Biological Rhythms 2: Infradian Describe and evaluate research into infradian rhythms Give examples of Infradian Rhythms

Infradian rhythms Cycles that have a period greater than 24hrs, but less than a year e.g: Menstrual cycle – females Male monthly cycle! – body temperature and mood/alertness Seasonal Affective Disorder (SAD) – also known as a circannual rhythm

Infradian rhythms-Endogenous Control  Monthly cycles...the function of this cycle is to regulate ovulation. The menstrual cycle is controlled mainly by the hormones oestrogen and progesterone. On average this cycle takes 28 days but varies slightly between individuals

The Menstrual Cycle ovulation LH FSH Hormone Levels

The Menstrual Cycle: Endogeous or Exogenous? The menstrual cycle is governed by an endogeous system-the release of hormones under the control of the pituitary gland. However it can be controlled by exogenous cues.

External control (zeitgebers) Russell et al (1980) collected a sample of sweat from one group of women and rubbed it onto the upper lip of women in the second group. Their menstrual cycles became synchronised. This suggests that the menstrual cycles are affected by pheromones. Evolutionary advantages of external control of the menstrual cycle. Bentley (2000) believed that synchronisation between women living in close proximity would ensure that the women would conceive and give birth at similar times.

Consequences of the menstrual cycle: PMS This is a collection of symptoms that usually occurs four or five days before menstruation. Symptoms include irritation, depression, headaches and a decline in alertness. Other possible symptoms, according to Luce (1971) include insomnia, cravings for certain foods.

PMS Dalton (1964) reported a sharp increase in crimes, suicides, accidents and a decline in schoolwork associated with PMS. However, Keye (1983) concluded that although a small minority of women may suffer in this way, such extreme symptoms are relatively rare. A.I.Ds Determinist approach (certain behaviours are inevitable, we have no choice!) PMS appears to have an underlying physiological cause, as evidenced by the fact that it is reported in all cultures. Has been used as legal defence!

Biological Rhythms 2: Infradian Describe and evaluate research into infradian rhythms Give examples of Infradian Rhythms: The Menstrual cycle, SAD

SAD Some infradian rhythms occur on a seasonal basis and are known as circannual rhythms (e.g. migration in birds, hibernation) SAD is Linked to the lack of light. Sufferers’ symptoms are more severe than the normal lowering of mood when daylight hours are shorter. More darkness means more melatonin, and more melatonin means less serotonin. Low levels of serotonin are associated with depression.

Analysing research into Infradian Rhythms Real world applications Research into SAD has led to effective treatments suggesting that the theory has some validity. However, there does also appear to be a genetic component. Describe what phototherapy is and how it can be used to treat SAD.

Research Activity : Compare the human infradian rhythm with one of a chosen animal (you will need to research this) For both include detail of the internal endogenous controlling pacemakers and the external exogenous zeitgebers they are sensitive to. Prepare a short presentation for the class. Names will go into a hat to choose 3 people to give their presentations to the class next lesson

Biological Rhythms 2: Infradian Describe and evaluate research into infradian rhythms Give examples of Infradian Rhythms: The Menstrual cycle, SAD