Biopsychology: Exogenous Zeitgebers And Endogeneous Pacemakers Flashcards
How are Biological Rhythms maintained?
Through clocks known as endogenous pacemakers. These bodily processes often chemical that maintain a constant cyclical rhythm.
Outline the suprachiasmatic nucleus.
> The most important endogenous pacemaker in the body. This is a bundle of nerves in the brains hypothalamus, between the eye and the visual cortex.
The SCNs means it receives information about the intensity of environmental light from the eyes. It reacts to this information by adjusting its own biological rhythm and the instructing other pacemakers to do the same.
It is able to adjust the sleep/wake cycle indirectly by sending information about light levels to another pacemaker (a peripheral clock) called the pineal gland, located just behind the hypothalamus.
What is the purpose of the pineal gland?
> Located behind the hypothalamus
when light levels are low, the pineal gland secretes melatonin, a hormone that induces sleep. And when light levels are high, the secretion of melatonin is inhibited, promoting wakefulness.
The primary zeitgeber for the the sleep/wake cycle is light. Light entrains the body’s sleep/wake cycle so that it matches the day/night cycle of the environment.
Even when closed, photoreceptor cells in the eye receive information about the intensity of
environmental light. They then send this information to the SCN.
What are social cues?
These can also act at exogenous zeitgebers. For example, only start developing clear
circadian rhythms (e.g., a regular sleep/wake cycle) by about 16 weeks of age. The feeding schedules and bedtimes imposed by parents may act as exogenous zeitgebers that entrain
their rhythms.
What research is there on the sleep/wake cycle that has real life implications?
Research into the role of exogenous zeitgebers and endogenous pacemakers on the sleep/wake cycle has real-life implications. Sleep deprivation is a growing problem in the modern world. Issues with sleep have been linked with every mental health condition, as well as a huge range of physical health conditions. Research into the role of exogenous zeitgebers and endogenous pacemakers on the sleep/wake
cycle has helped reveal how features of the modern world, such as increased use of blue-light
emitting devices, are resulting in sleep deprivation. This research can also inform guidance on better
‘sleep hygiene’, which may ultimately benefit the mental and physical health of modern humans. Such research has also led to other interventions, such as the prescribing of melatonin for people
who suffer from sleep disorders.
What is the importance of the SCN on the sleep/wake cycle?
The importance has been demonstrated in research. DeCoursey (2000) destroyed the SCN connections in the brains of 30 chipmunks, after which they
were observed for 80 days in their natural habitat. The researchers observed how their sleep/wake cycle was severely disrupted. Additionally, most of the chipmunks were killed by predators during the 80 days of observations. This finding demonstrates the importance of the SCN – the body’s master pacemaker – for
regulation of the sleep/wake cycle: if the SCN wasn’t crucial, then we would expect the chipmunk’s
sleep/wake cycle to remain unaffected. Moreover, the deaths of many of these chipmunks
presumably occurred because their unregulated sleep/wake cycle of these chipmunks led them to
be awake and exposed at times of the day when predators were around. This suggests the evolution
of a sleep/wake cycle regulated by the SCN was naturally selected, as it gave animals with this
regulation a survival advantage, allowing them to pass on this feature to their offspring. However,
this research is flawed because of its use of chipmunks. Humans would respond very differently to
manipulations of their biological rhythms, not only because we are different biologically, but also because of the vast differences between environmental contexts. This makes research carried out on other animals unable to explain the role of endogenous pacemakers in the biological processes of
humans.
How has research into the effects of exogenous zeitgebers and endogenous pacemakers illustrate the importance of taking an interaction approach?
Interactionist explanations challenge simple nature vs nurture accounts of phenomena, as they
explore the ways in which biological and environmental factors interact. Explaining the sleep/wake cycle with reference only to biological factors or environmental factors
is impossible, as neither factor by itself can regulate the sleep/wake cycle. Instead, explaining the
regulation of the sleep/wake cycle requires accounting for how environmental stimuli (like the exogenous zeitgeber of light) and biological components (like the SCN and pineal gland) interact in a
dynamic way.
