Biologicsl Rhythms

Question 1

What is a biological rhythm?

Answer 1

any change in a physiological activity that repeats periodically in a set pattern

the frequency they change determines what type of cycle it is

Question 2

What is a circadian rhythm?

Answer 2

one cycle that occurs approx. every 24 hours (i.e. sleep/wake cycle)

Question 3

What is an infradian rhythm?

Answer 3

one cycle that occurs longer than 24 hours (i.e. menstrual cycle)

Question 4

What is an ultradian rhythm?

Answer 4

one cycle that occurs less than 24 hours (i.e. stages of sleep)

Question 5

How is the menstrual cycle considered to be an example of an infradian rhythm?

Answer 5

follicular phase - phase lasts from 10-14 days, starting with 1st day of menstruation. oestrogen and progesterone levels are at their lowest. when bleeding stops, the follicular phase begins causing the endometrium to thicken. FSH levels rise causing maturation of ovarian follicles

ovulatory phase - FSH signals ovaries to produce oestrogen , stimulating LH levels to surge around day 14. lasts approx 14 days.

Question 6

how is body temperature considered to be an example of an circadian rhythm?

Answer 6

• temperatures fluctuates by up to a degree across a day
• generally, it peaks mid afternoon at 37.1 and troughs in the small hours (4am) at about 36.7
• influences by several factors, muscular activity, digestion and heat loss/production

Question 7

What is the sleep/wake cycle?

Answer 7

lasts approx. 24 hours that determines our pattern of wakefulness and sleepiness.

dips and rises at certain times of the day and is influenced by internal and external factors known as endogenous pacemakers and exogenous zeitgebers.

Question 8

What are endogenous pacemakers?

Answer 8

internal body clocks that influence the patterns of our biological rhythms.

help maintain regular rhythms in absence of zeitgebers but they are not perfect and need zeitgebers to synchronize the rhythms to out individual behaviors

Question 9

What are examples of endogenous pacemakers?

Answer 9

pineal gland
suprachiasmatic nucleus (SCN)

Question 10

How does the suprachiasmatic nucleus (SCN) have a role in controlling the sleep/wake cycle?

Answer 10

• located in the hypothalamus

- responds to light levels and not just via the eyes

Question 11

How does the pineal gland have a role in controlling the sleep/wake cycle?

Answer 11

• located in the endochrine glands

- secretes melatonin

Question 12

How does the suprachiasmatic nucleus (SCN) and pineal gland work together to have a role in controlling the sleep/wake cycle?

Answer 12

• theres is a direct neural pathway between the SCN and the pineal gland
• decreasing light levels are detected by the SCN and it fires impulses to the pineal gland which increases melatonin secretion

Question 13

How does melatonin have a role in controlling the sleep/wake cycle?

Answer 13

• secreted by the pineal gland to increase levels of melatonin, making us feel drowsy
• levels rise sharply as light levels drop and stay elevated all through the night and then falls back to day time levels around 9

Question 14

What are exogenous zeitgebers?

Answer 14

external stimuli which people provide information about elapsed time and prompt changes in bodily activity and patterns of our biological rhythms

Question 15

What is the role of exogenous zeitgebers on the sleep/wake cycle as demonstrated in Siffre’s research

Answer 15

Siffre spent 6 months in an underground cave in Texas, separated from natural light/dark cycles.
This allowed him to investigate what happens when the bodily sleep/wake cycle is allowed to ‘free run’ away from exogenous zeitbegbers.

he was wired up so that various bodily unctions could be recorded. he ate and slept when ever he wanted