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circadian
roughly 24h clock, found in nearly all living things
period (per)
on X chromosome in fruit flies. transcribed early in day (10pm), its protein (PER) is abundant 6 hrs later (4am)
represses transcription of per
TTFL
transcription-translation feedback loop, protein and its mRNA drive each others cycling
timeless (tim)
TIM binds to PER, and the PER/TIM dimer (levels high around 4 am) represses transcription of tim and per
clock (clk) and cycle (cyc)
codes for CLK and CYC, respectively. CLK-CYC dimer stimulates transcription of per and tim. PER/TIMblocks CLK-CYC binding to DNA thus repressing transcription
doubletime (dbt)
codes for DBT, binds to PER causing it to breakdown so levels of PER rise slower than usual. results in 24h cycle
mammalian homologs
cryptochrome (cry) codes for CRY which bind to PER to form dimer
clk=clk
cyc=bmal1
dbt=ck1ε
zeitgeber
german for “time giver”. all cues keeping cellular clocks in sync (e.g. light, temp, food, etc)
main zeitgeber
light. sensed by melanopsin retinal ganglion cells, which project to the suprachiasmatic nucleus (SCN) of the hypothalamus.
suprachiasmatic nucleus
SCN. the master clock, sits right above the optic chiasm csq(where ½ the fibres in the optic nerve cross to the other side of the brain)
resetting clocks
signals from retinal ganglion cells cause chemical changes in SCN cells, leading to a breakdown of PER/CRY
if levels were already falling, this speeds it up, ie setting clock slightly forward
if levels were rising, this counteracts, ie sets the clock back.
entrainment
neural signals pass to other brain areas adjusting intracellular clocks throughout the body. nudging a clock into synchrony with another rhythym. (SCN is entrained to night and day, other clocks entrained to SCN)
Pineal body
in the diencephalon, secretes melatonin which resets master clocm (SCN) towards nighttime
chronotypes
within one species people sleep at different times, thought to evolve for the “safety of the herd”
orexin
released by LH, causes arousal. deficiency causes narcolepsy. inhibits MCH
lateral hypothalamus cells
active in darkness, releasing the neuropeptide melanin-concentrating hormone (MCH) inducing sleep. inhibts orexin
sleep pressure
buildup of adenosine causes sleepiness. caffeine blocks adenosine receptors
rapid eye movement (REM) sleep
eyes move, dream, erratic 30-40 Hz brain waves.
muscle tine vanishes
aquatic animals
dont have REM sleep (ie dont dream) because loss of muscle tone would cause drowning
non-REM (nREM) sleep
dreamless, with slower brain waves. 3 numbered stages, with three being the deepest sleep (2-4Hz brain waves)
sleep stages cycle
The first REM stage occurs after about 90 minutes. As the night
progresses, sleep gets shallower and REM stages longer, and you
may wake up occasionally
why do we need sleep
sleep deprivation can cause problems with cognitive function, learning, and memory.
post sleep deprivation
you catch up on nREM first, then next few nights wil start to have REM sleep as normal
