Biological Rhythms and Sleep
What is a biological rhythm?
• Cyclical changes in the way biological systems behave.
• Most obvious rhythm is the sleep-wake cycle – people and many animals go to sleep when it is dark and wake up when it is light.
• There are other many other rhythms, e.g. the opening and closing of flowers with daylight, seasonal patterns of activity in hibernating animals.
What controls these rhythms?
• Internal biological ‘clocks’, called endogenous pacemakers.
• External cues from the environment, called exogenous zeitgebers. These include sunlight, food, noise, or social interaction.
3 main types of rhythm
• Circadian rhythms – cycles lasting approx 24 hours e.g. Sleep/waking cycle, body temperature cycle, metabolic rate cycle
• Ultradian rhythms – cycles shorter than 24 hours (or more than 1 cycle per 24 hours) e.g. Sleep cycles, hormone release, foraging
• Infradian rhythms – cycles lasting longer than 24 hours e.g. menstrual cycle
• These are rhythms lasting ‘about one day’.
• E.G. sleep-wake cycle, body temperature, urine production. Some…