Lesson 9 Flashcards
What is an endogenous pacemaker
mechanisms within the body e.g. internal body clocks that regulate our biological rhythms such as the influence of the suprchiasmatic nucleus (SCN) on the sleep / wake cycle.
What is an exogenous zeitgeber?
an external environmental cue, e.g. light and social cues that helps regulate our biological rhythms.
There are two endogenous pacemakers within the body.
- suprachiasmatic nucleus (SCN).
- pineal gland
The suprachiasmatic nucleus (SCN)
- SCN is tiny cluster of nerve cells which are located in the hypothalamus of both hemispheres.
- primary endogenous pacemaker in mammalian species (including humans).
- influential in maintaining the circadian rhythms such as the sleep / wake cycle.
- The SCN acts as the master clock, controlling other biological rhythms.
- nerve fibres are connected to the eye cross in an area called the optic chiasm on their way to the visual area of the cerebral cortex.
- This continues even when our eyes are closed, which allows our biological rhythm to adjust even when we are asleep.
Supporting evidence for the SCN
aim - influence of the SCN has an chipmunks.
procedure - destroyed the SCN in 30 chipmunks and retuned them to the natural habitat (burrows) for an observation for 80 days.
- most of them had been killed as their sleep/wake cycles was destroyed (awake and restless) so their predators were able to find them.
no SCN no biological rhythms.
ralph et al
aim - influence the SCN has on hamsters.
procedure - took the SCN out of genetically abnormal with the usual 24hr cycle.
findings - normal hamster cycles shortened to 20hrs.
conclusion - SCN is key in establishing a sleep / wake cycle.
Pineal gland and the role of melatonin
- the SCN sends signals to the pineal gland , directing it to increase production and secretion of melatonin at night and then decrease it as light levels increase in the morning.
as inc in melatonin induces sleep.
melatonin is suggested to be the casual factor of seasonal affective disorder.
The SCN signals the pineal gland to produce a hormone at night, to induce sleep.
Exogenous zeitgebers
An external environment cue light and social cues that helps regulate our biological rhythms through the process of entrainment.
without external cues our free - running biological clock continues to tick.
the sleep/wake cycle is brought in line i.e. entrained by environmental cues.
light -
- receptors in the SCN are sensitive to changes in light levels during the day and use this information to help synchronize activity.
- light can reset the body’s endogenous pacemaker, the SCN which maintains the sleep/wake cycle.
campbell and murphy
aim - investigated how powerful light in an exogenous zeitgeber and whether it can be detected any other way besides the eyes.
procedures - 15 ppts were woken at various times with light being shone at the back of their knees.
findings - they found there were changes in the sleep/wake cycle, some ppts changes up to 3 hrs.
therefore, this suggests that light is a powerful exogenous zeitgeber and we do not need it to enter our eyes to influence our brain and the SCN.
Social cues
- social stimuli - mealtimes and social activities can act as zeitgebers.
Aschoff et al showed that individuals can compensate for the absence of zeitgebers like natural light by responding to social zeitgebers.
found circadian rhythms of air travelers can be adjusted more quickly if they outside more at their destination. This is because they were exposed to the social cues of their new time zone which acted as a zeitgeber.
What are social cues?
in infants the sleep/wake cycle is initially random but by 6 weeks the circadian rhythms begin and by 16 weeks most babies are entrained.
schedules and social cues determined by the parents - mealtimes and bedtimes.
this also helps with jet lag - rather than responding to hunger and fatigue, conforming to local times for sleeping and eating will train your circadian rhythm.
the role of peripheral osscilators
limitation of the SCN is it may be too simplistic to suggest that the suprachiasmatic nucleus is the only endogenous pacemaker.
research has revealed that there are numerous circadian rhythms in many organs and cells in the body. these peripheral oscillators are found in organs including the lungs, pancreas, and skin. They are influenced by the actions of the SCN but also have the ability to work independently.
demonstrated that changing feeding patterns of mice could alter the circadian rhythms of cells in the liver upto 12 hrs, whilst leaving the rhythm of the SCN unaffected.
This suggests that there are other influences on circadian rhythms, aside from the SCN.
interactionist system
limitation is that endogenous pacemakers cannot be studied in isolation.
for example, total isolation studies, such as Siffre’s cave study are extremely rare.
in the context of the sleep/wake cycle, where both endogenous pacemakers and exogenous zeitgebers (light) are used to help maintain this circadian rhythm and must work together in order to facilitate this.
Therefore, it would be better to adapt a more interactionist approach when investigating the role of endogenous pacemakers and exogenous zeitgebers to understand how they work together.
practical application - jet lag
strength of our understanding of exogenous zeitgebers is the practical application to help avoid jet lag (severe condition disturbing sleep appetite and mood.
exposure to bright light prior to an east west flight decreased the time needed to readjust to local time on arrival.
individuals who must take long haul flights for business can improve their productivity and concentration upon landing at their destinations and get on with their jobs more rapidly.
Therefore, by understanding the role of exogenous zeitgebers have on our sleep, we can entrain our circadian rhythms to fit into changing time zones to reduce the impact of jet lag.
