Biological rhythms

• Biological rhythms


  A biological rhythm is a change in body processes or behaviour in response to cyclical changes inside and outside the body.
• circadian rhythms


  Circadian rhythms are biological rhythms that last 24 hours i.e. a day. This means that there is one cycle every 24 hours. An example is the sleep/wake cycle which has one sleep period (typically 8 hours) and one waking period (typically 16 hours) every 24 hours. The circadian sleep wake cycle is regulated by endogenous pacemakers and exogenous zeitgebers.
• Describe Endogenous pacemakers


  Internal body clocks that play a main role in controlling biological rhythms.

  e.g. Suprachiasmatic nucelus (SCN), pineal gland, and melatonin
• Describe Exogenous zeitgebers


  Environmental factors that synchronise biological rhythms with the outside world.

  e.g. Light and social cues e.g. meal patterns
• Describe the role of endogenous pacemakers and exogenous zeitgebers on the sleep/ wake cycle

  Night-Time: - No light perceived by the retina. - SCN instructs the pineal gland to secrete melatonin. - Melatonin induces tiredness, helping us fall asleep. Day-Time: - Light perceived by the retina. - SCN stops the pineal gland from secreting melatonin. - Inhibited melatonin production keeps us awake.
• Evaluate the role of endogenous pacemakers and exogenous zeitgebers on the sleep/wake cycle

  ✅️ For endo: there is research to support: Ralph (1990)

  ✅️ For exo: there is research to support : blind people

  ❌️ as seperate factors influencing the sleep/wake cycle is that

  ✅️ where endogenous pacemakers and exogenous zeitgebers work together, is more accurate than focusing on one factor in isolation.
• ultradian rhythms


  Ultradian rhythms are biological rhythms that last less than 24 hours. This means that there is more than one cycle every 24 hours. Sleep stages are an example of an ultradian rhythm. This is because each cycle lasts approximately 90-100 minutes and consists of 5 stages that repeat throughout the night approximately 4-5 times in a rhythmic pattern:
• stage 1 and 2: ultradian rhythms

  Light sleep:

  Alpha & theta waves

  heartrate slows and body temp drops
• stage 3 and 4 of Ultradian rhythms

  Deep sleep:

  Delta waves

  Metabolic rateslows, growth hormone is produced
• stage s of Ultradian rhythms

  Rapid eye Movemen [REM] sleep :

  Beta waves

  Brain activity is similar to that of an awake brain. Dreaming occurs
• Describe the menstral cycle as an infradian rhythm

  The infradian menstrual cycle is controlled by the pituitary gland, which releases hormones around day 14 to increase oestrogen, triggering ovulation. Progesterone then thickens the womb lining for pregnancy, and if pregnancy doesn’t occur, the lining is shed during menstruation.
• What did Russel descover about the female menstrual cycle

  Russell et al. (1980) Study: Investigated menstrual cycle synchronization. - Method: Sweat samples from one group of women were applied to the upper lip of another group. - Findings: Women’s menstrual cycles synchronized despite being kept apart. Synchronization was influenced by pheromones, an exogenous zeitgeber. -Conclusion: Infradian rhythms, like the menstrual cycle, can be affected by external factors.