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.

Question 9

What are endogenous pacemakers?

Answer 9

• Endogenous pacemakers are internal mechanisms that govern biological rhythms in particular the circadian sleep/ wake cycle.
• Although EP are internal biological clocks, they can be altered and affected by the environment.
• The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep-wake cycle.

Question 10

What are exogenous zeitgebers?

Answer 10

• Exogenous zeitgebers influence biological rhythms.
• These can be described as environmental events that are responsible for resetting the biological clock of an organism.
• They can include social cues, such as meal times and social activities, but the most important zeitgeber is light, which is responsible for resetting the body clock each day, keeping it on a 24- hour cycle.