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ANATOMY > CHRONOBIOLOGY > Flashcards

CHRONOBIOLOGY Flashcards

1
Q

what is sleep

A

it is the time in which we are unresponsive to the environment and let our guard down

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2
Q

define circadian rhythms

A

24 hour endogenously driven cycles

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3
Q

what is a chronotype

A

persons preference for morning or evening

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4
Q

how did they study innate circadian rhythms back in the day

A

-in a cave with no external influences
-found the body temp set to a 24 hr cycle and the sleep wake cycle followed this

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5
Q

what is sleep neccessary for

A
  1. immune support
  2. wastage removal
  3. enhanced neural connections
  4. time of caloric restriction
  5. restore brain and energy stores
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6
Q

physiology of circadian rhythms

A

-they are 24 hours 11min +-16min
-endogenously driven by interacting clock genes that are found in your master clock: SCN

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7
Q

what are the clock genes

A

PER
CLOCK
REV-erba
CRY
BMAL-1

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8
Q

what entrains your circadian rhythm

A

-zeitgebers
-these include light, meal timing, locomotor activity

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9
Q

4 criteria for circadian rhythms

A
  1. endogenous( rhythm runs without entrainment)
  2. must repeat once a day
  3. entrainable
  4. rhythmicity of the circadian rhythms persists over a range of physiological temperatures
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10
Q

give some examples of circadian rhythms

A
  1. body temp
  2. blood pressure and heart rate
  3. sleep wake cycle
  4. hormone release
  5. meal timing
  6. physical and cognitive performance
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11
Q
  1. blood pressure circadian rhythm
A

-blood pressure seems to lower at night and rise upon waking

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12
Q
  1. heart rate
A

-heart rate has a very robust rhythm besides in the face of exercise where it increases
-heart rate has shown to be lower in sleeping hours

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13
Q
  1. body temperature
A

core temp peaks around late afternoon and then falls and starts to rise upon waking again
-lowest at night

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14
Q
  1. melatonin
A

melatonin production starts around 2 hours before bedtime and increases until it peaks in the middle of the night and then falls to normal daytime lows in the early morning

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15
Q
  1. cortisol
A

-increased synthesis post prandially
-as it helps in meatbolism

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16
Q
  1. growth hormone
A

-large sexual dimorphism
-but in general secreted at night and decreases in the day
-it is released from the anterior pituitary in response to GHRH and somatostatin

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17
Q
  1. testosterone
A

has a low amplitude circadian rhythm so there is no large diurnal difference
-but it is higher at night and has episodic bursts of secretion

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18
Q

2 significant purposes of these biological circadian rhythms

A
  1. to ensure that all systems within the body are in synch
  2. to ensure the organism is in synch with the outside world
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19
Q

what is the main controller of the circadian rhythms

A

the master clock ie; the suprachiasmatic nuclei(SCN)

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20
Q

More about the SCN

A

-has 20000 neurons
-each with its own circadian oscillator.
-the oscillators are all synchronised so as to give a synchronised rhythm ie; oscillate coherently
-the SCN recieves photic output from the retina directly ie; is entrained

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21
Q

the peripheral clocks

A

-these lie spread throughout tissue in the body
-are under control of the master clock
-will become desynchronized if not under control by the master clock
-the master clock controls the peripheral clocks directly and indirectly by co ordinating neural and humoral signals

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22
Q

the pineal gland

A

-clock found in the brain
-it releases melatonin to the rest of your body where melatonin receptors are found
-it is controlled by the SCN ie; it connects the nervous system with the endocrine system by converting nerve signals from the SCN into hormone signals

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23
Q

the pinealocytes

A

-these are large irregularly shaped cells that that produce melatonin but do not store it; ie; the melatonin is released immediately after production
-produced in response to nerve signals from the SCN
-melatonin has a short half life
-we know it is released at night and is influenced by the light dark cycle

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24
Q

how can we measure melatonin levels

A

-directly in saliva and plasma

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25
Q

what does the level of melatonin in the body help tell us

A

the measure provides a direct estimate of the functioning of the SCN

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26
Q

the circadian endocrine intercept

A

this intercept explains the time of day dependent release and production of many hormone

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27
Q

what is cellular hormone action governed by

A
  1. the concentration of the hormone in relation to its relative affinity for a specific receptor
    2.the availability and abundance of the relative receptor
    3.the activity of post receptor signalling components
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28
Q

melatonin over life spans

A
  1. post birth- no melatonin is produced
  2. after 6-8wks- see a robust melatoning rhythm
    3.melatonin reaches a lifetime peak around 5 years old
  3. then it declines to a stable adult mean after puberty
    5.then after 40 years old stably declines again
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29
Q

highs and lows

A

14:30= best co ordination
17:00=best cardiovascular and muscular efficiency and performance
18:00=highest body temp
20:00=melatonin secretion
04:00 lowest body temp
07:00=melatonin stops
10:00=greatness cognitive performance

