A01 Biological Rythms: Infradian And Ultradian Rhythms

• The menstrual cycle


  The female menstrual cycle is an example of an infradian rhythm. It is goverened by monthly changes in hormone levels which regulate ovulation.
• Cycles


  Cycle refers to time between first day of woman's period (womb lining is 'shed') to the day before the enxt period. A typical cycle is 28 days to complete but 24-25 days is considered normal.
• Cycle effects on hormones

  During each cycle, increasing levels of the hormone oestrogen cause the ovary to develop an egg and release it (ovulation). After ovulation, the hormone progesterone helps the womb lining grow thicker, readying the body for pregnancy. If pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leavest he body (the mestrual flow)
• Research study


  The menstrual cycle is an endogenous system but it could influence by exogenous factors like the cycles of other women. Stern and McClintock demonstrated how menstrual cycles may synchronise beacuse of the influence of female pheremones.
• Stern and McClintock study

  29 women ppts with history of irregular periods. Samples of pheremones gathered from 9 women at different stages of menstrual cycle via a cotton pad placed in their armpit which was worn for at least 8 hours to ensure the pheremones were picked up.
• Cotton pads


  The pads were treated with alochol and frozen to be rubbed on the upper lip of other ppts. On day one, the pads from the start of the mesntrual cycle applied to all 20 ppts and at day two, all were given a pad from the 2nd day of cycle and so on.
• Stern and McClintock study findings

  It was found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour doner'.
• Seasonal affective disorder (SAD)


  Depressive disorder which has a seasonal pattern of onset, classified as a mental disorder using DSM-5.
• Symptoms of seasonal affective disorder (SAD)

  Persistent low mood alongside a general lack of activity and interest in life. Often referred to as the winter blues as symptoms are triggered during winter months, daylight hours are shorter.
• Rythms of seasonal affective disorder (SAD)

  Has a particular infradian rhythm called a circannual rhythm as it is subject to a yearly cycle. It's also classed as a circadian rhythm as it may be caused by a disruption of sleep/wake cycle.
• Hormonal explanation for seasonal affective disorder (SAD)


  Hormone melatonin is implicated in the cause as during the night the pineal gland secretes melatonin until dawn when there's an increase in light. during the winter months a lack of light means the secretion process continues, its thought to have a knock-on effect on the production of seratonin in the brain which cause the depressive symptoms
• Ultradian rhythms


  Biological rhythms that occur more than once each day. Most researched one are the stages of the sleep.
• Stages of sleep cycle research

  There are five distinctive stages of sleep that span approximately 90 minutes. Each stage is charactersied by different brain-wave activity which can be monitored using EEGs.
• Stages 1 and 2 of sleep cycle

  'Sleep escalation' is light sleep where person can be easily woken. Brain wave patterns start to become slower and more rhythmic (alpha waves) and becoming more slow as the sleep gets deeper (theta waves).
• Stages 3 and 4 of sleep cycle

  Delta waves which are also slower and have a greated amplitude. This is deep sleep or slow wave sleep and this makes it difficult to rouse someone in their sleep.
• Stage 5 of the sleep cycle

  REM sleep where the body is paralysed yet the brain activity speeds up significantly in a manner ressembling an awake brian. This is hihgly correlated to dreaming
• Meaning of REM sleep

  Rapid eye movement. This name is given as REM sleep denotes fast activity of the eye under the eyelids.