Biological Rhythms

Question 1

What are biological Rythms

Answer 1

A biological rhythm is any change in a physiological activity that repeats periodically in a set pattern.

Question 2

What are the three types of biological rhythms

Answer 2

Circadian
One cycle takes approximately a day/24hrs
Metabolic Activity
Hormones/NTs
Sleep/waking
Body temperature

Infradian
One cycle takes longer than 24hrs
Menstruation
Hibernation
SAD

Ultradian
One cycle takes less than 24hrs
Feeding
Stages of sleep
Alertness

Question 3

What is an example of infraction rhythms??

Question 4

What is an example of ultrdian rythms

Answer 4

Sleep/wake cycle

Sleep follows an alternating REM and NREM sleep. This cycle repeats itself every 90 - 100 minutes. We can learn about the sleep stages from recording electrical activity of the brain (Using EEGs).

Stage 1: 4-5% light sleep, muscle activity slows down. Occasional muscle twitching.
Stage 2: 45%-55% Breathing pattern and heart rate slows, slight decrease in body temperature.
Stage 3: 4-6% Deep sleep begins. Brain begins to generate slow delta waves.
Stage 4: 12-15% Very deep sleep. Rhythmic breathing. Limited muscle activity. Brain produces delta waves.
Stage 5: 20-25% REM, Brainwaves speed up and dreaming occurs. Muscles relax and heart rate increases. Breathing is rapid and shallow.

Question 5

What is an example of circadian rhythms

Answer 5

Body temperature fluctuates by up to a degree across a day.

Generally it peaks mid afternoon at about 37.1°C and delines in the small hours (around 4am) to about 36.7°C.

This is influenced by several factors: muscular activity, digestion, heat loss and heat production.

Question 6

What are endogenous pacemakers??

Answer 6

These are internal body clocks that influence the patterns of our biological rhythms. These may be genetic mechanisms.
The help maintain regular rhythms in absence of zeitgebers but they are not perfect and need zeitgebers to synchronise the rhythms to our individual behaviours.
Examples: Pineal Gland & Suprachiasmatic Nucleus

Question 7

What is the role of endogenous pacemakers

Answer 7

Controlling sleep wake cycle
Our internal body clock is found in the hypothalamus and is called the suprachiasmatic nucleus (SCN) – this synchronises our sleep-wake circadian rhythm.
The SCN receives light through the eyes (optic nerve). When light levels drop (at night), this information is received by the SCN causing it to fire impulses to the pineal gland which then secretes melatonin which causes sleepiness.
When light increases (daytime), melatonin levels decrease heavily making us more alert.
Without light as a zeitgeber, the process ‘free runs’ to an average 25hr cycle.

Question 8

What are strengths of endogenous pacemakers

Answer 8

• case study as research support - Summarise the Siffre case study (method and results).
• scientific evidence - Ralph et al. (1990)
  Took the SCN from a ‘mutant hamster’ who had a circadian rhythm which had mutated to 20 hours.
  They transplanted the mutant SCN into the brains of normal adult hamsters.
  The normal hamsters took on the circadian rhythms of the mutant hamsters.
  Despite the shortcomings of less scientific case study research findings, EPs do play an important role in regulating the sleep-wake cycle.
• practical applications = Shift work has been found to lead to a desynchronisation of circadian rhythms and can cause adverse cognitive and physiological effects
  Eg. research has shown shift workers have a lapse of attention at 6am increasing the likelihood of accidents. Additionally, shift workers are 3x more likely to experience heart disease.
  Knowledge of EP and EZ could have applications in terms of educating employers in ways of preventing accidents and ensuring medical care of shift workers. It could also have implications for the economy.

Question 9

What are the weaknesses of endogenous pacemakers

Answer 9

• case study methodology
  = Brief summary of Siffre’s method and the issue with his only participant being himself: generalisability / representativeness / androcentric / ethnocentric / population validity / external validity.

Question 10

what are exogenous pacemakers?

Answer 10

These are external stimuli which provide information about elapsed time and prompt changes in bodily activity and the patterns of our biological rhythms.
Examples- social cues (meal times etc) and light

Question 11

explain the case study of Siffre?

Answer 11

A French cave explorer, Michel Siffre, spent 6 months in an underground cave in Texas in 1972, separated from natural light / dark cycles.

This allowed him to investigate what happens when the bodily sleep-wake cycle is allowed to ‘free run’ away from exogenous zeitgebers.
He was wired up so that various bodily functions could be recorded. He ate and slept whenever he wanted.

At first, his sleep-wake cycle was very erratic, but settled down to a fairly regular pattern of between 25 and 30 hours, that is slightly longer than the ‘normal’ 24-hour cycle. What was actually 179 days, felt like 151 to him.

Question 12

what are the strengths of exogenous pacemakers?

Answer 12

• supporting research = vetter
• practical application = same for shift workers

Question 13

what are the weaknesses of exogenous pacemakers?

Answer 13

• individual differences= Age has an impact on how much sleep people need which in turn may influence how they respond to EZ’s and how their EP’s function (older people need less sleep than younger people).
  Personality also seems to play a role in levels of alertness at certain times of day which again might influence how they respond to EZ’s and how their EP’s function.
• contradicing evidence = luce and segal