1. Circadian, Ultradian and Infradian
Biological Rhythms
Circadian, Ultradian and Infradian

2. Lesson objectives To introduce you to the biological rhythms
Define the 3 types (A01)
Consider and note some examples of each (A02)
Develop your research bank of studies
Update checklists
Make use of the research and consider at least 2 evaluation points for each rhythm (A03)

3. Biological Rhythms
Body rhythms are biological processes that show reoccurring variation over time…ranging from hours to years and reflect the influence of the earths rotation upon us… it's living inhabitants, along with plants and animals.
Biological Rhythm - ‘Any change in a biological activity (such as sleep and waking) that repeats periodically.’

4. Biological rhythms…
repeated changes in the way that biological system behave
Evolved responses to environmental cycles – day/night, summer/winter

5. Circadian rhythms

6. Circadian rhythms lasts about 24 hours
Highlight the key words
lasts about 24 hours
A pattern of behaviour that occurs/reoccurs every 24 hours which is set and reset by environmental light levels
circa (about) diem (a day)
The purpose is to optimise an organism’s physiology and behaviour to best meet the varying demands of the day/night cycle
This cycle is controlled by a ‘biological clock’ (endogenous pacemaker) but is also influenced by external cues (exogenous zeitgebers) such as light.
Any cycle that lasts about 24 hours
A pattern of behaviour that occurs/reoccurs every 24 hours which is set and reset by environmental light levels
The word circadian - circa (about) diem (a day)
The purpose of CR?
Optimise an organism’s physiology and behaviour to best meet the varying demands of the day/night cycle
This cycle is controlled by a ‘biological clock’ (endogenous pacemaker) but is also influenced by external cues (exogenous zeitgebers) such as light.

7. Some examples… Sleep wake cycle Heart rate Metabolic rate
Breathing rate
Body temperature
Hormone concentrations can vary over the course of the day – e.g. in women, prolactin, hormone that stimulates milk production, peaks at night
Breathing rate max value in late afternoon and min in early morning

8. Michel Siffre – ‘free-running’ circadian rhythms
QUESTION: What if we took away exogenous zeitgebers and let out bodies ‘free run’?
Michel Siffre – ‘free-running’ circadian rhythms
Michael Siffre (1962)
Testing internal body clock
Spent 61 days and nights underground in a cave
No exogenous zeitgebers (lights, clocks, radio etc)
Only influence was endogenous pacemakers (internal body clock)
Emerged 17th Sept, thought it was 20th Aug
Natural rhythm extended to over 24 hours
Supports endogenous
real-world application

9. Questions I have….

10. Infradian rhythms - occur over a period of 24 hours
- Weekly rhythms – sexual activity in humans, births in humans, seven day rhythms for blood pressure and heart rate
- Monthly rhythms - Menstrual cycle
- Annual rhythms – SAD and seasonal variation in mood, increased rate of heart attacks in winter, most deaths occur in January

11. Weekly Rhythms Male testosterone higher at weekends
Young couples report more sexual activity at weekends
Frequency of births is lower at weekends
Halberg et al (2002) reported seven day rhythms of blood pressure and heart rate

12. Monthly rhythms – menstrual cycle

13. Annual Rhythms In animals – related to seasons e.g. migration
In humans – not just related to changes in temperature
e.g. seasonal variation in mood (especially in women) (Magnusson 2000) with some people being extremely depressed in the winter months (SAD – research this further – PHG has lots more info on it)
Winter also associated with increase in heart attacks
Annual rhythm of human deaths – most occurring in January (Trudeau 1997)

15. Ultradian rhythms
- shorter than 24 hours
- Sleep/wake cycle
- BRAC – Basic Recovery Activity Cycle – we move through states of alertness and fatigue

16. Utradian Rhythms – sleep cycles
EEG - electroencephalogram
Utradian Rhythms – sleep cycles
The UR in human sleep follows patterns of alternating REM and NREM sleep which consists of stages 1-4 before going into stage 5 of REM sleep
The cycle repeats itself every minutes throughout the night
Measuring electrical activity in the brain – each stage shows a distinct EEG pattern
It’s during stage 5 – REM sleep – that the brain patterns look most similar to that of an awake person

20. Basic Rest Activity Cycle (BRAC)
Does anyone have a nap during the afternoon? Do you feel you are more tired at certain points in the day?
Basic Rest Activity Cycle (BRAC)
Kleitman (1969) referred to the 90 minute cycle found in sleep as the BRAC
He also suggests that this 90 minute cycle occurs through the day – we move from a state of alertness to a state of fatigue
Research states the human mind can concentrate for up to 90 minutes but towards the end we lose concentration, get hungry and tired – we run out of resources
Daytime BRAC isn’t as obvious as the sleep cycle but everyday observations show it’s existence e.g am coffee break, cat naps in the afternoon

21. Questions I have…

22. Exogenous Zeitgebers and Endogenous Pacemakers
Exogenous – anything outside the organism
German – zeit and gerber = time giver
Biological rhythms like the ones mentioned must be constantly fine-tuned in order to stay in harmony with the external world.
Endogenous pacemakers, sometimes referred to as internal biological ‘clocks’, and
Exogenous (or external) zeitgebers, which reset this clock every day to maintain its coordination with the external world

23. E.G of an endogenous pacemaker influencing sleep/wake cycle :
E.G of an exogenous zeitgeber influencing sleep/wake cycle:
Light: This is the key zeitgeiber and Social cues
E.G of an endogenous pacemaker influencing sleep/wake cycle :
Suprachiasmatic Nucleus (SCN), which lies in the hypothalamus

24. Questions I have …

25. Todays key terms: Circadian (24hrs) Ultradian (less than 24hrs)
Infradian (more than 24hrs)
Weekly cycles (testosterone / blood pressure)
Monthly cycle (menstruation)
Annual cycles (SAD)
BRAC
Sleep wake cycle
Endogenous pacemaker
Exogenous zeitgeber