Biological rhythms: circadian rhythms AO1

Question 1

What are biological rhythms?

Answer 1

Biological rhythms are patterns that all living organisms - plants, animals, and people - are subject to, influencing body systems’ behavior.

Question 2

What governs biological rhythms?

Answer 2

Biological rhythms are governed by endogenous pacemakers (internal biological clocks) and exogenous zeitgebers (external environmental changes).

Question 3

What are ultradian rhythms?

Answer 3

Ultradian rhythms are biological rhythms that occur many times during the day.

Question 4

What are infradian rhythms?

Answer 4

Infradian rhythms are biological rhythms that take longer than a day to complete.

Question 5

What are circannual rhythms?

Answer 5

Circannual rhythms are biological rhythms that take much longer than a day to complete.

Question 6

What are circadian rhythms?

Answer 6

Circadian rhythms last for around 24 hours, with ‘circadian’ derived from Latin meaning ‘about a day’.

Question 7

What are two examples of circadian rhythms?

Answer 7

Two examples of circadian rhythms are the sleep/wake cycle and core body temperature.

Question 8

What influences the sleep/wake cycle?

Answer 8

The sleep/wake cycle is influenced by daylight, an important exogenous zeitgeber.

Question 9

What is the role of the suprachiasmatic nucleus (SCN)?

Answer 9

The SCN is an internal pacemaker that governs the sleep/wake cycle and is located just above the optic chiasm.

Question 10

What happens if the biological clock is left without external stimuli?

Answer 10

If left without external stimuli, researchers question whether we would still fall asleep and wake up at regular times.

Question 11

Who is Michel Siffre?

Answer 11

Michel Siffre is a self-styled caveman who studied the effects of being underground on his biological rhythms.

Question 12

What was Siffre’s cave study?

Answer 12

Siffre was deprived of exposure to natural light and sound but had access to adequate food and drink to study his biological rhythms.
- he resurfaced mid september 1962 after two months in the caves of the southern sails believing it to be mid august
- a decade later he performed a similar feat but this time in a texan cave
- in each case his ‘free-running’ biological rhythm settled down to one that was just beyond the usual 24 hours (around 25) though he did continue to fall asleep and wake up on a regular cycle.

Question 13

explain other research into circadian rhythms

Answer 13

• similar results to Strife were recorded by Aschoff and Wever (1976) who convinced a group of participants to spend 4 weeks in a WW2 bunker deprived of natural light.
• all but one of the participant (sleep wake cycle of 29 hours it extended to) displayed a circadian rhythm between 24/25 hours
• suggests that the natural sleep/wake cycle may be slightly longer than 24 hours but it is entrained. y exogenous zeitgebers associated with our 24 hour day.
• despite this we should not overestimate the influence of exogenous zeitgebers on our internal biological clock. Collard et al (1985) studies a group of 12 who agreed to live in a dark cage for three weeks retiring to bed when the clock said 11:45pm and rising when it said 7:45am. Over time the researchers gradually sped up the clock so an apparent 24 hour day actually lasted 22 hours. it was revealed only one of the participants could comfortably adjust to the new regime. Suggests that the existence of a strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers