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

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

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

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.

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

Research 1. Siffre (1962) supported by Aschoff and Wever (1976). Participants in a bunker with no natural light but could turn on lights. = extended circadian cycle. 2. Folkard et al (1985) Participants had no light for three week. Gave time cues for 22 hours day. Only one participant adjusted to this 4

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 Bio Rhthyms Unit 4

The Master! Suprachiasmatic nucleus Bio Rhthyms Unit 4

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 Bio Rhthyms Unit 4

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. Bio Rhthyms Unit 4

Exogenous Zeitgebers These are external cues that can adjust our natural biological rhythm. They include Light- this is the most important EZ that is known to influence the SCN and so the sleep/wake cycle. Temperature Social cues (other people)

Research that can be used Morgan (mutant hamsters) supports the role of EP. Decoursey (chipmunks) supports the role of EP. Siffre shows the importance of EP to maintain a regular clock but also the role of light in resetting the clock to 24 hours (a blended system)

Questions Outline and evaluate research into circadian rhythms (16) Discuss the role of endogenous pacemakers and exogenous zeitgebers (16)

24 Hours of Melatonin Secretion What does the graph tell us about melatonin production? Bio Rhthyms Unit 4

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)

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)

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

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: http://hcd2.bupa.co.uk/fact_sheets/html/sad.html Unit 4 Bio Rhthyms

Research (SAD) Egrise et al (1986) found we have lower levels of serotonin during the winter months. When there is less light there is less serotonin and more melatonin. This suggests that a lack of serotonin in the winter months is a contributory factor to SAD. However, not everyone suffers from this disorder suggesting a genetic predisposition. Bio Rhthyms Unit 4

In Norway with prolonged periods of winter darkness have higher frequency of SAD Magnusson and Stefansson (1993) did not find this pattern. Therefore, this pattern is not a reliable result. However, in Norway children are often treated with light therapy in the winter months. Terman (1988) found SAD 10% in northern USA and only 2% in Florida

The menstrual cycle 28 day cycle controlled by hormones oestrogen and progesterone.

Research into the Menstrual cycle See handout – Russel and mcClintock research on synchrony by proximity.

Questions Discuss infradian rhythms (16) Discuss research into infradian rhythms (16) Outline one infradian rhythm (4)

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

Activity Read the article on sleep. Fill in the worksheet on the stages of sleep. How well have you learnt this ABC (D) or AB and CD Bio Rhthyms Unit 4

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 Bio Rhthyms Unit 4

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. Bio Rhthyms Unit 4

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

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 Bio Rhthyms Unit 4

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.