Biological Rhythms and Sleep

  • Circadian
  • Infradian
  • Ultraduan
  • endogenous pace makers and exogenenous zeigebers
  • What happens if you dissrupt these
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  • Created by: Annabelle
  • Created on: 13-01-11 18:07

Bio Rhythms

  •   The term refers to regular variations in biological activity. It includes changes in levels of brain chemicals, increases and decreases in body temperature and the shift between sleeping and waking  
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Types of rhythm


Because of the variety of rhythms they need to be put in different types such as: Circadian Infradian Ultradian  

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What controls these rhythms?

Light – we go to sleep when dark and wake up when it is light

Food scarcity – birds migrate and squirrels hibernate when food is scarce

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Exogenous Zietgeber

This suggests that biological rhythms are controlled by environmental factors such as:



Availability of food

These are called exogenous zietgebers (German for external time givers)

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However, many studies have shown that it is not that simple.

If beach living algae are kept in a laboratory in controlled conditions they still burrow into the sand and come out at times in time with the tides.


Squirrels kept in controlled conditions still prepare for hibernation as winter approaches in the world outside by putting on weight and decreasing body temperature.

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So there must be some sort of internal clock that regulates rhythms when there are no zeitgebers.

These internal clocks are called endogenous pacemakers

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This word comes from the Latin for ‘about a day’.

The sleeping waking cycle involves one period of each in 24 hours

Our body temperature has one peak (in the afternoon) and one trough (in the early morning) in the same period

This is a 24 hour rhythm

What are four things which have some variation over 24 hours?


1. heart rate

2. breathing

3. metabolic

4. body temperature

All the above reach maximum values in late pm/early evening and minimum values in the early hours of the morning



We are active during the day and inactive at night

These rhythms persist if we suddenly reverse our activity patterns.

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These also vary in concentration over the day.


Why would this happen?

This is so energy is provided when needed so for example is makes sense for the body temperature to dip in the middle of the night when we are inactive i.e. asleep

The rising body temperature in the day allows for increased activity and energy expenditure

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Approaches, Issues and Debates

Approaches, Issues and Debates

Which of these link to this topic so far?


Approach – biological

Debate – reductionist

Issues – use of animals coming up

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Menstruation #

These have a rhythm of more than a day.

What do you think has been most researched under this?


Menstrual cycle


Every 28 days female bodies have several changes with two possible outcomes

What are they?





The menstrual period is the end of the cycle not the beginning.  The womb has prepared to house and nourish a fertilized egg

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Pre menstrual syndrome – PMS

Five days before a period women may have:

Mild depression


Decrease in alertness


A day of energy followed by lethargy

AO2 #

PMS occurs in all cultures which indicates a physiological cycle rather than a pattern of behaviour because of the culture

Primates also suffer similar effects AO2

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In lighter months of the year conception increases so light levels may have an influence on the pituitary gland – this gland controls the menstrual cycle


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Seasonal Affective Disorder is a form of depression that affects certain people in the winter months.

These people tend to eat and sleep more.

If sufferers are exposed to bright light first thing in the morning this can help combat SAD

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Ultradian Rhythms #

These are rhythms of less than a day’s length. i.e. sleep

During the night we move into different stages of sleep - light slow wave sleep to deep slow wave sleep. And into REM

One cycle takes about 90 minutes


This cycle is controlled in the brain using neurotransmitters.

The key elements are suprachiasmatic nucleus (SCN) and the pineal gland

Other examples

There are other examples of ultradian rhythms.

Some studies of alertness in humans show that it can vary within 90 minute periods


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