Ez and EP recap

(bullet point key terms) Evaluation points (including I&D) Starter / capture Rhythm (bullet point key terms) Research Evaluation points (including I&D)

Lesson Objectives To understand (explain), apply to (explain) examples evaluate (discuss) the impact of endogenous pacemakers and exogenous zeitgebers.

Endogenous vs Exogenous Endogenous Pacemakers.... Part of the internal organism. Internal body clocks that regulate biological rhythms such as the sleep wake cycle. Exogenous Zeitgebers.... External cues in the environment that may affect our biological rhythms. E.g. the influence of light on the sleep/wake cycle.

The Suprachiasmatic Nucleus (SCN) In mammals, the main endogenous pacemaker is a pair of tiny clusters of nerve cells called the SCN, which lie in the hypothalamus, just above the optic chiasm (where the optic nerves from each eye cross over)

Endogenous Pacemakers Even when our eyes are shut the SCN gets info on light from the optic nerve. Light can penetrate the eyelids and special photoreceptors in the eye transfer light signals to the SCN. If our endogenous clock is running slow – the morning light automatically shifts the clock ahead so it is in synchrony with the world outside

Light, the pineal gland and melatonin regulate the sleep-wake cycle Another endogenous pacemaker that works with the SCN is the Pineal Gland. Contains light sensitive cells. When light is sensed melatonin production is inhibited. When light level falls melatonin production increases This induces sleep by inhibiting brain mechanisms that promote the awake state. Light, the pineal gland and melatonin regulate the sleep-wake cycle

Melatonin Secretion asleep Melatonin Level 7 am 7 pm 7 am Time of Day

Animal Studies and the SCN Decoursey et al (Chipmunks) Morgan et al (Hamsters)

Now for Exogenous Zeitgebers… Exogenous = outside the organism Zeitgeber = time-giver The biological-clock is reset each day by cues in the environment – like the light cues of sunrise and sunset. This process is called entrainment, (the opposite of free- running where the biological clock works free of any exogenous cues, including social cues like clocks).

Now for Exogenous Zeitgebers… What has this got to do with it? https://www.youtube.com /watch?v=pO5Tcr3OpC8 Light! Summarise how light is an exogenous zeitgeber…

How do you train a baby to sleep? So imagine for a second, you’ve just had a baby and all it does is cries. You are desperate for some sleep. How do you train it to sleep at normal times? Social Cues! In infants the sleep/wake cycle is initially random but by 6 weeks the circadian rhythms begin and by 16 weeks most babies are entrained. Why? Schedules and social cues determined by the parents – e.g. meal times and bed times. This is also applied to adults. Rather than responding to hunger and fatigue, conforming to local times for sleeping and eating will train your circadian rhythm (good for jet lag!)

Evaluate (A03) Colour code or sort the effective evaluation points. (Point, Explain/Evidence, Link) NB: The term “peripheral oscillator” refers to a circadian oscillator, which is located in cells, tissues or organs outside of the suprachiasmatic nucleus (the site of the master oscillator in mammals).

Additional AO3 Are EP’s and EZ’s as separate as some studies make out or do they interact? How might we evaluate the animal research that has been conducted?

Exam question Discuss the role of endogenous pacemakers in the control of one or more biological rhythms. (Total 16 marks) Discuss research into circadian rhythms. In the your answer refer to research evidence. (Total 16 marks) Discuss and evaluate research into infradian and Ultradian rhythms. (Total 16 marks)