Circadian Rhythms Flashcards
Core body temperature
Body temp is lowest at 4.30 am and night at 6.00 pm
There is a post lunch dip due to the effects of eating where you become tired in the afternoon but it occurs even if you haven’t eaten
Hormones
Cortisol levels are lowest at midnight and peak at 6 am. When levels are high, this creates alertness which explains why you can’t think clearly when you wake up earlier than usual.
Melatonin and growth hormone levels peak at midnight
The sleep-wake cycle
External cues tell us when to go to sleep such as darkness or the time on a clock
Free-running cycle maintains the sleep wake cycle in the absence of external cues. It is governed by an internal clock
The sleep wake cycle can be entrained to some extent by external cues
Ao2 the sleep wake cycle
Aschoff and wever placed ppts in an underground ww2 bunker with no external cues and found ppts cycle was between 24-25 hours but some were as high as 29 hours. This demonstrates the existence of endogenous pacemakers as their cycle persisted without exogenous zeitgebers. But it also highlights importance of external cues as their internal clocks weren’t accurate without them. LOW ECO DUE TO LAB SETTING as can’t be generalised to real world setting. Sample was small meaning generalisation is hard. Ppts were volunteers.
Michel siffre spent 6 months in a cave without external cues and found his sleep wake cycle was generally 24 hours but sometimes it dramatically changed to 48 hours. This highlights existence of an internal circadian clock. Also highlights importance of exogenous zeitgebers in maintaining internal biological clock as his rhythm wasn’t always 24 hours. SINGLE CASE STUDY so hard to generalise due to insdividual differences. Age may affect results as other studies have shown sleep patterns vary among age groups. Artificial lighting was used and that may be a confounding variable. CZIESLER ET AL showed that rhythms could be entrained using artificial lighting. So the studies could lack external validity to others as well as low internal validity as it isn’t measuring what it set out to measure. Siffre used an experimental approach and so he could demonstrate a causal relationship between external cues and sleep-wake cycle.
Ao2 core body temp
Folkard et al looked at the learning ability of 12 and 13 year old children who had stories read to them at either 9 am or 3 pm. After one week, the afternoon group showed better recall and comprehension which suggests long term recall is best when body temp is highest.
Gupta found that performance on iq tests was best at 7 pm as compared with 9 am or 2 pm which might be an important consideration when taking exams.
IDA
Understanding circadian rhythms has real world applications particularly in the field of chronotherapeutics. This is the study of how timing affects drug treatments. The circadian rhythms affects digestion, heart rate, hormone secretions and other functions which all need to be taken into account when taking drugs. For instance, medication that is taken when the target hormone is low may have no effect but more effective when taken when the hormone is high.
