Circadian Rhythms

Question 1

The earth synchronizes our internal clock. True/false

Answer 1

True. The period is not under selection pressure but the phase

Question 2

The internal clock is exactly 24 hours. True/ false

Answer 2

False. The internal clock is NOT exactly 24 hours

Question 3

What is an example of behaviour of a plant that shows that circadian clocks help anticipate environmental cycles?

Answer 3

Sunflower leaves orientate towards the position of the sun. During the night, when the sun isn’t there, the leaves move towards the East anticipating sunrise

Question 4

What are examples of rhythmic hormones?

Answer 4

cortisol

melatonin

Question 5

Which hormone prepares the body from horizontal to vertical position?

Answer 5

Cortisol, for higher heart rate hence rises just before morning

Question 6

Which hormone is only secreted when it’s dark?

Answer 6

melatonin- not a sleep hormone, secreted by pineal gland, used to treat jetlag

Question 7

Why is the incidence of heart attacks and stroke highest between 6 am and 12 pm?

Answer 7

Due to increased levels of cortisol, increased heart rate may lead to high incidence of cardiovascular attacks

Question 8

Why is it that in rheumatoid arthritis, pain and stiffness is greatest in the morning? And how can treatment optimize this timing?

Answer 8

Pro inflammatory cytokine rhythm peaks at 4 am. Treatment with glucocorticoids at 3/4 am to supress the immune system

Question 9

When are asthma attacks most severe?

Answer 9

midnight

Question 10

Define pharmacokinetics/ dynamics

Answer 10

kinetics: what the body is doing to the drug ie absorption/metabolism
dynamics: what the drug is doing to the body, whether the target structures of the drugs are rhythmic eg cox enzymes for asprin

Question 11

French scientist that found out that mimosa leaves are upright during the day and drooped in darkness

Answer 11

De Marian

Question 12

Founding father of chronobiology

Answer 12

Jurgen Aschhoff- investigated in a constant darkness ie WW2 bankers in Munich, having a low core body temperature correlated with sleep

Question 13

What is the endogenous circadian period?

Answer 13

Approxiamtely 1 day can be 24.1 hours

Question 14

Circadian clocks are endogenous self sustained oscillators. True/ false

Answer 14

True

Question 15

Fundamental properties of circadian clocks

Answer 15

are endogenous, self-sustained oscillators
free running period/tau is close but not exactly 24 hours
Free-running periods are temperature compensated
rythmic environmental stimuli entrain circadian clocks

Question 16

What is the master clock?

Answer 16

Suprachiasmatic nucleus SCN located in the hypothalamus above the optic chiasm

Question 17

Evidence of the SCN being the master clock

Answer 17

loss of overt circadian rhythms in SCN lesions
transplantation of fetal SCN tissue in SCN lesioned arrhythmic host restores locomotor activity
Genotype of donor SCN determines circadian rhythm of host
SCN explants-neurons show self sustained circadian oscillations

Question 18

How is the SCN linked to the retina?

Answer 18

retinohypothalamic tract

Question 19

Circadian oscillator is cell autonomous.true/false

Answer 19

true. Each individual SCN neuron will have a 24 hr circadian rhythm as well as cell autonomous ie self sustaining

Question 20

In which peripheral cells is the SCN also present

Answer 20

liver, kidneys. peripheral organs also show circadian rhythm

Question 21

How is oscillation generated?

Answer 21

By -ve feedback. TF (+ve elements) activate transcription of mRNA into clock genes , which are negative elements eg period 1, 2, cry 1, that inhibit the transcription factors hence negative feedback.
-ve feeback loop causes delay hence oscillations

Question 22

How do geneticists investigate molecular clockwork?

Answer 22

forward and reverse genetics

forward: from phenotype to gene eg id of the clock gene
reverse: from gene to phenotype eg differential function of the 2 cry genes

Question 23

In mammals, light synchronizes circadian clock with the environment. True/ false

Answer 23

true. retina to SCN to regulation of physiology and synchrony of peripheral clocks

Question 24

What is a chronotype

Answer 24

popensity of an individual to sleep at a particualr time during a 24 hour period. behavioural manifestation underlying circadian rhythms of physical processes

Question 25

Define scissors of sleep

Answer 25

sleeping patterns on free days different from work days. sleep longer on free days to compensate for shorter sleep duration during work days eg for late chronotypes

Question 26

for the early birds, light needs to delay because they have a fast circadian clock. True/false

Answer 26

True. fast circadian clock delay needs to be bigger than advance

Question 27

for night owls, light needs to advance because they have a slow circadian clock/ True/false

Answer 27

true. slow circadian clock. Advance needs to be bigger than delay

Question 28

Define entrainment

Answer 28

synchronization of the endogeneous oscillator to the light/dark cycle of the environment

Question 29

how do rhythmic environmental stimuli entrain circadian clocks

Answer 29

period of the biological rhythm becomes equal to the external Zeitgeber rhythm with a stable phase angle

Question 30

Which two processes regulate the timing of sleep

Answer 30

circadian process C

homeostatic process S- sleep dependent