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Circadian Rhythms: Keeping Time

The rotation of the Earth around the Sun, and the Moon around the Earth, produce the cycles that we know as night and day, lunar months, and years. Animals and plants have rhythms that match these cycles. A simple example of this is activity linked to day and night. Kiwi are active at night; behaviour that is described as nocturnal. Pūkeko are active during the day; behaviour that is described as diurnal. Daily rhythms such as these are called circadian rhythms.

Circadian rhythms are found in most living things, including plants, animals and many microorganisms. These rhythms are the repeating patterns that we see in the biochemical, physiological, and behavioural processes. The rhythms follow a roughly 24-hour cycle linked to the patterns of light and dark in the environment around the organism. Humans are no exception, with processes and behaviours such as sleep, cell division, and alertness following this 24-hour cycle. A fascinating fact about circadian rhythms is that when we take away the environmental cues such as light and dark, or the temperature changes that occur during the day and night, the rhythms keep going. If you place a person in a room where there is always light and the temperature never changes, they will still follow a roughly 24-hour pattern of sleeping and waking. This led scientists to suspect that the rhythm is controlled by a biological clock inside the organism.

Dr Guy Warman is a Senior Lecturer in Anaesthesiology at the University of Auckland. Guy leads a team of researchers from the Faculty of Medical and Health Sciences and the School of Biological Sciences, working on understanding human biological clocks, in particular sleep timing and circadian rhythms, and the similarities between sleep and anaesthesia. The team works on both understanding the fundamental biology of circadian rhythms, and applied research in humans.

Seminar paper
"Circadian Rhythms: Keeping Time" seminar (2.1 MB, PDF)
Pre-seminar paper
"Circadian Rhythms: Keeping Time" pre-seminar paper (887.9 kB, PDF)
Seminar challenge questions
"Circadian Rhythms: Keeping Time" challenge questions (634.8 kB, PDF)
Seminar Power Point slides
"Circadian Rhythms: Keeping Time" Power Point (4.8 MB, PDF)