Biological Rhythms- Circadian, Infradian, Ultradian

What is meant by biological rhythms? AO1

distinct patterns of changes in body activity that conform to cyclical time periods

What are biological rhythms influenced by? AO1

1. Endogenous Pacemakers

2. Exogenous Zeitgeber

What is an endogenous pacemaker? AO1

-give an example

internal body clock

example= SCN (superchiasmatic nuclei)

What is an exogenous zeitgeber? AO1

-give examples

external changes in the environment

examples= light, social cues

What are different biological rhythms? AO1

1. Circadian rhythms

2. Infradian rhythms

3. Ultradian rhythms

What is a circadian rhythm? AO1

-what is an example of a circadian rhythm?

a type of biological rhythms that is subject to a 24 hour cycle

example= sleep-wake cycle, core body temp

What is the sleep-wake cycle? AO1

it is an example of a circadian rhythms and dictates when humans and animals should be asleep and awake

Outline the sleep-wake cycle? AO1

1. Light provides the primary input to this system acting as the external cue (exogenous zeitgeber) for sleeping and waking

2. Light is first detected by the eye and sends messages concerning the levels of brightness to the superchiasmatic nuclei (SCN)

3. SCN is the endogenous pacemaker

What happens if the SCN detects little light? AO1

when little light is detected by the SCN the pineal gland is activated and releases melatonin, this induces sleep

What is one study that investigated circadian rhythms? AO1

Siffre’s Cave Study

What did Siffre do? AO1

He spent extended periods of time underground in a cave deprived from light and sound

What did Siffre find?

What did Siffre conclude? AO1

Siffre’s biological rhythm extended to 25 hours

concluded=body’s internal clock is set at 24-25 hours in the absence of external cues

What is one strength of circadian rhythms? AO3

+ve: Supported by Research

For example, Siffre conducted a case study where he spent an extended period of time underground in a cave deprived of light and sounds (exogenous zeitgebers)

He found that his biological rhythms extended to a maximum of 25 hours in the absence of external cues

This suggests that our circadian rhythm does operate in the absence of external cues and it has a natural cycle of 24-25 hours

Therefore strengthening the presence of circadian rhythms

What is one weakness of Siffre’s research into circadian rhythms? AO3

-ve: Siffre’s evidence is from a Case Study

This is a weakness because it only focuses on the one individual (Siffre) and the effects exogenous zeitgebers had on his own internal body clock

Given that Siffre only studied himself it is very difficult to generalise his findings to whole populations of people

It needs to be considered that individual differences could possibly make individuals respond differently

Therefore Siffre’s evidence lacks population validity

What is one strength of circadian rhythms? AO3

+ve: Practical Application

This is because research into circadian rhythms has increased our understanding of the consequences that may occur if they are disrupted

For example, research has shown that night shift workers suffer a concentration lapse at 6am increasing the likelihood of accidents, as well shift workers are three times more likely to suffer from heart disease as a result of the stress of adjusting to a new sleep-wake cycle

This shows that there may be economic, social and health implications, such as maintaining worker productivity and preventing accidents in the workplace, when a circadian rhythm is desynchronised

Therefore strengthening the importance of maintaining a synchronised circadian rhythms

What is an ultradian rhythm? AO1

-what is an example of an ultradian rhythm?

a type of biological rhythm that is subject to a period shorter than 24 hours

example= sleep cycle

What is the sleep cycle? AO1

This cycle alternates between REM and NREM sleep and consists of five stages.

On average, the entire cycle repeats every 90 minutes so a person can experience 4-5 cycles in a night

What is used to study the sleep process? AO1

EEG records as they highlight the distinct brain wave patterns throughout the night during the different stages of sleep

What are stages 1 and 2? AO1

-what type of wave?

Stages 1 and 2 are ‘light sleep’ stages

Brainwave patterns become slower and more rhythmic, starting with alpha waves and they progress to theta waves

What are stages 3 and 4? AO1

-what type of wave?

