Biological rhythms

Question 1

Define biological rhythms

Answer 1

• Cyclical patterns within biological systems that have evolved in response to environmental influences.
• 2 key factors that govern biological rhythms:
  1. Endogenous pacemakers (internal)= biological clocks.
  2. Exogenous zeitgebers (external)= changes in the environment.

Question 2

What is a circadian rhythm?

Answer 2

• 24 hour (‘body clock’).
• Reset by levels of light.
• Examples= sleep-wake cycle and body temp.

Question 3

What is the sleep- wake cycle?

Answer 3

• Dictates when we are awake and asleep.
• Light= primary input (exogenous zeitgeber).
• Eye detects light- suprachiasmatic nuclei- coordinate entire circadian system.
• Also controlled by homeostasis.
• Homeostasis tells the body there is a need for sleep because of energy consumption.
• Homeostatic drive for sleep increases throughout the day.

Question 4

Evaluation for circadian rhythms

Answer 4

1. Research support= Siffre.
2. Individual differences= morning people vs evening people.
3. Temperature may be more important than light= suggests that we should take holistic approach.

Question 5

Siffre study

Answer 5

• Found that the absence of external cues significantly altered his circadian rhythm.
• When he returned from an underground stay with no clocks or light, he believed the date to be month earlier than it actually was.
• Suggests that his sleep-wake cycle had been influenced by the lack of external cues.

Question 6

What are infradian rhythms?

Answer 6

• Last longer than 24 hours.
• Occur weekly, monthly, annually etc.
  e.g. the female menstrual cycle.
• Regulated by hormones that either promote ovulation of stimulate the uterus for fertilisation.
• Ovulation occurs halfway through cycle (when oestrogen is the highest).
• Avg. menstrual cycle= 28 days.

Question 7

Evaluating Infradian rhythms

Answer 7

1. Research support (governed by exogenous zeitgebers)= women spent 3 months in cave, only a small lamp for light. Menstrual cycle shortened from 28 days to 25.7 days. Suggests light effects menstrual cycles.
2. Research support (exogenous zeitgebers)= menstrual cycles synchronised through odour exposure. Sweat on upper lip- MC’s synchronised, pheromones on other people= more holistic approach should be taken

Question 8

What are ultradian rhythms?

Answer 8

• Fewer than 24 hours.
• Human sleep.
• REM and NREM sleep.
• 5 stages of sleep (light sleep, deep sleep, REM sleep).
• REM sleep is where dreaming occurs.
• Repeated every 90 mins.
  x5 cycles during the night.