biological rhythms Flashcards
why are circadian rhythms?
-biological rhythms that last a day, eg sleep/wake cycle
-usually measured by recording the times of regular events eg eating and sleeping
-our body clock is regulated by an internal system including factors like release of hormones including melatonin, metabolic rate and body temperature
research on circadian rhythm
-siffre 1975 - spent 6m in a cave with no natural light/ clues of date/time, when he was awake he had artificial light and kept himself busy, let his internal body clock free-run, settled into a sleep-wake cycle of 25-30h, lost track of amount of days, believed he was in there one month less than he actually was, 179 days, shows importance of light sources in environment
what are endogenous pacemakers?
rhythms generated from internal bodily systems, can be affected by environment
-still function without cues from the environment, altho circadian rhythm can vary as a consequence
-suprachiasmatic nucleus (SCN) seems to be the most influential endogenous pacemaker in the body, is in the centre of the brain and is regulated by environmental light
-found in animals which is good for research (unethical on humans)
research on endogenous pacemakers
-ralph et al 1990 - took the SCN out of genetically abnormal hamsters, which had a circadian rhythm of 20 hours, transplanting it into normal 24 hour hamsters, finding their circadian rhythm decreased to 20h
what are exogenous zeitgebers?
cues from the environment that play an important role in regulating time
-combine with endogenous pacemakers to regulate the body clock so an individual is synchronised with the environment (eg sunlight)
what is entrainment?
-when there’s an adjustment of the body clock in line with the environment, eg moving time zones
research on exogenous zeitgebers
-steel et al 2008 - monitored 6 ps in total isolation in the arctic for 6 weeks to investigate affects of constant daylight, ps kept sleep logs, found 5/6 developed a free-running sleep/wake cycle of 24+h, but they were all individual with no patterns, meaning social cues may not have a strong affect in the absence of other zeitgebers
evaluate circadian rhythm
-much research lacks external validity, (artificial conditions)
-monitoring sleep could have an affect on it, rather than the zeitgebers/pacemakers
-extrapolation issues (psychological differences)
what are infradian rhythms
more than 24 hours, eg menstrual cycle
-not imposed purely by the release of hormones
-suggest zeitgebers such as light and odours are also involved
-also eg hibernation
research on infradian rhythms
-McClintock + Stern - when women received odourless compounds from women in the latter half of their cycle, their menstrual cycle shortened, presumable because of the effect of the other woman’s hormones, suggesting it can be altered by communication via pheromone
evaluate infradian rhythms
-effect of pheromones helps explain menstrual synchrony, something in the shared environment that acts as a zeitgeber
-possible evolutionary advantage, eg synchronised pregnancies so childcare can be shared
-extent to which pheromones have effects is unclear, still requires research
-wilson - results from menstrual synchrony research fell within chance factors so isn’t significant
what are ultradian rhythms?
-less then 24 hours
-sleep/wake cycle
-sleep has 5 stages, length of which depends on age
-stage 1>2>3>4>3>2>5
stage 1 of the sleep wake cycle
-5-15 min
-less brain activity than relaxed wakefulness but more than other stages (apart from rem)
-heart rate slows, muscles relax, people are easily woken
stage 2
-5-15 min
-sleep spindles occur
-body continues to relax, still easy to wake
stage 3
-5-15 min
-less sleep spindles
-slow delta waves
-body relaxes more, harder to wake
