Biological Rhythms

Question 1

What is a biological rhythm?

Answer 1

Any change in physiological activity that repeats periodically in a set cyclical pattern

Question 2

What is a circadian rhythm?

Answer 2

A cycle that takes approximately 24 hours. Examples include the sleep wake cycle, body temperature, metabolic activity and hormones.

Question 3

What is an infradian rhythm?

Answer 3

One cycle takes longer than 24 hours. Examples include menstruation, hibernation and SAD

Question 4

What is an ultradian rhythm?

Answer 4

One cycle takes less than 24 hours. Examples include feeding, stages of sleep and alertness.

Question 5

How does the menstruation cycle work as an infradian rhythm?

Answer 5

The follicular phase - 10 - 14 days. Low levels of oestrogen and progesterone during menstruation. When the bleeding stops the endometrium grows and thickens. FSH levels rise. This signals ovaries to produce oestrogen which stimulates LH levels to rise. Eggs is released into one of fallopian tubes. LH causes progesterone after ovulation which stimulates the endometrium to prepare a thick blanket of blood vessels to support a fertilised egg.

Question 6

What is body temperature as a circadian rhythm?

Answer 6

Human body temperature is at its lowest in the early hours of the morning and at its highest during early evening. Sleep typically occurs when core temperature starts to drop and body temperature starts to rise towards the end of the sleep cycle, promoting feelings of alertness influenced by muscular activity, digestion and heat loss.

Question 7

What is an endogenous pacemaker?

Answer 7

Internal mechanisms that influence the patterns of our biological rhythms. These may be genetic mechanisms. They help maintain regular rhythms in absence of zeitgebers but they are not perfect and need zeitgebers to synchronise the rhythms to our original behaviours.

Question 8

What is the role of endogenous pacemakers in controlling the sleep wake cycle?

Answer 8

Internal body clock inside the hypothalamus is called the SCN. The SCN receives light through the eyes. When light levels drop, this information is received by the SCN causing it to fire impulses to the pineal gland which secretes melatonin which causes sleepiness. When light increases, melatonin levels fall making us more alert. Without light as a zeitgeber, the process free runs into a 25 hour cycle.

Question 9

Case study to support the role of endogenous peacemakers?

Answer 9

Siffre spent six months in an underground cave. He found that his body was able to free run to a regular pattern of 25 - 30 hours. The internal body clock regulated even without external cues.

Question 10

Problem with using case studies to evaluate endogenous pacemakers?

Answer 10

Siffre was a one off study so results may not be representative. Individual differences make it difficult to generalise findings.

Question 11

Scientific evidence to support the role of endogenous pacemakers?

Answer 11

Ralph took the SNC from a mutant hamster who had a circadian rhythm which mutated to 20 hours. Mutant SNC was transplanted into brains of normal adult hamsters. The normal hamsters took on the circadian rhythm of the mutant hamsters.

Question 12

Is the use of animal studies problematic when evaluating endogenous pacemakers?

Answer 12

Results cannot be extrapolated to explain human brains as many animals are nocturnal. Humans are more adaptable than animals.

Question 13

What are exogenous zeitgebers?

Answer 13

External stimuli/environmental cues that are responsible for resetting the biological clock which provide information about elapsed time and prompt changes in bodily activity and the patterns of our biological rhythms.

Question 14

Is there evidence to support the role of exogenous zeitgebers?

Answer 14

Vetter changed light in the workplace. 4000 kelvin was natural warm light and 8000 kelvin was blue enriched light. Results suggest that blue enriched light and natural light complete as a zeitgeber. Pts working under warmer light tended to synchronise to natural dawn whereas pts exposed to blue enriched light synchronised to office hours.

Question 15

Problem with using artificial tasks as evidence for exogenous zeitgebers?

Answer 15

Vetter’s study used a task with artificial light which could affect the way that the body clock would naturally work so study lacks ecological validity

Question 16

Is there contradictory evidence of light as an exogenous zeitgeber?

Answer 16

Luce and Segal study arctic circle. People still maintain a reasonable constant sleep pattern averaging 7 hours a night despite 6 months of light and 6 months of dark. Appears that social factors reset endogenous rhythms.

Question 17

Do individual differences need to be taken into account when exploring the role of exogenous zeitgebers?

Answer 17

Some people are more alert early in the day and others later. This could be due to lifestyle or age, or the speed at which they adapt to disruptions. Look more holistically.

Question 18

What is jet lag?

Answer 18

The effects we experience when crossing into a different time zone. Estimated that SCN takes several cycles to entrain to a new environment. Winter estimated that it takes 1 day to adjust to each hour of time change. Symptoms include fatigue, insomnia, anxiety, constipation or diarrhoea.

Question 19

What is phase delay?

Answer 19

Travelling from east to west extends your day

Question 20

What is phase advance?

Answer 20

Travelling from west to east shortens your day

Question 21

Is it easier to adjust to phase delay or phase advance?

Answer 21

Phase delay because it is lengthening our day. Our internal rhythm is greater than 24 hours. Phase delay therefore brings external factors closer in line with internal whereas phase advance moves them further away.

Question 22

What is shift lag?

Answer 22

Shift lag is caused by rotating shift. Working at night requires you to be alert at times when you are used to being asleep and vice versa. This means that natural rhythms will be out of synchronisation with most of the available cues from external zeitgebers. Symptoms include fatigue, sleep disturbance, digestive problems, lack of concentration, memory loss and mood swings.

Question 23

What are the effects of shift work?

Answer 23

Knutsson found that individuals who worked shifts for 15yrs were three times more likely to develop heart disease. One main effect is difficulty sleeping during the day. Chernobyl occurred at night and it was down to human error.

Question 24

Should you rotate shifts slowly or fast?

Answer 24

Czeisler recommended a slow rotation, for example spending three weeks on each shift. Bambra preferred a fast rotation of just 3 - 4 days on each shift so the body never has time to adjust to the new cycle.