The Sleep Wake Cycle -
- We normally feel sleepy when it gets dark and are awoken by sunlight. Or our cycles are goverened by knowing the time of day.
- Sunlight etc are external cues, important in guiding sleep wake cycle.
- Internal (endogenous) clock is free running and sets a cycle of about 24-25 hours.
- Internal clock does not work alone.
- External cues help to adjust the internal clock to the envirroment you live in.
- Circadian Rhythms persist despite isolation from day light (shows existance of internal clock).
Core Body Temperature -
- One of the best indicators of circadian rhythms.
- Lowest at 4:30am (36 degrees) and highest at 6:00pm (38 degrees).
- Slight through after lunch, due to effects of eating lunch and people not eating lunch.
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Sleep Stages -
- Daily Cycles of wakefulness and sleep follow circadian rhyhms.
- There are five stages of sleep.
- First four stages are called NREM (non rapid eye movemet) and the fifth stage is called REM sleep (rapid eye movement), so called because of the movements of the eye when sleeping.
- One sleep cycle goes through all five stages and lasts about 90 mins.
- Stages 1 and 2 are light sleep, electrical activity in brain. Brain produces typical pattern called beta wave. More relaxed you feel, brain waves slow and have greater amplitude (alpha wave). As you fall asleep, waves slow even more and have greater frequency (theta wave).
- Stages 3 and 4 are even slower delta waves. These stages are known as SWS (slow wave sleep) Hard to wake someone at this stage. In deep sleep, physiological repair is undertaken such as production of gowth hormone.
- REM Sleep is fast desyncronised EEG activity resembling awake brain.
- These cycles contine throughout the night, where SWS period gets shorter and REM period gets longer.
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Monthly Cycles -
- The female menstural cycle is the most obvious monthly cycle.
- Pituatry gland releases hormones (folicile stimulating hormone) and (luteninsing hormone) which stimulate a folicile release of female hormone oestrogen. When egg has ripened, the rupture folicile secretes progesterone and causes lining of womb to prepare for pregnancy by increasing blood supply. Two weeks after ovulation, if there is no pregnancy, progesterone is reduced and causes lining of womb to shed.
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Circadian Rhythms cont.
- Hormone productuon follows ciracidan rhythm.
- Cortisol is lowest at midnight and peaks around 6:00am (cortisol is produced when stressed).
- Cortisol is related to making us feel alert when we wake up.
- Hence, why waking at 4:00am we cannot think clearly (cortisol levels are insufficant).
- Melatonin and Grotwh Hormone have clear circadian rhythms and both peak around midnight.
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