Rhythms

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

Circadian Rhythms

•          These are rhythms lasting ‘about one day’.

•          E.G. sleep-wake cycle, body temperature, urine production. Some…