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Carleton University
PSYC 2800
Amanda Helleman

Lecture # 1n *final+ Why Do We Sleep and Dream? • Origins of Biological Rhythms • Biorhythm: Inherent timing mechanism that controls or initiates various biological processes • Many aspects controlled by bio rhythms (eating, sleep, exercise) – Linked to the cycle of days and seasons produced by the Earth’s rotation around the sun – Animals living near the poles of the Earth are more affected by seasonal changes than animals living in equatorial regions – Human behavior is governed more by : daily cycles than by : seasonal cycles – We breed all year round, not just at given times of the year • Biological Clocks • Behavior is not simply driven by external cues from the environment • Rhythms are endogenous (control comes from within) – Biological clock: Neural system that times behavior. • Allows animals to anticipate events before they happen – Example: Birds migrate before it gets cold. Internal cue to get going. • Biological Rhythms • Period: – Time required to complete a cycle of activity – Ex: A day, one sleep wake cycle for humans • Circannual: Rhythm – Yearly (e.g., migratory cycles of birds) • Infradian: Rhythm – Less than a year (e.g., human menstrual cycle montly, also known as lunar cycle) • Circadian: Rhythm – Daily rhythms (e.g., human sleep cycle) – Peak in BP first thing in the morning, bowel morning usually in the morning, testosterone highest in morning, alertness highest in morning (based 8 am, 10 pm cycle). Body temp., highest in evening. Body temp. related to when you eat. • Ultradian: Rhythm – Less than a day (e.g., eating cycle) • Free-Running Rhythm: Rhythm of the body’s own devising in the absence of all external cues – Without input from external cues, our bodies have their own rhythms with periods of 25 to 27 hours • Sleep-wake cycle shifts an hour or so everyday – Animals expand: and contract: their sleep periods as the sleep- related lighting period expands or contracts Zeitgebers: Environmental event/external cue that entrains biological rhythms; a “time giver” – Example: light resets biological rhythms • Entrainment – Determination or modification of the period of a biorhythm • Jet Lag: Fatigue and disorientation from rapid travel through time zones an exposure to a changed light-dark cycle • Easier to fly east to west, only need to stay up later instead of wake up earlier. • Neural Basis of the Biological Clock • Suprachiasmatic Nucleus (SCN) *within hypothalamus+ – Main pacemaker of circadian rhythms located just above the optic chiasm • Retinohypothalamic Pathway *important in sleep/wake cycle+ – Neural route from a subset of cone receptors in the retina to the suprachiasmatic nucleus of the hypothalamus; allows light to entrain the rhythmic activity of the SCN – Why people have seasonal affective disorder. Can’t retrain to new time in winter and get depressed. Related to melatonin (main hormone of SCN). All they want to do is sleep but can’t so affects mood. • Other pacemakers exist in the retina and pineal gland, but the SCN is the main one • Immortal Time • Lesion SCN, bio rhythms removed • Endogenous rhythm is not learned – Martin and colleagues: transplantation studies in hamsters • After lesions to the SCN, eat and sleep a normal amount, but the rhythmic nature of these behaviors disappears • Ex: Eat same amount of calories but not 3 meals but all over the place • If SCN cells from embryos are transplanted back into the lesioned animals, they will reestablish circadian rhythms • Neural Basis of the Biological Clock What Ticks? • What is SCN doing to create these bio rhythms • At least half a dozen genes and the proteins they make seem to produce the circadian rhythm of SCN cells in mammals • Mechanism is not fully understood • Pacemaking Circadian Rhythms • Model for Circadian Timing System – Light entrains the SCN pacemaker – SCN pacemaker drives a number of “slave oscillators,” each of which controls the rhythmic occurrence of one behavior/.circadian function (e.g., body temperature) – SCN pacemaker may drive the slave oscillators via hormones, proteins, or neurotransmitters • Pacemaking Circannual Rhythms • Melatonin : Critical hormone secreted by the pineal gland during the dark phase of the day-night cycle; influences daily and seasonal biorhythms • Signaling molecule • We have peaks in troughs in the level of this hormone – Example: Hamsters • In winter: Days shorten. Melatonin levels increase, gonads shrink, testosterone levels decrease, and sexual behavior decreases • In summer: melatonin levels decrease, gonads grow, testosterone levels increase, and sexual behavior increases • Similar with birds and singing to attract mates • Sleep Stages and Dreaming Measuring How Long We Sleep • There
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