I have been struggling with question 40 on page 9.20 where it asks:

** The circadian rythm of body temperature which influences the natural sleep cycle is???

The ENTIRE circadian rythm is a 25 hour cycle but the 'temperature' cycle is a 12 hour cycle between 6pm and 6am. The sleep cycle is part of the overall cycle but the temp cycle is only 12 hours - refer graph on page 9.10

Please tell me what I am missing - your answer to the question is (b) and mine is (d).

Anyway, doing this exam on Thursday - the last one in the series so I'll let you know how I go. It has been a lot of fun.

Hi Brenton,

The temperature rhythm actually favours a 25 hour cycle (not 12) and if you left someone in isolation and allowed them to sleep whenever they felt they needed it, the circadian rhythms and the sleep/wake cycles would sync at about a 25 hour day.

Now, in real life, the cycles are more like the 24 hour cycle we are used to because there are a lot of external cues that also influence us and our body rhythms. The body therefore tries to shorten its rhythms to match the regular 24 hour cycle.

Remember a "cycle" in a circadian rhythm is not from a peak to a tough but rather from peak to peak. So, in the example you mentioned the cycle goes from 6pm to 6pm and not 6pm to 6am. Remember, in the absence of external influences it would actually go from 6pm to 7pm the next day (25 hours).

Option D can't be correct because the circadian rhythms don't run with a 12 hour cycle but rather 25 hours. B is correct because research has shown that, left to its own devices, a body will tend to sync on this 25 hour cycle with the subject feeling the need for sleep an hour later each day.

Cheers,

Rich

P.S. good luck with your exam!