psychology

CIRCADIAN RHYTHMS - (sleep wake cycle) A circadian rhythm repeats in a cycle of once every 24 hours.The 24-hour sleep–waking cycle is a good example of a circadian rhythm because it clearly shows that the circadian rhythms depend on an interaction of physiological and psychological processes. Our fairly consistent sleep pattern suggests an internal or endogenous mechanism the biological clock. An example of which is siffre's study where he spend 2 months in a dark cave and his sleep wake cycle changed to 25 hours which is close to the carcadian sleep wake cycle of 24 hours.

INFRADIAN RHYTHMS - (menstrual cycle) An infradian rhythm involves a cycle greater than 24 hours. For example, the human menstrual cycle occurs every 28 days, although it can be 20–60 days. It is controlled by the hormones oestrogen and progesterone The hormones cause the release of the egg and thickening of the lining of the womb so that it is ready to receive a fertilised egg. If the egg is not fertilised the lining is shed and so menstruation is the outcome of a cycle of activity that prepares the body for conception. Menstruation is an endogenous mechanism as it is controlled mainly by internal biological factors (the hormones) but exogenous factors (external cues) can also affect the rhythm.