biological rhythms: Circadian rhythms

Biological rhythms

All living organisms are subjected biological rhythms and these exert an important influence on the way in which body systems behave. Biological rhythms are distinct patterns of changes in body activity that conform to cyclical time periods, they are governed by two things : the bodies internal biological clocks which are called and endogenous pacemakers and external changes in the environment known as exogenous zetigebers

Some of these rhythms occur many times during the day (ultradian rhythms) and others take longer than a day to complete (Infradian rhythms)

Circadian rhythms are rhythms that last for around 24 hours, two examples are: the sleep/wake cycle and core body temperature

The sleep/wake cycle

The sleep week cycle is covered by exogenous zetigebers like daylight which has an effect on feeling active during day and tired during night but also endogenous pacemakers which is a biological clock called the Superchiasmatic nucleus (SCN). The SCN lies just above the optic chiasm which provides information from the eye about light. Exogenous zetigebers (light) can reset the SCN

Siffre’s case study

• Micheal Siffre is a self-styled caveman who has spent several extended periods under the ground to study his own biological rhythms

• He was deprived of exposure to natural sunlight and had access to food and drink - he spent two months in the cave

• A decade later he performed a similar study for six months

• He found that he fell asleep and woke up on a regular schedule

Other research

• similar results were recorded by Ashoff and Weber (1976) who convinced a group of participants to spend four weeks in WW2 bunker deprived of natural light. But one participant (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25

• Simon Folkard (1985) studied a group of 12 people who agreed to live in a dark cave for 3 weeks, retiring to bed when the clock said 11:45 pm and rising when it said 7:45 am. over the course of the study the researchers gradually speeded up the clock so 24 day only lasted 22 hours

Strengths

• One strength of circadian rhythms is that it has been used to improve medical treatments - circadian rhythms coordinate a number of the bodies’ basic processes such as a heart rate, digestion and hormone levels. These fries and fold during the day which has led to the field of chronotherapeutics (how medical treatment can be administered in a way that corresponds to a persons biological rhythms). For example, aspirin as a treatment for heart attacks is most effective if taken last thing at night.

• Another strength is that it provides an understanding for the consequences that occur if it is disrupted - for example night workers engaged in a shift work experience period of reduced con around six in the morning, meaning mistakes and accidents are more likely according to Bolivian (1996). This shows that research into the sleep/wake cycle may have real world economic implication in terms of work productivity.

Limitation

• One limitation of circadian rhythms is that generalisations are difficult to make - studies such as Aschoff and Wever and Siffre all based on very small samples of participants. It seems that sleep/wake cycles can vary from person to person. Research from. Charles Czeisler (1999) found individual differences in sleep/wake cycles varying from 13 to 65 hours. In addition a study by Duffy (2001) revealed that some people have a natural preference for going to bed and waking up early (known as larks) whereas some prefer the opposite ( known as owls)