infradian rhythms

• what is an infradian rhythm?

  a cycle that has a duration of over 24 hrs, and may be weekly, monthly or even annually
• give examples of weekly rhythms

  • testosterone levels in men elevated at weekends
  • more sexual activity at weekends
  • frequency of births is lower during weekends
• give an example of a monthly rhythm

  menstrual cycle
• how long does a menstrual cycle last?

  1 month
• what is the average length of a menstrual cycle

  28 days
• what role do hormones play in the menstrual cycle?

  • endogenous system that governs the menstrual cycle
  • promote ovulation or stimulate the uterus for fertilisation
  • ovulation occurs halfway through the menstrual cycle when oestrogen levels peak, and lasts 16-32 hrs
  • after ovulation, progesterone levels increase in preparation for a possible embryo implantation in the uterus
  • if no pregnancy, progesterone levels fall and uterus lining sheds
• what can the endogenous rhythm of the mesntrual cycle be controlled by?

  • exogenous cues
  • eg- light and pheromones
  • pheromones are chemical substances produced by the body and secreted into the air. These are absorbed into the blood stream and act like hormones
  • causes women who live or work closely near each other to have synchronised menstrual cycles
• state examples of annual infradian rhythms in mammals

  • migration in response to temperature change
  • seasonal variation mood in humans- more depressed during winter (seasonal effect disorder), especially in women (Magnusson)
• AO3 for infradian rhythms?

  • 😊 exogenous control- light, Reinberg et al- woman spent three months in cave with little light. MC shortened (sleep wake cycle lengthened) took one yr to be normal again (unethical),
  • 😊support for pheromones- Russel- samples of sweat taken daily from group of women and rubbed onto upper lip of another group. Groups kept separate yet cycles synchronised
  • 😊synchronisation adaptive- McClintock et al- women who work with men have shorter menstrual cycles- male hormones can reset woman's bio clock
  • 😊determinist- pre-menstrual syn controls behavior (can explain crime + suicide)- can help us to understand mood swings as a result of hormonal changes in women. However, it negates the role of free will