1. Biological Rhythms
These are patterns of activity in animals and plants
Circadian (24 hours)
Infradian (more than 24 hours)
Ultradian (less than 24 hours)

2. Biological Rhythms There are hundreds of biological rhythms in humans:
Sleep/wake cycle
Sleep
Hormone production
Menstrual cycle
Core body temperature

3. Circadian Rhythm A biological rhythm with a periodicity of one day.
Periodicity = time between peak and next peak
Sleep/wake
Hormone production (some)
Core body temperature
Pain sensitivity

5. What gives us our sense of time?
Exogenous Zeitgeber
Outside the body
External cues
(e.g. your alarm clock)
Environmental stimuli
(e.g. daylight, temperature change)
Social cues
Endogenous Pacemaker
Within the body
Specific bio-chemical changes
(e.g. melatonin, SCN, pineal gland)
The activity of these pacemakers
Is likely to be innate
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6. The Master!
Suprachiasmatic nucleus
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7. Suprachiasmatic nucleus
This is the main endogenous pacemaker in mammals
Located above optic chiasm
Information about light and dark hits retina
This information goes to SCN
Then to pineal gland
This produces melatonin
Induces sleep
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8. Endogenous Pacemakers
small cluster of cells in our hypothalamus called the: Suprachiasmatic nucleus (SCN).
linked to our visual system
influenced by the amount of light we detect.
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9. 24 Hours of Melatonin Secretion
What does the graph tell us about melatonin production?
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10. Michel Siffre Study
Spent 6 months in a Cave with free running endogenous pacemakers.
He could ask for lights to be switched on and off.
Researchers monitored bodily functions.
At first circadian rhythm was erratic but his sleep wake settled into a 25 hour cycle. His core body temperature also lengthened.

11. Siffre Sleep wake became out of sync with other circadian rhythms.
Findings
Sleep wake became out of sync with other circadian rhythms.
Psychological disruption

12. Other research into Circadian Rhythms

13. Infradian Rhythms
A biological rhythm that has a periodicity of more than one day.
Menstrual cycle
Hibernation
SAD
Testosterone production in hamsters

14. Sleep Wake Cycle Sleep Hormone production Hibernation
Starter
Sleep Wake Cycle
Hibernation
The Menstrual Cycle
Sleep

15. Exam Question
Sam is a police officer. She has just started working the night shift and after a week, she finds she has difficulty sleeping during the day and is becoming tense and irritable. Sam is also worried that she is less alert during the night shift itself.
Using your knowledge of endogenous pacemakers and exogenous zeitgebers, explain Sam’s experience (4)

16. Answer
An endogenous pacemaker is an internal mechanism that controls circadian rhythms such as the sleep wake cycle. (1) Exogenous zeitgebers, such as light, are external factors that influence circadian rhythms. (1) As Sam has recently moved to a night shift, her biological rhythm of sleep is out of sync with the external cues, that is, she is trying to stay awake in the absence of light and go to sleep when exogenous zeitgebers are telling her to be alert and active. (1) Shift work can lead to disrupted sleep patterns, increased anxiety, decreased alertness and focus. It is particularly difficult to stay awake when our core body temperature is at its lowest, around 4 am. (1)

17. Ultradian Rhythms
A biological rhythm with a periodicity of less than one day
Transition between SWS and REM
Food seeking behaviour
BRAC

20. Real Life Support Miles et al (1977) studied a man blind from birth
He had a 24.9 hour
Circadian rhythm
Used stimulants and
sleeping tablets to try and
fit in with the 24 hour clock
Sedatives
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21. Evaluation Practical applications
Alstadhaug et al (2008) found migraine attacks have a circadian rhythm with peaks in attacks at midday
Also that changing the clocks affected larks and owls differently and that overall both changes had negative effects on mood and behaviour
Biological determinism
Actually there is research that shows that if you are
told you have to wake up earlier than usual it can
effect your stress hormones such as cortisol levels.
born et al (1999) found higher ACTH in P’s than
normal at the time they told they must rise.
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22. Objectives
To be able to describe what is meant by an infradian rhythm.
To be able to outline and evaluate research into infradian rhythms.
To be able to discuss practical applications of research into infradian rhythms

23. Seasonal Affective Disorder (S.A.D.)
Lack of daylight
Increases melatonin
Fatigue
Disordered sleep patterns
Risk of depression
Treated with UV light and/or melatonin therapy.
For more info follow the link:
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24. Research (SAD)
Egrise et al (1986) found we have lower levels of seratonin during the winter months
Norway with prolonged periods of winter darkness have higher frequency of SAD
Magnusson and Stefansson (1993) did not find this pattern
Terman (1988) found SAD 10% in northern USA and only 2% in Florida
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25. Real World Applications
Use of high Lux bulbs that mimic natural daylight have been shown to reduce fatigue, depression and lethargy in SAD sufferers.
However, this may be because sufferers expect the treatment to work
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26. Exam Question Describe one ultradian rhythm (5)
What is an ultradian rhythm?
Why is sleep an ultradian rhythm?
What are the stages of sleep?
Emphasise the difference between NRM and REM.