Biological Rhythms

Question 1

What is a circadian rhythm?

Answer 1

Last approximately 24 hours such as sleep wake and body temperature cycles.

Question 2

Explain the sleep-wake cycle.

Answer 2

Internal body clock called SCN, just above the optic chiasm controlling the cycle. Receives light from optic nerve even when eyes are closed. As light decreases, sends a signal to pineal gland to release melatonin which reduces brain mechanisms keeping us awake = sleepy. When light increases at dawn SCN picks this up and melatonin decreases = awake

Question 3

How is the PERIOD3 gene implicated in the sleep-wake cycle?

Answer 3

It comes in different forms, producing a slightly different circadian rhythm. Can explain individual differences.

Question 4

What are the endogenous pacemakers and exogenous zeitgebers in the sleep wake cycle?

Answer 4

Endogenous: SCN, pineal gland, melatonin.
Exogenous: light, noise, alcohol, social factors like eating patterns, socialising, work patterns.

Question 5

Evaluate the sleep- wake cycle. (SSPP)

Answer 5

S - mutant hamsters bred to have 20 hour sleep wake cycle + cells from SCN implanted into other hamsters - their sleep wake cycle reduced.
S - siffre spent 7 months in a cave with no external lights and developed a 25 hour sleep cycle even w no clocks or light. He still knew when to wake up and fall asleep due to internal body clock
P - shift workers have to be more awake at night - strategies like sleeping in pitch black and working in bright light helps (economy)
P - chrono-therapeutics = how timing can effect drug efficacy. Certain times when drug most effective associated w circadian rhythm. Risk of heart attack higher after wake up - developed drugs taken before bed that release when you wake up.

Question 6

What is the body temperature cycle?

Answer 6

Normal temperature is 37 degrees over 24 hours. It varies on a regular pattern - lowest at 4am highest at 6pm. Maintained through homeostasis. Rhythm is due to external temp and clock in SCN different to sleep wake cycle (found from nurses on shift w different sleep wake cycles but not body temp). Sleep = body temp. Drops off when we start to fall asleep, starts to rise when we wake up.

Question 7

What are the endogenous pacemakers and exogenous zeitgebers for the core body temperature circadian rhythm?

Answer 7

Endogenous: homeostasis, clock in SCN
Exogenous: external temp

Question 8

Give a practical application of the core body temp rhythm.

Answer 8

Impacts concentration levels. Circadian trough occurs between 4-6am and associated w poor conc. industrial accidents more likely to occur if people work then. Lower body temp linked to poorer cognitive function - attention memory and problem solving. Best time to try learn important info is at times when it is higher - implications on economy.

Question 9

What are infradian rhythms?

Answer 9

Over 24 hours. Like the menstrual cycle and SAD.

Question 10

Explain the human menstrual cycle.

Answer 10

Average = 28 days but can range from 23-36. Characterised by fluctuating hormone levels regulating ovulation. Pituitary gland releases FSH and LH causing a follicle in the ovary to ripen an egg and trigger release of oestrogen. Once egg has ripened, progesterone released which prepares the uterus for pregnancy. If pregnancy doesn’t occur progesterone is reduced and uterus lining is shed.

Question 11

What are the endogenous and exogenous factors of the human menstrual cycle.

Answer 11

Endogenous: FSH, LH
Exogenous: pheromones, odour exposure, alcohol, stress, diet.

Question 12

Evaluate the human menstrual cycle infradian rhythm. (SC)

Answer 12

S - 9 samples of pheromones taken from women with irregular periods. Collected underarm sweat on cotton pad and wiped it on upper lip of other 20 women w irregular periods. 68% experiences changes that synchronised their menstrual cycle with the odour donors. Evolutionary - children at the same time and if woman dies, child will be looked after and survive. (But lacked validity as self report)
C - basketball team of women found no correlation in menstrual cycles.

Question 13

What is SAD?

Answer 13

Seasonal affective disorder. Happens in winter. Depressive symptoms like low mood, lack of interest and reduced activity. Reduced hours of daylight = more melatonin from pineal gland for longer = suppressed serotonin. Low serotonin = depression.

Question 14

What are the endogenous pacemakers and exogenous zeitgebers of SAD?

Answer 14

endogenous: increased melatonin, reduced serotonin
Exogenous: lack of light

Question 15

Give a practical application of SAD.

Answer 15

Phototherapy - light box where bright light given in the morning to treat SAD - 60% success.

Question 16

What are ultradian rhythms?

Answer 16

Less than 24 hours, like the sleep cycle and basic rest activity cycle.

Question 17

Describe the human sleep cycle.

Answer 17

Alternate between NREM (4 stages) and R.E.M. sleep in stages 1-5. 1-2 is light, 3-4 deep sleep, 5 = R.E.M. one cycle = 90 mins and we go through the cycle many times. Researchers characterised stages of sleep by using an EEG. R.E.M. sleep = eeg same as awake but muscles paralysed. NREM sleep = synchronised wave patterns.

Question 18

Describe the research into dreams and R.E.M. sleep.

Answer 18

Monitored EEG if participants so they could be worn up during different phases. R.E.M. sleep = 80% recalled dreaming, compared to 20% in NREM sleep. Research suggests there is a biological clock located in the PONS that influences R.E.M.

Question 19

What are endogenous and exogenous factors of the sleep cycle?

Answer 19

Endogenous : PONs, SCN

Exogenous: alcohol suppressed R.E.M. sleep

Question 20

Evaluate the sleep cycle (SS).

Answer 20

S - 9 participants who had no caffeine or alcohol. When woken during REM they reported dreaming. However artificial environment so not true to real sleep.
S - pps measured for 11 days and nights in controlled environment. Measured sleep duration, time to fall asleep and amount of time in each stage. Consistent variation in sleep, mostly in 3-4. Suggests internal factors important as external factors controlled.

Question 21

What is the BRAC?

Answer 21

Basic rest activity cycle. Cognitive, attention and other physical functions go through peaks and troughs every 90 mins. First half = awake and alert because fast brainwave state. Second half = slow down, last 20 mins = dreamy and possibly tired. Then cycle restarts.

Question 22

What are the endogenous and exogenous factors of the BRAC?

Answer 22

Endogenous: internal biological clock
Exogenous: mealtimes, exercise, behaviour of others

Question 23

Give evaluation for the BRAC. (SSC)

Answer 23

• best violinists performed 3 x a day no longer than 90 mins w breaks in between, same as athletes and chess players
• group of psychiatric patients over 6 hours, found a clear 90 Min cycle in eating and drinking - natural so ecological validity
• unique and small samples

Question 24

How can sunlight specifically affect the sleep wake cycle?

Answer 24

Changes in sunlight levels means the rhythm becomes aligned (entrainment). Also alcohol, noise, social factors affect.

Question 25

Give 4 symptoms of disruption to the sleep wake cycle.

Answer 25

Decreased alertness
Sleep deprivation (sleeping in the day affects R.E.M. sleep - 2 hours less)
Social issues - divorce rates higher in shift workers, not seeing friends
Poor health - increased cardiovascular disease.

Question 26

Give a strength of the exogenous zeitgebers light and social effects

Answer 26

Light - light shone on just back of knees disrupted circadian rhythms. Melatonin = consequences for artificially lit world. Siffres was 25 so maybe we have been entrained to 24 by lights?
Social factors - babies have random sleep wake patterns so maybe entrained to a 24 hour one by parents.