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30
Q

how do we measure chronotype

A

using the horne osteberg personality questionare
-if you are a morning type your acrophases are phase advanced
-if you are an evening type your acrophases are phase delayed

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31
Q

how would you measure your natural circadian rhythm

A

use constant routine protocol

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32
Q

pros and cons of a constant routine protocol

A

PROS
1. currently the gold standard
2. can see the difference between natural and entrained rhythms
CONS
1.expensive
2.impractical
3.time consuming

33
Q

what is the phase angle of entrainment

A

-this is the temporal relation between the external cues and the innate circadian rhythms/clock
-the greater the angle of entrainment the greater the misalignment between the natural circadian clock and external cues
ie; sleep wake cycle is misaligned from the 24hr light dark cycle
-this leads to increased risk of daytime sleepiness, sleep disruption and GI problems

34
Q

what 2 processes regulate sleep

A
  1. circadian rhythms
    -the SCN generates 24hr sleep wake rhythms
    2.sleep homeostat
    -it is an hourglass oscillator
    -accumulation of sleep pressure decreases with more sleep
    -it also tracks the history of sleep to calculate sleep debt
    -controls sleep duration and intensity
35
Q

what are the 2 paths for wakefulness

A
  1. ventral pathway
    -wake promoting populations innervate the hypothalamus to stimulate transmission of sensory info to the cortex
    2.dorsal pathway
    -wake promoting populations innervate the hypothalamus and the forebrain to excite the cortex
36
Q

steps to waking the brain

A
  1. branch 1 is where the pons produces acetylcholine which activates areas of the thalamus responsible for channeling signals to the cortex which is the site of conciousness
    2.in branch 2 neurotransmitters produced in the pons and hypothalamus will prime the cortex so it can recieve signals from the thalamus
  2. in the third branch orexins in the hypothalamus are produced to maintain the arousal system
37
Q

how does the brain tire

A
  1. then as the brain is aroused, ATP is broken down causing a build up of adenosine
  2. the adenosine triggers the VLPO
  3. The SCN also fires neurons to the VLPO
  4. when the VLPO is activated it releases GABA and galanin.
  5. GABA and galanin will bind to receptors in the hypothalamus and the pons and inhibit the arousal system
38
Q

methods used to measure sleep

A

polysomnography
measures:
1. EEG-brain
2.EMG-muscle
3.EOG-eye
4.ECG-heart

39
Q

what are the stages of sleep

A
  1. REM
  2. NON REM 1,2 and 3
40
Q
  1. wakefulness
A

the EEG has alpha waves of 8-13 cps

41
Q

non rem 1

A

NREM 1 is the first stage we enter
-characterized by theta waves of 4-7cps
-low frequencing
-NREM 1 is the stage in which we are most likely awoken by low intensity stimuli
-only makes up 5% of sleep

42
Q

non REM 2

A

-makes up majority of our sleep
-ie 50%
-theta waves
-made up of K complexes and sleep spindles
-K complexes arise when we are exposed to the same low intensity stimuli that would have woken us up in NREM 1

43
Q

non REM 3

A

-makes up 20-25% of our sleep
-slow wave sleep
-period of muscle repair and recovery

44
Q

REM sleep

A

-this makes up 20-25% sleep
-muscle paralysis, dream phase with high brain activity
-period of pyschological recovery

45
Q

sleep stage distribution

A

NREM1: 5%
NREM2: 50%
NREM3: 25%
REM: 20%

46
Q

what is considered healthy sleep

A
  1. no daytime sleepiness or naps needed
  2. sleep feels restorative
  3. constant duration and timing
  4. sleep in sync with circadian clock
  5. sleep in sync with the environment
  6. no catch up sleep
47
Q

how do circadian rhythms change over lifespans

A

-phase advance by 0.5 hours every decade from adulthood onwards

48
Q

altered SCN function with age

A
  1. change in electrical activity of the SCN
  2. reduction in the circadian output rhythm amplitude
49
Q

possible reasons for the altered SCN function with age

A
  1. change in the properties of the SCN cell membrane with age which changes the electrical activity of the cells
  2. altered synchrony of the neuron oscillators so no robust rhythm is produced
  3. the molecular clockwork itself is altered with age
50
Q

melatonin changes with age

A

-production decreases with age
-which decreases the amplitude of the sleep wake cycle in elderly so they find it difficult to distinguish between sleep and wake

51
Q

light changes with age

A

-eyes let less light in or older people might spend less time in natural light
-so there is less light entrainment of the circadian system

