Circadian, Ultradian and Infradian Biological Rhythms Circadian, Ultradian and Infradian

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)

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.’

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

Circadian rhythms

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.

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

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

Questions I have….

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

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

Monthly rhythms – menstrual cycle

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)

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

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 90-100 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

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. 10.30am coffee break, cat naps in the afternoon

Questions I have…

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

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

Questions I have …

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