Biological Rhythms

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Ultradian rhythms- rhythms that occur more than once a day.   E.g. alertness, sleep stages and metabolism.   Stages of sleep. Shallow sleep where there is a reduction in heart rate, muscle tension and body temperature. EEG scans show alpha waves. In this stage you can still be easily awakened by stimuli like noise. EEG scans show Theta waves with sleep spindles which is the brains response to external stimuli. This stage lasts for about 20 minuets. In this stage, sleep is deeper with heavy breathing. EEG scans will show Delta waves Slow wave sleep (SWS)- is deep sleep were it is hard to be woken from. The body temperature has dropped. This is the stage were sleepwalking will occur. EEG scans show Delta waves. This is REM sleep, where it is even harder to be woken from. Brain activity is high as when we are awake (Bata waves). This is when dreaming occurs.   These stages are repeated thought the night going from 1,2,3,4,5,4,3,2,3,4,5 e.t.c.  

REM sleep and dreaming.


Aserinsky and Kleitman (1995)- first discovered the association between REM sleep and dreaming.

Dement and Kleitman (1957)- between 70-75% of participants woken in REM sleep reported dreaming.

Green (1994)- 30% of sleepers in SWS reported dreaming.

Circadian rhythms.

- rhythms that occur every 24 hours.

E.g. sleep/wake cycle and body temperature.

SCN is an endogenous pacemaker in controlling the level of sleep. This process starts with light entering the eyes, even when they are shut. This information is sent via neural pathways to the SCN which is located in the hypothalamus. the information is then sent again thorough neural pathways to the pineal gland. This is located deep within the brain. The low light information from the SCN triggers the pineal gland to release melatonin. The levels of melatonin rise in the blood which makes us sleep.

Exogenous zeitgerbers.

Miles et al (1977)- studied a man who was blind from birth and had a sleep/wake cycle of 24.9 hours. He had to adjust his cycles with stimulants and sedatives as his natural cycle was 25 hours. This shows that light is the main exogenous factor.

Luce and Segal (1966)- people who lived in the Arctic circle sleep for 7 hours per night despite the fact that the summer sun never sets. This shows that light is not the only Zeitgerber nor is the biological clock the only by light. Other influences like motivation and social customs are also important.

Endogenous pacemakers .

Siffre (1972)- he spent 6 months in a cave in Texas cut off from all exogenous stimuli. He was able to turn the lights on and off and eat whenever he wanted. After a period of time his sleep wake cycle became 25 hours.

Morgan (1995)- removed the SCN from hamsters and found that their circadian rhythms diapered.

Ralph et al (1990)- breaded mutant hamsters with a 20 hour sleep/wake cycle, then transplanted the SCN of the mutant hamsters into normal hamsters. The normal hamster then




Good, but it could be set out a little better.

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