the year have similar sleep patterns all year round.
Limitation of exogenous pacemakers- case study evidence.
Miles 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.
This suggests that social cues alone are not effective in resetting the biological rhythm.
