PSYA3 Biological Rhythms

Full notes on the biological rhythms topic

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Biological Rhythms
Biological Rhythms- regular patterns of physiological, cognitive and behavioural activity occurring
as circadian, ultradian and infradian rhythms
Circadian Rhythms- bodily cycles occurring every 24 hours
Infradian Rhythms- bodily cycles occurring less than once a day
Ultradian Rhythms- bodily cycles occurring more than once a day
Endogenous Pacemakers- internal body clocks regulating biological rhythms
Exogenous Zeitgebers- external stimuli involved in the control of biological rhythms
Shift Work- periods of work performed outside regular employment hours
Jet lag- temporary disruptions of biological rhythms caused by high-speed travel across time zones
Circadian Rhythms
-Circadian rhythms are biological cycles lasting around 24 hours, like the sleep/wake cycle, which is
usually facilitated by time-checks and regular events like mealtimes. There is a free running cycle
controlled by an endogenous pacemaker working as a body clock. Another circadian rhythm is body
temperature, rising and declining as an indicator of metabolic rate, 4 am being the lowest point.
-Mammals possess about 100 circadian rhythms. The 24-hour sleep­waking cycle is a good example
of a circadian rhythm because it clearly illustrates that circadian rhythms depend on an interaction of
physiological and psychological processes. Our fairly consistent sleep pattern suggests an internal or
endogenous mechanism--the biological clock. But this can be overridden by psychological factors
such as anxiety.
Endogenous Pacemakers
- An endogenous clock is proposed as some sort of innate mechanism that sets the timing of
biological rhythms
-The SCN (suprachiasmatic nucleus) is a bundle of nerves in the hypothalamus. It is connected to the
retina in the eye, so when the retina is exposed to light, signals are sent to the SCN. The SCN is also
connected to the pineal gland. The pineal gland converts serotonin (neurotransmitter) into melatonin
(hormone that plays a role in inducing sleep). The SCN controls the release of melatonin from the
pineal gland, so when the retina is receiving low levels of light, the SCN signals the pineal gland to
increase the release of melatonin, and when light levels rise, the pineal gland releases less
melatonin. Therefore it plays a large role in regulating the circadian rhythm. For example, if the sun
rises earlier than the day before, morning light will shift the endogenous pacemaker to regulate the
body's circadian rhythm in synch with its environment. Alternatively, the SCN sends a message at
night when there is no light to the pineal gland, causing it to increase the production of melatonin,
which induces sleep by preventing the brain's mechanism to promote wakefulness

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Exogenous Zeitgebers
Light is a dominant zeitgeber in humans. Light can reset SCN and other oscillators in the body as
protein cryptochrome (CRY) is light sensitive. Campbell and Murphy (1998) shined light on back of
pp's knees and shifted circadian rhythms supporting the role of exogenous zeitgebers.…read more

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It seems unlikely that humans have evolved with a faulty biological clock running every 25
hours. Animal studies show a 24-hour cycle and it makes more sense for humans to follow
this pattern
Isolating participants from the environment without controlling their behaviour may be
insufficient to reveal the activity of the endogenous circadian pacemaker.…read more

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Research into SAD led to effective therapies, such as phototherapy. This uses very strong
lights in the evening and/or early morning to change levels of melatonin and serotonin. SAD
sufferers have reported that daily use is enough to relieve them of their symptoms. There
are questions about whether this may be due to a placebo effect.…read more

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Some studies have found that 70% of participants report dreams during NREM sleep.…read more

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Cooligan et al (1978) found that workers with shift rotations had more accidents than workers on
set shifts.…read more

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Sleep does not provide
any repair function in humans, except for the brain
-Shapiro et al (1981) found that long-distance athletes, slept for longer, suggesting that sleep aids
restoration.…read more

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Bently (2008) points out that snoring is a difficult phenomenon to explain, as it is likely to
increase vulnerability to predation by attracting attention while sleeping
Problems with generalising animal studies to humans
Methodological issues: observational studies- little control over extraneous variable but high
ecological validity
Empson (1989) described Meddis' theory as a `waste if time'. Sleep is universal among
animals and on occasions going without sleep can be fatal.…read more

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REM sleep for premature babies
-Puberty marks the onset of adolescence and sexual and pituitary growth hormones are released in
pulses during SWS
-Males experience wet dreams and both sexes may experience erotic dreams
-Circadian rhythm also changes so that teenagers feel naturally more awake later at night and have
more difficulty getting up (phase delay)
Evaluation- Teenagers
Hormonal changes can explain the upset t circadian clock- `delayed sleep phase syndrome'.
The changes of sleep patterns in adolescence may be linked to hormone production.…read more

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Practical Applications- schools opening later due to teenagers being biologically
programmed to wake up later
Sleep labs include objective measures and thus is falsifiable supporting the is psychology a
science debate.…read more


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