Biopsychology: Circadian Rhythms Flashcards
What are Biological rhythms?
> Distinct patterns of change in the body that conform to cyclical time periods. A circadian rhythm is a biological rhythm with two defining features: they have a free running cycle of 24 hours and they can be entrained.
Two types of biological rhythm : ultradian=less than 24 hours, infradian= more than 24 hours.
Circadian rhythms are free running, meaning they happen in the absence of external cues.
The free running nature of circadian rhythms is maintained by endogenous pacemakers which are bodily processes, often chemical, that take about 24 hours to complete a cycle.
Another feature is that they can be entrained through a process of entrainment. Meaning they can be reset by exposure to external stimuli.
Entrainment of circadian rhythms is coordinated by the body’s master endogenous pacemaker, the suprachiasmatic nucleus (SCN). It constantly resets its own 24 hour cycle in response to light levels. It communicates with the endogenous pacemakers, synchronising the body’s various circadian rhythms.
An example of circadian rhythms are the sleep and wake cycles. Or the core body temperature.
What are disruptions to the body’s circadian rhythms?
Jet lag is an illustration of how circadian rhythms can be disrupted. A free running cycle will remain tied to the day night cycle of the time zone they have left. e. Over time, the SCN, via entrainment, will prompt the various
endogenous pacemakers to adjust their rhythm. The new environments light cues will match a new 24 hour cycle. The adjustment to the new cycle will take time.
Explain what determines the sleep and wake cycle.
> The endogenous pacemakers and exogenous zeitgebers.
It is under control by sleep pressure. Light and darkness areas exogenous zeitgebers, meaning we tend to feel sleepy when it’s dark and awake when it’s light. Sleep pressure is another factor. When a person is awake for a long time, sleep pressure increases the need for sleep due to the need to restore the body’s energy that has been depleted during wakefulness.
What research is there into the ways in which sleep/wake cycle is a circadian rhythm?
Siffre (1962) spent two months deep underground in the caves of the Southern Alps, with nothing apart from a small lamp. During this time, he found his sleep/wake cycle increased slightly, to around 25 hours.
Siffre’s research demonstrates that the sleep/wake cycle is a circadian rhythm
as it is free-running. Although Siffre’s sleep/wake cycle did change a bit, it still maintained a rhythm close to 24 hours. This suggests it is free running, meaning it
can maintain a roughly 24-hour rhythm without the presence of external cues (like daylight). Furthermore, the fact that his sleep/wake cycle did extend to 25
hours suggests that natural state of the free-running sleep/wake cycle is longer
than 24 hours. This suggests that the reason humans generally have a 24-hour sleep/wake cycle is because their sleep/wake cycles are entrained by exposure to the light cues (exogenous zeitgebners) of the 24-hour day/night cycle, which Siffre
missed while underground. underground. However, these conclusions may be in doubt as Siffre
brought a lamp with him underground. By turning this on when he woke and off
when he went to sleep, he introduced an exogenous zeitgeber into his study that
could have helped entrain his sleep/wake cycle. Perhaps without this his sleep/wake cycle would have been different. Bringing this lamp introduced a
confounding variable that undermined the internal validity of Siffre’s research.
Another issue to be aware of is that this study was only on a single person, and
this may mean generalising to everyone’s circadian rhythms may be difficult.
Why is research into circadian rhythms important implications for health?
Research into the effect of shift-work (where workers are required to work some night shifts) on health has found that shift workers are three times more likely to develop heart disease than workers who do not have to do shift work. This shows how the disruption of our natural circadian rhythms – which occurs
when a worker has to stay awake at night, when their free-running rhythm would
encourage them to sleep – can be damaging to health. This has economic
implications, as the health costs of shift-work will result in people becoming
unwell, requiring expensive medical attention and/or being unable to work,
rendering them economically inactive.
What has research found about the differences in timings of circadian rhythms?
For example, Duffy et al. (2001) found that ‘morning people’ prefer to rise and go to bed early (about 6 am and 10 pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am). Understanding how the timing of circadian rhythms vary for individuals could
benefit society by, for example, allowing organisations to tailor work schedules to
suit an employee’s individual circadian rhythm, thereby maximizing that person’s productivity. This means that research into the individual differences of circadian rhythms has economic implications, as it could help workers be more productive.
