Make sure you remember the Key Concepts

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Clarissa Pitts
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1 A2 Psychology Term 1 Module 4 Physiological Psychology Biological Rhythms, Sleep and Dreaming Area of Study: Biological Rhythms. Lesson 7 Getting you Thinking pg 403 Make sure you remember the Key Concepts Why do we sleep? Recovery from stress Rest Thermoregulation Protection from infection sleep deprivation results in a small reduction of immune system efficacy Restoration growth and repair

2 Bodily Rhythms Obvious ones Menstrual cycle Sleeping and waking Less obvious Variations in body temperature Algae Squirrels Animal rhythm examples Rhythmic activities are endogenous (in built) Endogenous pacemakers External events exogenous zeitgebers (external timegivers Much of research focused on the relationship between endogenous (internal) pacemakers and exogenous (external) zeitgebers. Different Types of Biological Rhythm Circadian rhythm Infradian rhythm Ultradian rhythm

3 Circadian Rhythm From Latin words about and day 24 hour rhythm Body temperature peaks in late afternoon, lowest during early hours Mammals exhibit about 100 (Green 1994) Synchronise behaviour and body states to changes in the environment Light and dark has implications for survival Nocturnal animals avoid day predators Diurnal animals adapted to forage for food during day. Endogenous pacemaker (biological clock) anticipates the onset of light or darkness. Infradian Rhythms Occur less than once a day e.g. hibernation Menstrual cycle Some are yearly circannual rhythms Migration in birds Hibernation Often driven by exogenous factors e.g. food availability, but seasonal fluctuations in body weight occur accordingly in lab. conditions. Show rhythms of about 365 days, even in absence of external zeitgebers suggests existence of endogenous circannual biological clocks, sometimes free running bio. rhythms

4 Research into circannual rhythms Research on ground squirrels showed that lesions in the suprachiasmatic nucleus disrupted circadian activity cycles. BUT they had no effect on circannual rhythms, like body weight or reproduction. Thus circannual rhythms must have a different underlying mechanism i.e. a different endogenous pacemaker/bio. clock. S.A.D Seasonal Affective Disorder Seasonal change In winter a low period may become profound depression. Symptoms include; slow movement, sleep a lot and overeating. In summer there may be mania (Blehar & Rosenthal). Elated, energetic and thinner Deferring opinions that northern latitudes have more sufferers (Magnusson & Stephansson 1993) Light S.A.D. cont. Suppresses melatonin, sleep regulating hormone Exposure to darkness stimulates melatonin synthesis SAD sufferers have high threshold for melatonin suppression. Therapy involves exposure to bright white light for an hour a day Serotonin may also play role as it has a seasonal rhythm, with lower levels in winter and spring.

5 Ultradian rhythms More than one complete cycle in 24 hours Sleep in one of these as it oscillates between stages of lighter and deeper sleep during a single night, each cycle last about 90 minutes Other ultradian rhythms include; feeding and hormone release. Those found in complex behaviours, e.g. alertness. Lesions in specific areas of hypothalamus affect ultradian rhythms Periods of rhythm are correlated with brain and body size, e.g. smaller animals have more rapid cycles (Gerkema & Dann 1985) Endogenous pacemakers & Exogenous Zeitgebers Inherited genetic mechanism, embryos But must respond to exogenous zeitgebers if to fully co-ordinate with outside world Most influential is light Role of Pineal Gland Most important endogenous pacemaker/bio clock Contains light receptors Light influences activity of neurons in pineal gland Such neurons have natural rhythmic activity and convert serotonin to melatonin. Released melatonin acts on organs and glands and appears responsible for rhythmic nature of activities, e.g. action on brainstem helps synchronise sleeping and waking phases.

6 Role of Pineal Gland, evidence Melatonin produces sleep in sparrows Abraham 2000) Chickens wake as dawn breaks and melatonin secretion falls (Binkley 1979) Although waking is controlled by bio. clock in pineal gland it is adjusted by light to daybreak, which varies. Role of suprachiasmatic nucleus (SCN) Is small area in hypothalamus Is biological clock Its neurons have built in circadian rhythm firing pattern It regulates manufacture and secretion of melatonin in pineal gland Role of suprachiasmatic nucleus (SCN) cont. Is connected to the eye retina Light falling onto retina influences activity of SCN neurons and therefore the release of melatonin. Link with light always maintained. Recently found that light applied to the backs of knees could shift circadian rhythm in temperature and melatonin secretion (Campbell & Murphy 1998) Pineal gland and SCN function jointly as endogenous pacemakers

7 SCN role in infradian rhythms Hamsters show increased testosterone secretion as days lengthen. Lesions of SCN destroys this cycle and testosterone is produced all year round Probably because the daily light levels are perceived as being longer than 12 hours so therefore it must be summer Removing exogenous zeitgebers Despite endogenous nature of pineal gland and SCN they are synchronized with light/dark cycle of outside world. Studies have been done on the effect of removing light so the bio. clocks run free. Research into free running rhythms Michael Siffre spent 6m underground Bodily functions were recorded When awoke lights on When went to bed lights off Cycle settled to hours, slightly longer than 24 usual. Similarly Aschoff & Weber found a hour free running cycle

8 Homework Notes on Evaluation AO2 Read Consequences of Disrupting Biological Rhythms and take your own notes for class discussion on it next time. Use the blank slides to help you. Then note the evaluation on page 408 Check Revision summary Check your understanding for quick test next lesson.

Circadian rhythm and Sleep. Radwan Banimustafa MD

Circadian rhythm and Sleep. Radwan Banimustafa MD Circadian rhythm and Sleep Radwan Banimustafa MD Homeostasis Maintenance of equilibrium by active regulation of internal states: Cardiovascular function (blood pressure, heart rate) Body temperature Food