anatomy

Sleep 101: Brain Activity and Sleep Disorders, Sleep Apnea, Circadium Rhythms, and How to Sleep Better at Night

Sleep and Brain Activity Sleep disorders affect up to 70 million people and cost around $15.9 billion annually

  1. Brain Activity During Sleep
    1. Experiments using EEG
  • EEG stands for electroencephalography, which was used to examine human brain waves in the 1950s
  • RESULTS: 
    • during first hour of sleep brain waves slow down gradually
      • accompanied by relaxation of muscles and eyes
      • heart rate, blood pressure and body temp. fall
      • if woken, people recall only fragmented thoughts
    • over next half hour brain goes from deep slow wave sleep to REM (rapid eye movement) sleep which is characterized by neocortical EEG waves similar to those observed during waking
      • accompanied by ATONIA, paralysis of body’s muscles (only ones that allow breathing and control eye movements remain active)
      • active dreaming occurs
      • variable heart rate, blood pressure, body temp.
    • overnight, slow wave and REM sleep cycles alternate with slow wave sleep becoming less deep and REM periods more prolonged until person wakes up

Sleep Disorders: Insomnia, OSA, Apnea, Narcolepsy

  1. Sleep Disorders
    1. Insomnia
  • most common sleep disorder
  • some insomniacs have trouble falling asleep initially but others sleep then wake up partway through the night and can’t fall asleep again
  • sedatives/drugs can help but none produce natural and restful sleep state
  1. Other Common Disorders
  • Excessive daytime sleepiness, has many causes like self-imposed sleep deprivation
  • Obstructive sleep apnea in which individual has difficulty breathing and wakes without entering deeper stages of sleep
    • causes high blood pressure and may increase risk of heart attack
    • increased daytime sleepiness resulting from sleep apnea can lead to increased risk of daytime accidents
    • treatment can include variety of strategies to reduce airway collapse like using device to induce continuous positive airway pressure that keeps it open; some cases surgery is needed
  • Periodic limb movements of sleep are intermittent leg/arm jerks that occur as individual enters slow wave sleep
    • cause arousal from sleep
    • related disorder, REM behavior disorder, occurs when muscles fail to become paralyzed during REM sleep —> people act out dreams by getting up and moving around 
    • both disorders common in people with Parkinson’s disease and can be treated with drugs used for those with Parkinson’s OR with a benzodiazepine called clonazepam
  • Narcolepsy is uncommon condition in which switching mechanisms controlling transitions into sleep (particularly REM sleep) do not work properly
    • caused by loss of nerve cells in lateral hypothalamus that contain neurotransmitter orexin (a.k.a hypocretin)
    • people with narcolepsy have sleep attacks during day (suddenly fall asleep)
    • people with condition tend to enter REM sleep very quickly and may enter dreaming state when partially awake, condition known as hypnagogic hallucination
    • people with narcoleptics also have attacks during which lose muscle tone, attacks known as cataplexy, which can be triggered by emotional experiences

Regulation of Sleep

  1. How Is Sleep Regulated?
  • wakefulness maintained by several brain systems — mostly located in upper brainstem — where nerve cells connect with forebrain
    • nerve cells containing orexin, in hypothalamus, are important in wakefulness
    • hypothalamic nerve cells containing histamine are important as well
    • activation of thalamus and basal forebrain by acetylcholine is important in maintaining activity in cerebral cortex and consciousness —> reflected in activated, low-voltage EEG
  • during non-REM sleep arousing systems become much less active and transmission of info from senses through thalamus is curtailed —> first stage of sleep
  • REM sleep characterized by internally activated brain and activated EEG, but with external input suppressed
    • neurons in brainstem cause signal forebrain, which becomes excited and leads to rapid eye movements and muscle suppression
    • in abscence of this external input, forebrain excitation drives vivid dreams
    • REM sleep believed to occur every 90 minutes because of on-off switching of REM-generating neurons

Sleep-Wakefulness Cycle: Circadium Rhythm and Homeostatic System

  1. The Sleep-Wakefulness Cycle
    1. Determining Factors
  • Circadian system — time of day or night and how long we have been awake
    • regulated by suprachiasmatic nucleus, a small group of nerve cells in hypothalamus
      • cells express clock proteins, which go through biochemical cycle of around 24 hours
      • receives input directly from retina and “clock” can be reset by light so remains linked to outside day-night cycle
      • provides signals to subparaventricular nucleus in brain, which contacts dorsomedial nucleus of hypothalamus —> dorsomedial nucleus in touch with ventrolateral preoptic nucleus and orexin neurons in lateral hypothalamus which directly regulate sleep and arousal
    • Orexin
      • provides excitatory signal to arousal system, esp. norepinephrine neurons
      • orexin activation helps prevent abnormal transitions into REM sleep during day
  • Homeostatic system — responds to progressively longer wake periods by increasing urge to sleep
    • longer a person is awake, greater the chance of increase in sleep-inducing factor(s)
    • adenosine is neurochemical believed to be important sleep factor; with longer waking time increased levels of adenosine present
    • ATP, adenosine triphosphate, also increases during sleep (produced during sleep) —> supports notion that sleep necessary for providing restorative energy b/c ATP powers nerve cells in brain

How to Sleep Better at Night

  1. Reduce long daytime naps
  2. Decrease light exposure at night before bedtime
  3. Reduce caffeine intake close to bedtime
  4. Relax near the evening time
  5. Take a relaxing shower or bath before bedtime

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