Endogenous Pacemakers and Exogenous Zeitgebers Flashcards
what are endogenous pacemakers
Internal Body Clocks that regulate our biological rhythms e.g. the effect of the SCN on our circadian rhythms and the sleep/wake cycle
what are Exogenous Zeitgebers
External cues that affect our biological rhythms e.g. the influence of light on the sleep/wake cycle
what is the AO1 for endogenous pacemakers and the sleep/wake cycle
- The suprachiasmatic nucleus or SCN is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
- It receives information about light (from the optic chiasm, which it lies above, hence “supra”. The optic chiasm is where nerve fibres connected to the eye cross).
- This pacemaker must be constantly reset so that our bodies are constantly in synch with the outside world.
- Light provides the primary input to this system, setting the body clock to the correct time.
- In mammals, light sensitive cells in the eye act as brightness detectors and send messages to the SCN to help regulate our circadian rhythms.
- The SCN passes the information on day length and light that it receives to the pineal gland, and the pineal gland increases or decreases the amount of melatonin (sleep hormone) it produces in response to this.
what are the AO3 points for endogenous pacemakers
- mutant chipmunks
- mutant hamsters
- alternative endogenous pacemakers to the SCN
expand on the +ve AO3 point, mutant chipmunks
- Psychologists destroyed the SCN connections in the brains of 30 chipmunks.
- They were returned to their natural habitat and observed for 80 days.
- The sleep/wake cycle disappeared and by the end of the study a significant proportion had been killed (because they were awake and vulnerable to attack when they would usually be asleep).
expand on the +ve AO3 point, mutant hamsters
- Another psychologist bred “mutant” hamsters with 20 hour sleep/wake cycles.
- When tissue from the SCN of these hamster foetuses was transplanted into “normal” hamsters they defaulted to the same 20 hour cycle.
- Both of these studies show how crucial the SCN is as an endogenous pacemaker controlling our sleep/wake cycles.
expand on the AO3 point, alternative endogenous pacemakers to the SCN
- Recent research has demonstrated that alternative endogenous pacemakers exist in other cells and organs in the body, and that these pacemakers can run independently from the SCN.
- This suggests that there may be other important endogenous pacemakers affecting our sleep-wake cycle and that more research is needed to understand how this all fits together.
what is the AO1 for Exogenous Zeitgebers
- The German word “zeitgeber” means “time-giver”.
- Exogenous zeitgebers are external factors in the environment that reset our biological clocks through a process called “entrainment”.
- You have already learned that in the absence of external cues (Siffre’s cave) the body attempts to continue in a free-running circadian rhythm.
- It seems that the sleep/wake cycle is therefore controlled by BOTH internal and external factors.
LIGHT
- Light is obviously a key ZEITGEBER in humans.
- Light has the ability to RESET the body’s ENDOGENOUS PACEMAKER (as in, over-ride it!) so it is incredibly influential.
what is AO3 light study
- Psychologists woke 15 pps at various times during the night and shone light pads onto the backs of their knees.
- The result was that their usual sleep/wake cycle was thrown out by up to three hours.
- This study shows that light need not be detected by the eyes in order to have an effect.
what is the AO1 for eating
Eating is another important EXOGENOUS ZEITGEBER that can help regulate the sleep-wake cycle.
what is the AO3 for eating
Psychologists have shown that if changing time zone, shifting immediately to the mealtimes of the new country of origin helps reset the sleep/wake cycle much more quickly.
what is the AO3 - how important are exogenous zeitgebers (compared to endogenous)
- As you have seen from Siffre’s Cave study, Wever and Folkard, when zeitgebers were removed the body wanted to continue to run on a 24 hour sleep/wake cycle.
- This suggests that ENDOGENOUS pacemakers are more vital!