Stages 3 and 4 are ‘deep sleep’ or slow wave sleep stages, and is where repair is undertaken

Associated with slower delta waves

What is stage 5? AO1

-what type of wave?

Stage 5 is REM sleep (dream sleep)

Here the body is paralysed and brain activity resembles that of an awake person

What is one strength of ultradian rhythms? AO3

+ve: Supported by Research

For example, Dement and Kleitman studied the sleep patterns of 9 ppts in a sleep lab. Brainwave activity was recorded on an EEG throughout the night. Ppts were woken up during the night and asked to report if they were having a dream

They found that sleep is an active state that is made up of different identifiable stages, and that the average time in one cycle was 90 minutes

This demonstrates that the sleep cycle is an example of an ultradian rhythm, given that around 4-5 cycles are experienced each night

Therefore strengthens the validity that our sleep cycle is an example of an ultradian rhythm

What is one weakness of ultradian rhythms? AO3

-weakness of Dement and Kleitman’s research?

-ve: Conducted in a Controlled Lab Setting, so can be criticised for its Artificial Nature

This is because the ppts slept under circumstances that don’t usually reflect their ‘typical’ nights sleep, given that they had electrodes attached to their body/head and were often woken up a numbers of times throughout the night in order to report dreams

These conditions are very unlikely to bear much relation to the ppts normal sleep environment at home and are likely to have in fact disrupted their sleep

Thus reducing the ecological validity of the research

What is one weakness of ultradian rhythms? AO3

-weakness of Dement and Kleitman’s research?

-ve: Consisted of a Small Sample

For example they only studied 9 ppts sleep all of whom slept in an artificial environment anyway

Given that limited results were obtained it is very difficult to generalise the findings from their research to a whole population

Therefore reducing the population validity of the research

What is an infradian rhythm? AO1

-what is an example of an infradian rhythm?

a type of biological rhythm that is subject to a period longer than 24 hours

could be weekly, monthly or annually

example: monthly infradian rhythm= female menstrual cycle

What is the female menstrual cycle? AO1

it is an example of a monthly infradian rhythm and is regulated by hormones that either promote ovulation or stimulate uterus for fertilisation

How long does the average menstrual cycle last? AO1

cycle is around 28 days

although there is variation with some women experiencing a short cycle of 23 days and other experiencing longer cycles of up to 36 days

What is meant by ovulation? AO1

-when does it occur?

=rising levels of hormone oestrogen cause ovary to develop an egg and release it

occurs halfway through the cycle

What is the release of oestrogen? AO1

endogenous pacemaker (internal)

What happens after the ovulatory phase? AO1

progesterone levels increase in preparation for the possible implantation of an embryo in the uterus

What factors can also influence the menstrual cycle? AO1

-what are these called?

-Stress

-Diet =exogenous zeitgebers

-Medication

What is one strength of infradian rhythms? AO3

+ve: Supported by Research

For example, McClintock studied 29 women with a history of irregular periods. She obtained samples of pheromones from 9 of the women at different stages in their cycle via cotton pads under their armpits. The pads were treated with alcohol and then wiped under the noses of the other 20 women. She found that 68% of women experienced changes to their cycle.

This demonstrates that exogenous zeitgebers (pheromones) have directly affected our endogenous pacemaker (ovulation)

Thus strengthening the presence of infradain rhythms

What is one weakness of infradian rhythms? AO3

-weakness of McClintocks research?

-ve: Methodological Issues

The first is that there are many different factors that could affect a woman’s menstrual cycle and act as confounding variables, including stress and diet- this reduces the internal validity of the results

Another issue is that the research used a small sample of women so it is difficult to generalise the findings to a whole population. Individual differences such as their age, also need to be considered.

Also research relied on a self-report method- possible that the ppts provided invalid answers as they were embarrassed or felt uncomfortable sharing with the researcher

Therefore reducing the validity of the research