52
Q

important changes across lifespans

A
  1. newborns produce no melatonin
    -they show polyphasic sleep ie; build up 14 hrs through 2-4hr naps
    -newborns start in REM not in NREM sleep
    2.infants start producing melatonin and so circadian rhythms start to show
    3.in young children(6-11years)
    -see chronotypes begin to emerge as societal structures are put into place
    -very deep sleep to support growth
    -high waking brain activity
53
Q

adolescent sleep

A
  • constant sleep debt
    -often doing catch up sleep
  • often have poor entrainment of their circadian clocks
    -timing delays ie; takes longer to fall alseep and longer to wake up
    -max delay reached at around 20 years old
54
Q

why do adolescents experience a delay in their sleep timing

A
  1. biological factors
    -they dont accumulate as much sleep pressure
    -they are phase delayed
    2.environmental factors
    -less parent enforcement on bed time
    -screen time
    -sport and homework
55
Q

most common sleep disorder in adolescents

A

delayed sleep phase syndrome
-natural clock is delayed

56
Q

sleep changes in adults

A
  1. reduced sleep wake amplitude
  2. reduced non rem 3 ie; slow wave sleep
  3. spend more time in bed overall
  4. decreased REM sleep
  5. phase advanced
  6. in older adults zeitgebers appear to be less effective and they are even more phase advanced
57
Q

what is the most common sleep disturbance in olrder adults

A

insomnia

58
Q

what causes insomnia in older adults

A
  1. medications
  2. depression
  3. pyschological distress
59
Q

what 4 other sleep disorders besides insomnia are common in the elderly

A
  1. sleep apnoea
  2. restless leg syndrome
  3. periodic limb movement syndrome
  4. REM sleep behavior disorder
60
Q

what is REM sleep behaviour disorder

A

this is when there is enhanced motor activity in REM sleep instead of muscle paralysis
ie; sleep walking/ talking/ eating

61
Q

what 2 factors should one consider in about circadian rhythms with regards to performance

A
  1. chronotype
  2. habitual training time
62
Q

what is diurnal variation in performance

A

when different individuals perform best at different times of the day depending on chronotype and habitual training times

63
Q

what results have been found from studies done on diurnal variation

A
  1. saw majority of athletes are more bias towards a morning chronotype( even if their genotype isnt 5/5 PER3 VNTR)
  2. ie; they found no genotype-chronotype association when it comes to preferred training hours
  3. so it could be said that genotypes 4/4 with evening chronotypes have preferred morning performance because their habitual training has shifted their preference from evening to morning
64
Q

the insomnia scale

A

insomnia can range from mild to severe
-mild insomnia would be when you have SOL a few nights a week(takes around 30 minutes to fall asleep) and has limited daytime dysfunction
-severe insomnia would be SOL every night with severly impaired daytime dysfunction

65
Q

2 types of insomnia

A
  1. transient -temporary
    -usually due to stress, poor sleeping environment or jetlag
  2. persistent- more than 3 months
    -usually due to a circadian problem or pyschological disorders like depression
66
Q

2 types of sleep apnoea

A
  1. central
    - fail to pull air into the lungs
  2. obstructive
    -upper airways collapse so air cannot pass into the lungs
67
Q

what is the circadian dysrhythmia sleep disorder

A

this is when either your innate circadian clock is misaligned from environmental cues or your central clocks are desynchronized from your peripheral clocks

68
Q

what can cause circadian dysrhythmia

A
  1. shift workers
  2. travel jetlag
  3. social jetlag
  4. blindness
69
Q

jetlag

A
  • cross 3 or more time zones so your circadian clock cannot adapt which leads to circadian dysrhythmia
    -not along a N-S travel
    -more severe when travelling from W-E than it is when travelling E-W
70
Q

what does the intensity of jetlag symptoms depend on

A
  1. direction of travel
  2. how well you were able to sleep on the flight
  3. the intensity of the external cues upon arrival
  4. number of time zones crossed
71
Q

travelling to the WEST

A
  • phase delayed
72
Q

travelling to the EAST

A

-phase advanced

73
Q

how does one treat jetlag

A
  1. resynchronize the body clock
  2. medication
  3. prescribed sleep schedule
74
Q
  1. resynchronising the body clock with light
A

to phase delay the body clock when travelling west:
1. expose yourself to light during your home time evening hours

to phase advance when travelling east:
2. begin light exposure in the late evening until the early morning

75
Q
  1. medication to reset the body clock
A

melatonin will help adjust to new time zone but must be used with light exposure
-to phase delay it makes sense to take it in your home time morning hours
-could use sleep sedatives but these wont correct the circadian misalignment they will just help with the sleep deprivation n

76
Q
  1. prescribed sleep schedule
A

this is when you shift your sleep schedule either direction by an hour for 3-5 days prior to the travel

77
Q

blindness

A

have a free running sleep wake cycle as they are not light entrained and so must take melatonin

78
Q

seasonal affective disorder

A

when a persons circadian rhythm becomes misaligned due to the shortening of the photoperiod

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