11 - Ultradian and Infradian Rhythmns

Question 1

Define ultradian rhythm. Give an example

Answer 1

Rhythms that span a period of less than 24 hours e.g. the five sleep stages

Question 2

Outline the sleep stages

Answer 2

Alternates between Rapid Eye Movement (REM) sleep (which is stage five) and Non-Rapid Eye Movement (NREM) sleep (which consists of stages one, two, three and four).

Repeats itself every 90 minutes.

Question 3

How does the EEG trace change across the sleep stages?

Answer 3

Deep sleep - brainwaves slow and breathing and heart rate decreases.

Fifth stage (REM sleep) - EEG pattern resembles that of an awake person. It is during this stage that dreaming occurs.

Question 4

Define BRAC

Answer 4

Basic Rest Activity Cycle

The 90 minute cycle found during sleep

Question 5

Outline BRAC and what it means

Answer 5

90 minute cycle continues when we are awake.

During day - move progressively from state of alertness to state of physiological fatigue.

Research suggests that the human mind can focus for about 90 minutes, and towards the end of those 90 minutes the body begins to run out of resources, resulting in loss of concentration, fatigue and hunger.

Question 6

Define infradian cycle and give an example

Answer 6

Cycles that span a period of longer than 24 hours; they may last weeks, months or even a year.

Menstrual cycle - lasts for about a month.

Question 7

How do hormones regulate the menstrual cycle

Answer 7

Ovulation occurs roughly halfway through the menstrual cycle, when oestrogen levels are at their peak, and usually lasts for 16-32 hours.

After ovulation, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus.

Question 8

What are the advantages of ultradian and infradian rhythms?

Answer 8

+ Group of elite violinists studied and found that among this group practise sessions were limited to 90 minutes at a time. Violinists frequently napped to recover from practise, with the best violinists napping more. The same pattern was found among athletics, chess players and writers.

+ Infradian rhythms can affect behaviour. Found that women express a preference for feminised male faces when choosing a partner for a long- term relationship. However, they showed a preference for masculinised faces during ovulation.

Question 9

What are the disadvantages of ultradian and infradian rhythms?

Answer 9

• There are individual differences in sleep patterns, which are biologically determined and may even be genetic in origin. Participants were studied over 11 consecutive days and nights in a laboratory environment. The researchers assessed sleep duration, time taken to fall asleep and the amount of time in each sleep stage. They found differences in all of these characteristics.
• The menstrual cycle is not only governed by infradian rhythms. When several women of childbearing age live together, and do not take oral contraceptives, their menstrual cycles synchronise. In one study samples of sweat were collected from one group of women and rubbed onto the upper lip of another group of women, their menstrual cycles became synchronised. This suggests that the synchronisation is affected by pheromones.