Sleep and Circadian Rhythm Flashcards
How does wakefulness differ from REM and non-REM sleep?
Wakefulness:
- aware, active cortex
REM:
- unconscious, active cortex
- skeletal muscle paralysis
Non-REM:
- unconscious, reduced cortical activity
- reduced muscle tone
What are the components of polysomnography?
1) Electroencephalogram (EEG)
- brain wave activity
2) Electro-oculogram (EOG)
- eye movements
3) Electromyogram (EMG)
- muscle tone
What is the main indication for a clinical sleep study?
Sleep apnea (obstructive)
- additional bio-signals collected:
(airflow sensors, oximetry, nasal pressure, esophageal pressure, body position, respiratory effort, ECG)
How do the different sleep stages differ?
Wake with eyes closed:
- α wave predominance
- tonic EMG
N1:
- low voltage theta activity
- slow eye movements
- reduced tone EMG
N2:
- K complexes (high amp, negative wave, followed by slower positive wave) + sleep spindles (12-15Hz bursts >0.5sec)
- no eye movements
- reduced tone EMG
N3: slow wave sleep
- high amp delta activity
- no eyemovements
- reduced tone EMG
REM:
- low voltage mixed freq. waves
- rapid eye movements
Of the sleep stages, ___________ is more prominent in the first half of the night, while _______ is more prominent in the latter.
1st 1/2: N3 Slow wave sleep
2nd 1/2: REM
How long is 1 REM cycle?
90-120mins
- but varies between and within individuals
How does our sleep structure change with age?
Infants have more frequent REM cycles + REM4 (deeper sleep) than older individuals
What are the 2 major sleep-promoting processes?
1) Homeostatic sleep drive
- builds with time spent awake
2) Circadian sleep drive
- ↑ during nighttime hours
What is an example of a somnogen?
Adenosine
What are 3 ways adenosine promotes sleep?
1) Adenosine builds up when energy is used and ATP consumes
2) Excess adenosine non-synaptically released by facilitated transport
- extracellular adenosine is an indicatory of neuronal energy stores
3) Adenosine levels ↑ when awake and ↓ when sleeping in basal forebrain
What are 3 neurotransmitters in the arousal system?
1) ACh
- pedunculopontine, dorsolateral tegmental nuclei, basal forebrain
2) NA
- locus coeruleus
3) Serotonin
- raphe nuclei
4) Dopamine
- ventral tegmental area
5) Histamine
- tuberomammillary nucleus
6) Orexin
- lateral hypothalamus
How does the ventrolateral preoptic nucleus promote sleep?
GABAergic → inhibit arousal system
- activated by prostaglandin D2 (somnogen)
Which type of neurons are active during REM sleep?
1) GABA (inhibit arousal)
2) ACh (cortical activity)
Which chemical stabilises sleep-wake transition?
Orexin
- activated arousal system
- inhibited by VLPO (GABA)
How do the sleep cycles of narcolepsy differ from normal individual?
1) More sleep-wake transitions vs normal subject
2) Direct entry into REM sleep from wakefulness (skip N1-3)
3) Multiple sleep bouts/attacks during daytime
Which part of the brain controls the circadian rhythm?
Suprachiasmatic nucleus
What is the physiology of blue light therapy in treating circadian misalignment?
Blue-light sensitive melanopsin in retinal ganglion cells → SCN → light induced resetting of circadian rhythm
What are the 2 chronotypes?
1) Morningness
- shorter-than-average circadian period
2) Eveningness
- longer-than-average circadian period
What is insomnia?
difficulty falling asleep or maintaining sleep across the night
What is obstructive sleep apnea?
excessive daytime sleepiness due to repeated obstruction of the airway during sleep
- fragmented sleep and ↓ slow-wave sleep
- During sleep, muscle tone is reduced including the upper motor airway
Obstructive sleep apnea
- causes (1)
- indicator (1)
- sequelae (3)
Causes: obesity
Indicator: chronic snoring
Sequelae:
- Hypoxemia
- HTN
- IHD
- excessive daytime sleepiness
What are 2 movement disorders of sleep?
1) Periodic limb movement disorder
- excessive leg movements during sleep
- can wake person
2) Restless legs syndrome
- uncomfortable sensations in legs relieved by stretch/rubbing
- Diagnostic criteria:
1) Urges to move the legs, accompanied or caused by uncomfortable and unpleasant sensations in the legs
2) a worsening of symptoms during periods of rest or inactivity
3) the unpleasant sensations are partially or totally relieved by movement (e.g., walking or stretching)
4) the symptoms are worse in the evening or at night compared to the daytime.
What is cataplexy?
Sudden loss of muscle tone while awake, often caused by emotion
- symptom of narcolepsy
What are 4 symptoms of narcolepsy?
1) excessive daytime sleepiness
2) cataplexy
3) sleep paralysis
4) hypnagogic hallucinations
What is 1 cause of narcolepsy?
Loss of orexin neurons
What is delayed sleep-wake phase disorder?
Sleep onset insomnia and extreme difficulty waking in the morning
