AO1

• An ultradian rhythm is one that has a duration shorter than 24hrs
• An example of an ultradian rhythm is the sleep cycle
• An infradian rhythm is a rhythm that has a duration longer than 24hrs
• An example of an infradian rhythm is the mensmenstrual cycle
• The human female menstrual cycle with a periodicity on average of 28 days. The menstrual cycle is regulated by hormones which either promote ovulation or stimulate the uterus for fertilisation. Ovulation

  occurs roughly halfway through the mensural cycle when oestrogen levels peak and usually last for 16-32 hours.
• It would appear that the menstrual cycle is governed by endogenous systems with the release of hormones by the pituitary gland. However it can also be controlled by exogenous zeitgebers cues
• Another example of an Infradian rhythm is SAD here sufferers can experience serve depression during the winter months . This has led to phototherapy being used to suppress melatonin, to stop extreme fatigue and promote wakefulness.
• RESEARCH EVIDENCE INTO SAD:

  • Blakemore reported the case of Pat Moore who had a history of suffering from unipolar depression before she realized that her depression was seasonal. The effect of day light on her mood was tested through exposure to light therapy (phototherapy) for a few hours on waking. The bright white light used was as similar as possible to natural light. Pat showed remarkable improvement within just a few days of beginning therapy.
• The sleep cycle, the basic rest activity cycle and the pattern of human meals
• The alternation between NREM and REM sleep in sleep. Wakefulness and sleep is an example of a circadian rhythm however within the sleep portion of this cycle an ultradian rhythm exists. The cycle happens every 90 minutes, follows a pattern of 4 stages of NREM sleep and stage 5 REM sleep.
• Stage 5 is commonly referred to as REM sleep

  • This makes up between 20-25% of our total sleep pattern. It is characterised by Rapid eye movements and the speed of brainwaves increases and dreaming occurs.