Slides in this set
A circadian rhythm lasts 24 hours. Examples
The sleep/wake cycle: run by an endogenous
`body clock', can't be overridden by external cues.
Siffre's cave experiment, Folkard's changing clock
Core body temperature: lowest around 4.30 am
(36°C), highest around 6pm (38°C), with a dip just
after lunchtime- explains siestas. Bi-daily rhythm
linked to cognitive ability: a higher body
temperature means better cognitive reasoning.
Hormones: cortisol (stress/alertness hormone) is
at its lowest around midnight, peaking at 6am.
Melatonin (sleepy hormone) and HGH both peak…read more
Ultradian rhythms are UNDER 24 hours.
Sleep stages: Each sleep cycle takes 90 minutes.
There are five stages: 1 and 2 are light sleep
(alpha and theta waves), 3 and 4 are very deep
sleep (delta waves)and 5 is REM sleep (fast,
desynchronised EEG activity).
Basic rest-activity cycle (RAC): Also 90 minutes
long. Friedman and Fisher found clear 90 minute
cycles of eating and drinking behaviour in
psychiatric patients.…read more
Infradian rhythms are OVER 24
hours. Examples include...
Monthly cycles: the menstrual cycle, and the
alertness cycle every 20 days in males (Empson).
The menstrual cycle: Hormonal (FSH, LH and
oestrogen), but also affected by the pheromones
of other women (Russell, 1980).
Seasonal Affective Disorder: depression during
winter months and recovery during the summer.
Melatonin (released during dark hours) may cause
The SupraChiasmatic Nucleus (SCN): located
in the hypothalamus, monitors light levels
through the optic nerve. There is actually a
dorsal and ventral SCN- the ventral is more
influenced by external cues (light), whereas
the dorsal is less easily thrown.
DeCoursey found that SCN-lesioned
chipmunks were more likely to be eaten by
weasels in the wild, supporting the theory that
the sleep is adaptive.
The pineal gland: directed by the SCN to
produce melatonin at night.…read more
Light: can reset the SCN. The protein-clock,
CRY, is light-sensitive. Campbell and Murphy
found that a light shone on the back of the
knees can shift circadian rhythms.
Social Cues: influence sleep/wake times. The
zeitgeber for cells in the heart and liver is set
by mealtimes (Davidson).
Temperature: a factor in the onset of
Disrupting Biological Rhythms: Shift
Knutsson: working shifts for over 15 years triples the risk of heart
More accidents occur during the 1-4am shift than any other time:
Chernobyl, Three Mile Island.
The optimal shift pattern is a rotating system: changing forward
through night/morning/evening shifts every 21 days. This prevents
the accumulation of sleep deprivation (Monk and Folkard).
Gordon: this optimal pattern reduces accidents by 40% in police
Can be treated with phototherapy: strong artificial light can reset
body temperature and cortisol cycle within 3 days.
Applicability- healthcare, transport etc. run 24/7. Research can
decrease health risks of rhythm disruption and prevent accidents
during night shifts.…read more