Circadian rhythms and biological rhythms

including circadian, infradian and ultradian and the difference between these rhythms + the effect of endogenous pacemakers and exogenous zeitgebers on the sleep/ wake cycle

what is a circadian rhythm?

biological rhythms that occur over a 24-hour period

what is a biological rhythm?

patterns of changes in body activity over cyclical periods

what is a ultradian rhythm?

biological rhythms that occur less than one cycle in 24 hours

what is an infradian rhythm?

biological rhythms that occur more than one cycle in 24 hours

give some examples of infradian rhythms.

• menstrual cycle

• seasonal affective disorder (SAD)

which gender does SAD occur more in?

women

what happens to people with SAD?

people become severely depressed in the winter months - typically due to a lack of sunlight

how long does the menstrual cycle last?

about a month (23-36 days)

when does ovulation happen in the menstrual cycle, what happens during it, and how long does it last?

halfway through cycle

oestrogen peaks

lasts 16-32 hours

what happens after ovulation in the menstrual cycle?

progesterone levels increase to prepare for possible implantation of embryo

who conducted a study on the role of exogenous cues on the menstrual cycle?

russell et al. (1980)

what did russell et al. (1980) find in his study on the role of exogenous cues on the menstrual cycle?

• daily sweat samples from one group of women rubbed into upper lip of second group

• groups kept separate

• 68% of their menstrual cycles synced up, showing role of pheromones in synchronising women’s periods

who conducted research to find out whether sleep patterns could be attributed to biological patterns?

tucker et al. (2007)

what did tucker et al. (2007) find in his research about whether sleep patterns could be attributed to biological patterns?

• Ps studied over 11 consecutive days

• individual differences in sleep patterns were biologically driven

what is an endogenous pacemaker?

internal body clocks that regulate biological rhythms

what is an exogenous zeitgeber?

external cues that influence our biological rhythms

what is a limitation of research into endogenous pacemakers and exogenous zeitgebers?

limited when research always views them as separate → they should be viewed holistically

how do exogenous zeitgebers affect babies?

babies initially have random sleep/wake cycle

they are entrained by about 16 weeks

what does our circadian rhythm do?

regulates a number of bodily processes such as sleep/wake cycles and core body temperatures

why are circadian rhythms no different in blind people than sighted people?

connections exist between the SCN and the eye that also affect the sleep/wake cycle and are the same in both sighted and blind people

what is free running sleep?

going to sleep and waking up whenever you want

define entrainment.

the body has mechanisms to synchronise with the external environment

what is a zeitgeber?

a time giver

who conducted animal research into the role of the SCN in chipmunks?

decoursey et al. (2000)

what did decoursey et al. (2000) find in their research into the role of the SCN in chipmunks?

• destroyed SCN connection in brains of 30 chipmunks + returned to natural habitat for 80 days

• sleep/wake cycle in chipmunks had disappeared

• significant number of them had been killed because of this

what are the two types of cycles that occur during sleep?

REM and NREM

how often to sleep cycles repeat?

every 90-100 mins

what are the 5 stages of the sleep cycle, and what happens to the body during each?

stage 1 → NREM, light sleep

stage 2 → NREM, breathing/heart rate slows

stage 3 → NREM, deep sleep, delta waves produced

stage 4 → NREM, very deep sleep

stage 5 → REM, dreaming occurs, increase heart rate

what does a speleologist do?

someone who studies caves

what parts of our body does the circadian rhythm control?

• eating

• sleeping

• mating

• bowel movement suppression

• testosterone secretion

where is the main regulator of our circadian rhythm?

hypothalamus

what is the superchiasmatic nucleus (SCN)?

our biological clock that is dictated by a group of nerve cells in the hypothalamus which is connected to our optic nerves

what happens when the optic nerve senses light?

the SCN sends signals to:

• raise temperature

• raise heart rate

• raise blood pressure

• delay release of sleep hormones like melatonin

what happens when our body temperature rises in the morning?

memory, alertness and concentration sharpen/are at optimal levels

when is our desire to sleep the strongest?

2am-4am and 2pm-3pm

what health issues can a disruption to our natural rhythms lead to?

• diabetes

• depression

• obesity

• dementia

what is the value of understanding circadian rhythms for society?

peak times during day/night when drugs are most effective = understanding of circadian rhythms means we can maximise effectiveness + less likely to need prescriptions

where is melatonin released from?

pineal gland

who conducted a case study on circadian rhythms and what was it?

siffre studying his own biological rhythms

stayed in a cave and partook in free running sleep

found that his natural circadian rhythm settled to just over 24 hours

what is a limitation of siffre’s circadian rhythms case study?

lacks reliability → siffre used artificial lighting in the cave (confounding variable) = debatable whether it was truly free running sleep or not

+ case studies are idiographic = hard to generalise

who conducted a sample study on circadian rhythms?

aschoff and wever (1976)

what did aschoff and wever (1976) do in their study of circadian rhythms?

convinced a group of Ps to spend 4 weeks in a WW2 bunker

all Ps natural circadian rhythms were between 24-25 hours