biological rhythms Flashcards
circadian, infradian and ultradian and the difference between these rhythms. The effect of endogenous pacemakers and exogenous zeitgebers on the sleep/ wake cycle.
what is an endogenous pacemaker?
endo=inside genous=producing
internal body clocks that keep biological processes in time e.g. suprachiasmatic nuclei
what is an exogenous zeitgeber?
exo=outside zeitgeber=timegiver
external cues that entrain internal body clocks meaning altering body clocks to match the environment e.g. light
what is a circadian rhythm?
biological rhythm that lasts around 24hrs
examples of circadian rhythms?
sleep-wake cycle
release of hormones
body temp
blood pressure
how do EPs and EZs control circadian rhythms?
EPs are internal body clocks that keep the pattern of circadian rhythm
whereas EZs like light and jet lag may counter EPs
EP will be entrained by the EZs to the new time zone but it can take several days
what is the suprachiasmatic nucleus (SCN)?
SCN is the endogenous pacemaker for the sleep-wake cycle aka the master clock
part of the hypothalamus within the limbic system
located at the optic chiasm (where the optic nerves cross)
when light is detected by the SCN it sends light to the pineal gland which stops the production of melatonin
what is the role of light in the sleep-wake cycle?
light is the primary EZ in the sleep-wake cycle
social cues e.g. when we time our meals, exercise, go to bed or environmental cues e.g. clocks are thought to act as EZs
explain a study into circadian rhythms
Siffre (1975)
aim: investigate whether the EP for the sleep-wake cycle is free running and whether a predictable cycle would be maintained without constant entrainment by EZs
method: Siffre spent 179 days in a cave with no natural light or other potential EZs like clocks or social cues
results: Siffre’s body clock (EP) maintained a regular cycle of around 25 hours without EZs
conclusion: suggests the EP for sleep-wake cycle is free running but needs entrainment to keep to the 24hr day-night cycle
evaluation of Siffre’s cave study
- criticised use of artificial light in isolation experiments on the sleep-wake cycle suggesting the artificial lights disrupted measurements of the free-running circadian rhythm by acting as an EZ
+ Czeisler controlled artificial light and found the circadian rhythm was closer to 24 hrs with little drift
explain a study into light as an EZ
Vetter (2011)
aim: to investigate light as an EZ
method: 27 office workers were exposed to strong blue light - found that they would shift their circadian rhythm to match office lighting
compared to control group of 27 office workers with normal office lighting - found that rhythms matched the shifting time of the natural light of dawn
conclusion: suggests that light is an EZ and artificial lights can disrupt the EP by over-riding the primary EZ of natural light
explain a study into SCN is EP
Ralph (1990)
aim: to investigate SCN as an EP
method: hamsters with the Tau mutation have a circadian rhythm of 20hrs compared to 24hrs for normal hamsters
the SCN from normal hamsters was transplanted into the brain of Tau mutant hamsters and vice versa
results: tau hamsters gained a sleep-wake cycle of 24hrs and normal hamster gained a 20 hr cycle
conclusion: suggests SCN is the main EP in the sleep-wake cycle
evaluations of circadian rhythms
+ understanding how EZs affect the sleep-wake cycle can help psychologist find treatments for jet lag (for people that travel for work) and shift work (positive effect on economy)
+ understanding the circadian blood pressure rhythm can help with timing drug treatments and health treatments
+ knowing psychological effects of exposure to blue light has implications for phone usage late at night which provides people with advice on how to maintain a healthy sleep pattern
+ light is the main EZ and social cues are less effective - research on a man blind from birth showed that even with social cues the blind man had a 24.9 sleep-wake cycle - his sleep was out of synch with the rest of society
+ evolutionary explanation for the sleep-wake cycle as humans are not specialised for night time activity so we have a sleep period at night to protect us from accidental harm and predation
