the effect of endogenous pacemakers and exogenous zeitgebers on the sleep/wake cycle Flashcards
biopsychology
What are endogenous pacemakers?
Endogenous means having an internal cause and pacemakers refers to anything that sets a steady pace. They are our internal biological rhythms, and there are 2 endogenous pacemakers linked to the sleep/wake cycle.
What is the suprachiasmatic nucleus (SCN)?
An area of the hypothalamus in each hemisphere which acts as a clock. It’s the main endogenous pacemaker that controls other biological rhythms. Once light signals enter the optic chiasm they then travel to the SCN which communicates with the pineal gland to regulate the sleep/wake cycle.
What does the pineal gland do in response to light?
The SNC communicates with the pineal gland in response to light.
Darkness = increased melatonin causing feelings of sleepiness
Daylight= reduced melatonin causing us to feel awake and alert.
What are exogenous zeitgebers?
Exogenous means having an external cause and zeitgeber comes from the German ‘zeit’ which means time and ‘geber’ which means giver. They are external factors that also regulate biological rhythms and there are two thought to affect the sleep/wake cycle. Light and social cues.
Light as an exogenous zeitgeber.
It’s an important source of information which tells us whether we should be a sleep or awake. The SCN is sensitive to light so it may be that these 2 factors interact to control our sleep/wake cycle.
Social cues as an exogenous zeitgeber.
Other sources of information that might affect our sleep/wake cycle. These can include clocks, and meal times. New born babies have feeding schedules to help set these cycles for them.
What are the strengths of endogenous pacemakers?
It has research to support it, Morgan (1955)they bred hamsters to have abnormal circadian rhythms- some of the nerve cells from the SCN of these abnormal hamsters were transplanted into the brains of normal hamsters causing them to display an abnormal circadian rhythm of 20 hours. This supports the significance of the SCN.
What are the limitations of endogenous pacemakers?
It’s very difficult to study the influence of these alone. Very few studies, e.g. Michel Siffre who spent 179 days in a cave, still had some artificial light. This could have influenced his endogenous pacemakers, so it’s difficult to know which of these two has the greatest influence.
What are the strengths of exogenous zeitgebers?
There is research to support- Klein and Wegmann (1974)- interested in jet lag and found that adjustments to a new time zone happened faster when people spent more time outside- in so they were being affected by exogenous zeitgebers-adjustments took longer in the absence of external cues-supports the theory that exogenous zeitgebers are important in regulating biological rhythms.
What are th limitations of exogenous zeitgebers?
They don’t have the same influence on our biological rhythms in all environments- northern hemisphere has 24 hour daylight in summer and very little daylight in the winter but people who live there don’t see a change in their sleep/wake cycle. This limits the role of exogenous zeitgebers and suggests our internal biological clocks have more of an influence.
