Snapshot A 19-year-old woman 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 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 REM sleep within 15 minutes of sleep onset treatments stimulants e.g., modafinil (first-line) and amphetamines (generally second-line) cataplexy serotonin and dopamine reuptake inhibitor Sleep apnea see Sleep Apnea