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Overview

Snapshot
  • A 19-year-old female presents with chronic fatigue. She reports feeling very sleepy throughout the day, has been told that she would doze off, and then eventually drop her head on to the desk. She notes periods of not being able to move after waking up and fell to the ground after being excited at the news of her sister’s pregnancy. What frightened her the most are the vivid “visions” she would get when she is about to fall asleep.  
Sleep Stages
 
Sleep Stage 
Description EEG Waveform
 
  • Awake and alert
  • Beta
 
  • Awake and eyes closed
  • Alpha
Stage N1
  • Light sleep
  • Theta
Stage N2
  • Deeper sleep
  • Sleep spindles and K complexes
Stage N3
  • Deepest non-REM sleep
  • Sleepwalking
  • Night terrors
  • Bedwetting
  • Delta 
REM
  • Dreaming
  • Beta
  • Suprachiasmastic nucleus of the hypothalamus is involved in circadian rhythm regulation
  • GABA agonists (alcohol, benzodiazepines, and barbiturates) reduce REM and delta sleep
REM Sleep
  • Description
    • dreaming
    • loss of motor tone
    • may serve a memory processing function
  • Physiology
    • same EEG pattern as when awake
      • therefore called "paradoxical sleep" or "desynchronized sleep"
    • rapid eye movement
      • defining feature of REM sleep
      • due to activity of paramedian pontine reticular formation
    • erection
    • ↑ and variable pulse and blood pressure
    • loss of muscle tone
  • Neurotransmitters
    • acetylcholine is the principle neurotransmitter
    • norepinephrine, serotonin, and histamine suppress REM sleep
      • therefore, certain antidepressants (eg, SSRI, SNRI) can pharmacologically suppress REM sleep
  • Timing
    • occurs every 90 min
    • duration ↑ with every cycle
    • amount of REM sleep ↓ with age
Sleep Disorders
  • Narcolepsy  
    • disordered regulation of sleep cycles secondary to loss of orexin (hypocretin) neuropeptides
    • excessive daytime sleepiness
    • sleep paralysis
    • may include hallucinations
      • hypnagogic
        • just before sleep
      • hypnopompic
        • just before awakening
    • nocturnal and narcoleptic sleep episodes start off with REM sleep
    • cataplexy
      • loss of all muscle tone following a strong emotional stimulus
      • only some patients
      • patients have undetectable hypocretin-1 in levels in CSF 
    • stong genetic component
    • treat with stimulants 
      • e.g., modafinil (first-line) and amphetamines (generally second-line)
  • Sleep apnea
    • see Sleep Apnea
 

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