Sleep Science and Habits

98 flashcards by MentisLibrary

What sleep is and how to sleep better, grounded in the research: circadian timing and light, sleep pressure and caffeine, the sleep stages, what sleep restriction does, naps and shift work, and the disorders that need a clinician.

What are the two processes in the two-process model of sleep regulation?
Process S, the homeostatic sleep pressure that builds the longer you are awake, and Process C, the circadian rhythm that sets when you are biologically ready to sleep.
What is homeostatic sleep pressure?
The rising drive to sleep that accumulates across waking hours and dissipates during sleep.
What role does adenosine play in sleepiness?
Adenosine accumulates in the brain during wakefulness and promotes sleep, and levels fall during sleep.
How does caffeine work?
It blocks adenosine receptors, so the accumulated sleep pressure is still there but you feel it less.
What is the approximate half-life of caffeine in adults?
Around 5 hours on average, with a wide individual range of roughly 3 to 7 hours, and longer in pregnancy or with some medications.
Where is the body's master circadian clock?
In the suprachiasmatic nucleus, a small paired structure in the hypothalamus above the optic chiasm.
How long is the intrinsic human circadian period?
Slightly longer than 24 hours on average, close to 24.2 hours when measured under controlled laboratory conditions.
What is a zeitgeber?
An external time cue that entrains the body clock. Light is by far the strongest, with meals, exercise and social schedules playing smaller roles.
Which cells in the eye signal light to the body clock?
Intrinsically photosensitive retinal ganglion cells, which contain the pigment melanopsin and are most sensitive to short-wavelength blue light.
What is a phase response curve for light?
A map of how light at different biological times shifts the clock. Light in the evening and early night delays the clock, and light in the late night and early morning advances it.
What is dim light melatonin onset?
The rise in melatonin measured under dim light conditions, typically starting about 2 hours before habitual sleep onset. It is the standard laboratory marker of circadian phase.
When does core body temperature reach its daily minimum?
Roughly 2 to 3 hours before habitual wake time, near the end of the biological night.
What does melatonin actually do?
It is a hormone released by the pineal gland in darkness that signals biological night to the body and helps time sleep.
What does the evidence say about melatonin supplements?
Small doses taken at the right time can shift circadian phase and help with jet lag and delayed sleep phase. Effects on sleep quality in ordinary insomnia are modest.
What is a chronotype?
An individual's natural tendency toward earlier or later sleep and activity timing, partly genetic and changing across the lifespan.
How does chronotype change with age?
Children tend to be early types, timing shifts markedly later during adolescence and peaks in the late teens, then gradually moves earlier again through adulthood.
What is social jet lag?
The mismatch between the sleep timing your clock wants and the timing your work or school schedule imposes, measured as the difference in mid-sleep between free days and work days.
What are the stages of sleep in current scoring?
Three non-REM stages, N1, N2 and N3, plus REM sleep.
What happens during N1 sleep?
The light transition from wakefulness into sleep, lasting a few minutes, with slow rolling eye movements and easy arousal.
What characterizes N2 sleep?
The most abundant stage, marked by sleep spindles and K-complexes on the EEG, occupying roughly half of adult sleep.
What is a sleep spindle?
A short burst of rhythmic brain activity around 11 to 16 hertz that appears in N2 sleep.
What is N3 or slow wave sleep?
The deepest non-REM sleep, dominated by large slow delta waves, hardest to wake from, and concentrated in the first third of the night.
What defines REM sleep?
Rapid eye movements, an active brain pattern resembling wakefulness, near-total loss of skeletal muscle tone, and most vivid dreaming.
Why does the body paralyze the muscles during REM sleep?
Descending inhibition of motor neurons prevents the body from acting out dream content.
How long is a typical sleep cycle?
About 90 minutes on average, with a normal range of roughly 70 to 120 minutes, giving four to six cycles a night.
How does sleep composition change across the night?
Deep N3 sleep dominates the early cycles, while REM periods lengthen and cluster in the final hours before waking.
What is sleep onset latency?
The time from lights out to falling asleep. Around 10 to 20 minutes is typical for a healthy adult.
What is sleep efficiency?
The proportion of time in bed actually spent asleep. Around 85 percent or higher is generally considered normal.
What does WASO mean?
Wake after sleep onset, the total time spent awake between first falling asleep and finally getting up.
What is polysomnography?
An overnight laboratory sleep study recording brain activity, eye movements, muscle tone, breathing, oxygen levels and heart rhythm.