Physiology of Sleep Flashcards
What is the overall definition of sleep? Neuroscience definition?
temporary state of unconsciousness from which one can awaken when stimulated
Neuro: dynamic state of shifting electrical activity & flow of chemicals
What is a sleep study?
polysonnography
EEG: electroencephalogram
EMG: electromyogram
EOG: electrooculogram
What are the stages of a sleep cycle? How long are each cycle? How many sleep cycles does a typical adult have / night?
A. Non-Rapid Eye Movement sleep (75%)
B: Rapid Eye Movement sleep (25%)
whole cycle ~90 minutes & have ~5 cycles /night
What is the trend for percentage of time spent in the different phases of the sleep cycle as we age?
babies → ~ 85% REM
adults → ~25% REM
% time spent in REM decreases as we age
What are the 5 basic steps to the sleep cycle?
- Awake
- N1: transition
- N2: light sleep
- N3: deep sleep
- REM sleep
notice that in the beginning, the length of time spent in N3 is the largest & the length of time spent in REM increases toward the end
The first half of sleep is considered what type of sleep?
The second half is considered what type of sleep?
First half: deep sleep
Second half: REM sleep
What types of waves are seen seen in each stage of sleep?
- Awake (alert) : Beta
- Awake (relaxed) : alpha
- N1 (drowsiness) : theta
- N2 (light sleep): theta
- N3 (deep sleep) : delta
- REM : Beta
What neurotransmitters are responsible for the different waves seen in different levels of sleep?
- Awake (eyes open) : Beta → increased norepinephrine
- Awake (eyes closed) : alpha → increased histamine
- N1, N2, N3 : theta & delta → increased GABA
- REM : beta → increased GABA + ACh
What are the characteristics of REM sleep?
saw-tooth wave & PGO activity
Fill out the trends indicated by the black bocks in the provided table:
What is the sleep center of the brain & what is the main “switch”?
hypothalamus
Ventrolateral preoptic nucleus (VLPO)
What is the mechanism of sleep induction by adenosine?
- Adenosine binds to the A1 & A2 receptors on the VLPO of the hypothalamus
- this activates the VLPO → secretes GABA → promotes sleep
How does caffeine inhibit sleep?
Caffeine binds to & blocks the A1 & A2 receptors on the VLPO
VLPO is inhibited from producing GABA
Why do we build up adenosine during the day?
ATP use
Increased levels of what substance in the forebrain promotes sleep?
adenosine
What are the nuclei in the hypothalamus that are related to sleep & wakefulness? Actions of each?
- VLPO → GABA secretion (induce sleepiness)
-
SCN → stimulated by light (help you wake up)
- during sleep, produces melatonin (keep you asleep)
- Lateral Hypothalamus → orexin (keep you awake)
Lesion in the lateral hypothalamus can lead to what condition?
narcolepsy
d/t loss of orexin neurons
What are the orexinergic neuronal functions? What conditions can happen if there is something wrong with its function
maintain proper vigilance
Wrong: narcolepsy, cataplexy, primary hyprsomnia
What are the GABAergic neuronal functions?
go to bed
axons from VLPO project to major nuclei to inhibit primary arousal centers
What are the primary arousal centers?
TMN, LH, PPT/LDT, RN, LC
What stages are “quiet sleep”? What are the characteristics of this sleep?
NREM (N1, N2, N3)
slows down brain activity, heartbeat, respiration, & body temp
What stages are “slow wave sleep”? What are the characteristics of this sleep?
NREM sleep
low brain activity = low frequency EEG waves
What important things happen during N3?
takes care of fatigue: brain glycogen & ATP are replenished
tissue repair, GH & prolactin secretion
What are the characteristics of N1-NREM stage?
- ~5% total sleep
- altered state of consciousness (drowsiness)
- decreased HR, respiration, body temp + relaxed muscles
- EEG: mixed frequency (alpha & theta)
Hypnic jerks & Hypnagogic hallucinations
What are the characteristics of N2-NREM stage?
- ~45% sleep
- light sleep - theta waves
- consolidates motor learning
- Bruxism: pathological teeth grinding happens at this stage
What are the EEG characteristics of N2 sleep?
-
sleep spindles
- bursts of high frequency waves - sleep through loud noises
-
K-complexes
- high amplitude single wave - suppress cortical arousal & keep you asleep
What are the characteristics of N3-NREM stage?
- ~25% total sleep
- glycogen replenishment & tissue repair
- GH secretion
- _glymphatic clearanc_e - unique waste clearance system in brain
- Deep/restful sleep
- muscles relax & vital signs decrease
- hard to wake up → groggy, impaired mental status (sleep inertia)
What are the EEG characteristics of N3 sleep?
- delta waves (slow wave sleep)
What stage of sleep is crucial for declarative memory (ie. facts)?
N3
Patients with depression get very little of what stage of sleep?
N3
What stages do sleep-walking, bed-wetting & night terrors occur?
N3
Snoring occurs in which stage?
can occur in all stages, but most frequently N3
What are the characteristics of REM stage?
- ~25% total sleep
- Rapid Eye Movements (EOG)
- muscle atonia (EMG)
- dreams (EEG)
- increase in brain activity & O2 use
- irregular heart & breathing rates
- parasympathetic nervous system activation
- constriction of pupil, erection
What phase of sleep is crucial for procedural memory?
REM
What are the EEG characteristics of REM sleep?
beta waves with dominant “PGO activity” = bursts of “sawtooth” wave
- P : ponto
- G : genicular
- O : occipital
Why is REM sleep also called paradoxical sleep?
increase in brain activity & increase in oxygen use
long, vivid dreams → similar to wakefulness
“shallow stage of sleep”
Why do heart attacks often occur in early morning?
the fluctuations seen in heart rate & breathing rate during REM sleep
What is happening when some people “act out their dreams”?
- REM sleep w/o atonia
- d/t loss of REM atonic neurons in pons
Nightmares occur during what time of sleep? What are the characteristics of nightmares?
REM during the later part of the night
can occur in any age, associated with mild physiological changes & you remember the event
What is Process H?
promotion of sleep
accumulation fo “sleep factors” ie. adenosine
What is Process C?
circadian rhythm
absence of light decreases alertness - SCN + pineal gland
What cardiovascular changes do you see during sleep?
- decrease
- BP
- HR
- CO
- vasomotor tone
- plasma volume
What respiratory changes do you see during sleep?
- decrease
- force
- rate
- CO2 sensitivity
- pulmonary ventilation
What muscular changes do you see during sleep?
- decrease
- muscle tone
- increase
- repair
What urinary changes do you see during sleep?
- decrease
- urine formation
- increase
- phosphate content
- specific gravity
What digestive changes do you see during sleep?
relaxed esophageal sphincter
What nervous system changes do you see during sleep?
- decrease
- reflexes
- sensation
What secretion changes do you see during sleep?
- decrease
- salivary & lacrimal
- ghrelin
- BMR
- increase
- sweat & gastric
- leptin
