This 3 page document includes a summary of Circadian Rhythms for Biopsychology Y2.
Disclaimer: there may be some information missing due to COVID-19 reduced content in 2022 A levels.
But this includes information on biological rhythms, the sleep-wake cycle, light, homeostatic control, body ...
Circadian Rhythms
Biological rhythms
Biological rhythms are cyclical changes in the way that biological systems
behave.
These rhythms evolve because the environment within which we live has cyclic
changes -e.g., menstrual cycle, hibernation.
Nearly all organisms possess a biological representation of the 24 hour day –
these circadian rhythms (body clock) optimize the organism’s physiology and
behaviour to meet the demands of the day/night cycle.
Circadian rhythm – a pattern of behaviour that occurs or recurs approximately every
24 hours, and which is set and reset by environmental light levels.
KEY EXAMPLE: Sleep-wake Cycle – the alternating states of sleep and waking that
are dependent on the 24-hour circadian cycle.
Human response to Circadian rhythms
Circadian rhythms are driven by our body clocks, found in all the cells of the
body, and synchronized by a master circadian pacemaker known as the
suprachiasmatic nucleus, found in the hypothalamus.
This pacemaker must be reset so our bodies are in sync with the outside world.
Light
Provides the primary input to this system, setting the body clock to the correct
time – this is known as photoentrainment.
Mammals have light-sensitive cells within the eye which act as brightness
detectors.
They send messages about environmental light levels to the suprachiasmatic
nucleus (SCN), which then uses this information to coordinate the activity of
the circadian system.
A key example of this entrainment process is the Sleep-Wake cycle.
Sleep-wake Cycle
Circadian rhythms dictate not only sleep, but also wakefulness, using the
external signal of light and dark.
The circadian rhythm also dips and rises at different times of the day, so usually
our strongest sleep drive occurs in two dips (2-4am and 1-3pm).
E.g., people who work night shifts make the most mistakes between 2-4am,
because our bodies drive to sleep is strongest.
The level of sleepiness we experience at these times depends on whether we
have had sufficient sleep or are sleep deprived.
Other things that may determine sleep and wakefulness are things like social
media, social factors like noise (not just light that determines it) –
reductionist
Homeostatic control
Homeostasis refers to the maintenance of regular processes.
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