Circadian Rhythms

Question 1

Info About General Rhythms

Answer 1

• All living organisms have biological rhythms which influence how our body systems behave
• These rhythms are governed by endogenous pacemakers (internal biological ‘clocks’) and exogenous zeitgebers (external environmental changes)
• These rhythms can occur many times during a day (ultradian), take longer than a day to complete (infradian), or last for around 24h (circadian)

Question 2

Circadian Rhythms Definition

Answer 2

• Daily rhythms that are adjusted (entrained) to the environment by external cues like daylight + they synchronise behaviour and body states with environmental changes

Question 3

What signals determine our sleep and wake times?

Answer 3

• Light and darkness

Question 4

Rhythm Dips & Rises

Answer 4

• The C.R dips and rises at different times of the day so our strongest sleep is usually between 2-4am and 1-3pm
• Sleepiness we experience during these circadian dips is less intense with sufficient sleep and more intense when sleep deprived

Question 5

Involvement Of Homeostasis

Answer 5

• When we have been awake for long periods of time, homeostasis tells us that the need for sleep is increasing because of the amount of energy used up during wakefulness
• This drive for sleep increases gradually throughout the day, reaching its maximum in the late evening when most people fall asleep
• The C.R keeps us awake as long as there is daylight prompting us to sleep if its dark

Question 6

What is the circadian system intolerant of?

Answer 6

• Any major altercations in sleep and wake schedules because this causes the biological clock to become completely out of balance, hence the need to adapt to new time zone quickly

Question 7

SCN (Suprachiasmatic Nucleus) & Melatonin

Answer 7

• Small group of brain cells also known as the body clock (main endogenous pacemaker)
• SCN causes the pineal gland to release melatonin (reduces brain activity and makes us sleepy) – happens when the optic nerve reduces its activity as night falls
• Melatonin production stops when activity on the optic nerve increases with daylight levels

Question 8

Siffre’s Cave Study Procedure & Findings

Answer 8

• Spent long periods of time living underground in order to study his biological rhythms
• Had no external cues to guide his rhythms, with only influence on his behaviour being his internal ‘clock’ or ‘free running rhythm’
• His experiences showed that the free-running cycle settles down to a regular rhythm which is just over 24h

Question 9

Siffre’s Cave Study Limitations

Answer 9

• The study was of one individual and therefore had unique features
• His body’s behaviour may not be typical of all people
• Living in a cave may have particular effects due to factors like temperature
• Key variables were controlled to observe their effects on the cycle
• Despite the fact that these issues mean if may not be possible to generalise the findings, there have been subsequent studies above ground that have confirmed the findings of research in cave environments

Question 10

Aschoff & Wever (1976)

Answer 10

• Convinced a group of participants to spend 4 weeks in a WW2 bunker deprived of natural light
• All but 1 of the participants (whose sleep/wake cycle extended to 29hrs) displayed a circadian rhythm between 24 and 25hrs
• Both Siffre’s study and this study suggest that the natural “sleep/wake cycle” may be slightly longer than 24hrs but is entrained by exogenous zeitgebers associated with our 24hr day

Question 11

Folkard et al (1985)

Answer 11

• Studied a group of 12 who agreed to live in a dark cave for 3 weeks, going to bed when the clock said 11:45pm and waking up when it said 7:45am
• Over the course of the study, the researchers sped up the clock, so a 24hr period actually lasted for 22hours
• Only 1 participant accepted this new time period, showing proof that a circadian rhythm cannot be overridden by exogenous zeitgebers