Circadian Rhythms Flashcards
External cue that synchronizes or helps entrain (determine or modify) an organisms internal clock
Zeitgeber (time giver)
What happens to melatonin levels as per and Tim drop?
Melatonin increases
What happens when an SCN of one animal is transplanted into another?
The pattern returns to normal in the form of the other animals rhythm
How does jet lag impact professional sports teams?
Teams with phase advance jet lag were more likely to lose, make mistakes, commit fouls, etc.
What does the suprachiasmatic nucleus (SCN) of the hypothalamus do in biological clocks?
It is the internal pacemaker that is the target of the retinohypothalamic tract
Examples of circadian rhythms
Body temp (lower at night), cortisol secretion (high in the morning), activity levels, and sleep/wakefulness
What do per and Tim inhibit?
Clock protein
What is always more active during light periods in nocturnal and diurnal animals?
SCN of the hypothalamus
What do melatonin signals do in seasonal rhythms?
Entrain circannual clock
When does phase delay happen?
Westward travel
Two types of jet lag
Phase advance and phase delay
What time are peak melatonin levels? What else is going on?
12-2am when per and Tim start to disintegrate
When is growth hormone release high and low?
High = stage 3 and 4 deep sleep Low = waking hours
Control morning activity and need light for entrainment
M cells
What backs up the fact that the SCN is a pacemaker?
Lesion studies, selective breeding, transplants, 24 and 20 hour hamsters
When does phase advance happen?
Eastward travel
What type of phase shift is fall back?
Phase delay. Analogous to westward travel
Humans our relationship to seasonal (circannual) rhythms
Equatorial animals, thus circadian rhythms dominate over circannual rhythms
The process of resetting the biological clock
Entrainment
What is shift maladaptation syndrome and who is it common in?
Sleep disorder caused by disruption of circadian rhythms and melatonin signaling. Common in people who work overnight shifts
An endogenous circannual clock, separate from the SCN but location unknown, runs at approximately 365 days
Seasonal rhythms
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GRAPHIC ON 8
When is temperature high and low?
High = waking hours Low = sleeping
How do cortisol levels change throughout the day?
Highest in the morning and drop throughout the day
How do circadian rhythms contribute to symptoms?
Some symptoms are worse at different times of the day
What do the ganglion cells in the retinohypothalamic tract not rely on and what do they contain?
They don’t rely on rods and cones and they contain the photopigment melanopsin (blue light)
Any rhythmic change that continues at close to a 24 hour cycle in the absence of 24 hour cues
Circadian rhythms
What releases melatonin?
Pineal gland
What do non-image receptor cells in the retinohypothalamic tract use?
Melanopsin
Larks vs owls
Larks = morning people Owls = night people
What is caffeine? What does it do postsynaptically?
Adenosine antagonist. Blocks adenosine receptors
Shift in activity in response to a synchronizing stimulus like light or dark
Phase shift
Where are the pineal gland and SCN?
In the pathway of the retinohypothalamic tract
What are some treatments for SAD?
Phototherapy and antidepressants (SSRIs)
What type of phase shift is spring forward?
Phase advance. Analogous to eastward travel
A type of depression that results from insufficient amounts of daylight during winter months
SAD
What question should physicians ask related to circadian rhythms?
What time is it and how can it be related to symptoms
What does free running cause?
Approximately 25 hour rhythm, sleep onset slightly later each day
When do levels of per and Tim start to decrease and why?
12-2am. Per and Tim disintegrate
What does the activation of clock trigger?
The production of per and tim
When do levels of per and Tim rise?
10:30 am - 12 pm
What is intrinsic rhythmicity?
Rhythmic in the absence of inputs/outputs
What does the night shift setting do?
Improves the ability to sleep by making screens show more red light
What does the retinohypothalamic tract contain and what does it do in biological clocks?
Contains non-image receptor cells that use melanopsin to carry light info
What two groups of circadian neurons are in the SCN?
M cells and E cells
When are the highest levels of per and Tim and what does it cause?
7-9pm. Causes new production of per and Tim to stop
What does the SCN of the hypothalamus follow?
Being rhythmic in the absence of inputs/outputs (intrinsic rhythmicity). Follows about same 25 hour rhythm when free running
Active during the daytime and sleep at night
Diurnal
What happens with light entrainment in amphibians and birds?
They have translucent skulls and photoreceptors in the brain and pineal gland receive light directly
When are the lowest levels of per and Tim and what do they activate?
Dawn (7-8am) and they activate clock
What does a lesion to the SCN cause?
Destroyed rhythm. No pattern
What types of cells are the ganglion cells in the retionhypothalamic tract?
Non-image forming
What areas are more at risk for SAD?
Far north and south
How can one system can throughout the day?
It can vary on many different levels
The hormone of darkness
Melatonin
Where is the SCN of the hypothalamus?
Above the optic chiam in the hypothalamus
What is the mammalian master biological clock that is the pacemaker of circadian rhythms?
Suprachiasmatic nucleus of the hypothalamus (SCN)
When is cortisol release high and low?
High = mornings and dropping throughout day Low = sleep
What can a circadian rhythm do to other rhythms?
It can set them
What does more exposure to light at night lead to?
A variety of negative effects
No environmental cues like light (constant exposure to light)
Free running
Inhibited clock activity, which decreases production of per and tim
High per and tim
How are alertness and temperature related?
They are positively correlated. They are high in waking hours and low in sleep
What can the disruption of circadian rhythms and melatonin signaling by unnatural zeitgebers cause?
Sleep disorders
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When are melatonin levels highest?
Sleep
What does melatonin do?
Opens the sleep gate but other systems must help us walk through it
What releases growth hormone and when?
Pituitary gland during stage 3 and 4 deep sleep
Control evening activity and need darkness for entrainment
E cells
Active at night and sleep during the daytime
Nocturnal
Is phase delay or phase advance easier to deal with and why?
Phase delay because it is easier to feel like you are going to bed later and waking up later than going to bed earlier and waking up earlier
What can be expressed within a single system?
Multiple rhythms
What does the pineal gland do in biological clocks?
Releases melatonin in the dark
What does the retinohypothalamic tract consist of?
Ganglion cells that project to the SCN
What causes SAD?
Overproduction of melatonin and lower levels of serotonin due to excessive reuptake
Example of a circadian rhythm setting other rhythms
Light info from photosensitive RGCs entrain the suprachiasmatic nucleus pacemaker. The pacemaker sets motor activity, eating, and body temp
What does clock promote?
Production of per and tim
What do high levels of per and Tim trigger and when?
They inhibit clock, resulting in decreased production of per and Tim. Around 3-430pm
Increased clock activity, which triggers production of per and tim
Low per and tim
What causes disruptions of circadian rhythms and melatonin signaling?
Unnatural zeitgebers like night shifts, jet lag, daylight savings time, cramming, and light pollution
What happens with light entrainment in mammals?
Light info goes from the eye to the SCN via retinohypothalamic pathway (starts in retina and goes to hypothalamus)
