biological rhythms

• What is a biological rhythm?

  Cyclical patterns within biological systems that have evolved in response to environmental influences, e.g. day and night
• What are two key factors that govern biological rhythms?

  Endogenous pacemakers and exogenous zeitgebers
• What are endogenous pacemakers?

  Internal factors, the body's biological clocks
• What are exogenous zeitgebers?

  External factors, changes in the environment
• What is a circadian rhythm?

  A 24 hour rhythm
• Where does the word circadian come from?

  The Latin 'circa' which means 'about', and 'dian', which means 'day
• What are two examples of circadian rhythms?

  Sleep-wake cycle and body temperature
• What does the sleep-wake cycle do?

  Dictates when humans and animals should be asleep and awake
• What is the external zeitgeber for the sleep-wake cycle?

  Light
• Once light is detected by the eye, what happens?

  Sends messages concerning the level of brightness to the suprachiasmatic nuclei (SCN)
• What does the suprachiasmatic nuclei do?

  Uses the information about light to coordinate the activity of the entire circadian system
• What else determines the sleep-wake cycle?

  Homeostasis
• How is homeostasis involved in the sleep-wake cycle?

  When an individual has been awake for a long time, homeostasis tells the body that there is a need for sleep because of energy consumption
• How does the homeostatic drive for sleep change during the day?

  Increases throughout the day, reaching its maximum in the late evening, when most people fall asleep
• How does the human body temperature change throughout the day?

  At its lowest in the early hours of the morning (36ºC at 4:30 am) and at its highest in the early evening (38ºC at 6 pm).
• How does the human body temperature interact with the sleep-wake cycle?

  Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning
• What is an infradian rhythm?

  A cycle longer than 24 hours
• What are two examples of infradian rhythms?

  Menstrual cycle and SAD
• What is SAD?


  Seasonal Affective Disorder is a type of winter depression which affects millions of people every winter between September and April, in particular during December, January and February
• SAD is also known as a what kind of rhythm?

  Circannual rhythm, as it is subject to a yearly cycle
• What is SAD caused by?

  A biochemical imbalance, this is thought to be melatonin, in the hypothalamus due to the shortening of daylight hours and the lack of sunlight in winter
• How does SAD vary between individuals?

  For many people SAD is a seriously disabling illness, preventing them from functioning normally without continuous medical treatment. For others, it is a milder condition
• When does SAD usually begin for individuals?

  SAD may begin at any age, but the main age of onset is 18-30
• In what areas of the world does SAD occur?

  It occurs throughout the northern and southern hemispheres but is rare in those living within 30 degrees of the Equator, where daylight hours are long, constant and extremely bright
• What is menstruation characterised by?

  By a change in hormone levels which regulate ovulation
• How long is the typical menstrual cycle?

  28 days
• What happens throughout the menstrual cycle?

  Rising levels of oestrogen cause the ovary to develop an egg and release it (ovulation). After ovulation progesterone helps the womb grow thicker, preparing for pregnancy. If pregnancy doesn't occur then the egg is absorbed and the womb lining comes away
• What is an ultradian rhythm?

  Last less than 24 hours
• What is an example of an ultradian rhythm?

  Stages of sleep
• What does the sleep cycle alternate between?

  REM (rapid eye movement) and NREM (non-rapid movement) slee
• How many stages of sleep are there?

  5
• On average, the cycle repeats over what amount of time?

  90 minutes
• What are stages 1 and 2?

  'light sleep' stages
• What are brainwaves like during stages 1 and 2?

  Become slower and more rhythmic, starting with alpha waves progress to theta waves
• What are stages 3 and 4?

  'deep sleep' or slow wave sleep stages, where it is difficult to wake someone up
• What are brainwaves like during stages 3 and 4?

  This stage is associated with slower delta waves
• What is stage 5?

  REM (or dream) sleep. Here is the body is paralysed (to stop the person acting out their dream)
• What are brainwaves like during stage 5?


  Brain activity resembles that of an awake person