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Physiology of sleep and E.E.G for undergraduates


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Physiology of Sleep and EEG

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Physiology of sleep and E.E.G for undergraduates

  1. 1. PHYSIOLOGY OF SLEEP AND EEG Dr. Mohamed Abdelghani M.B.B.Ch., M.Sc., M.D. Psych.
  2. 2. OBJECTIVES:  By the end of this lecture, you should understand: 1) Difference between sleep & coma. 2) Why do we sleep? 3) Mechanism of sleep. 4) EEG waves 5) Types and Stages of sleep: (NREM & REM). 6) Sleep/awake cycle. 7) Sleep disorders. 8) Sleep Hygiene.
  3. 3. DEFINITIONS  Sleep:  A state of loss of consciousness from which a subject can be aroused by appropriate stimuli.  Coma:  A state of unconsciousness from which a subject cannot be aroused.
  4. 4. WHY DO WE SLEEP? “FUNCTIONS OF SLEEP”: 1) Restoration or repair:  Waking  Sleep 2) 3) 4) 5) 6) life disrupts homeostasis may conserve some energy Protection with the circadian cycle. Circadian synthesis of hormones. Consolidation of learning. Remodelling of synaptic function. Dreaming.
  6. 6. WHAT MAKES US FALL ASLEEP? The old theory of sleep “The passive process”: I.  Discharging of RAS neurons for many hours of wakefulness  Fatigue of RAS neurons  Sleep . The new theory of sleep “The active sleep- II. inducing inhibitory process”:  Different mediators actively inhibit the RAS  sleep: 1. Serotonin-secreting Raphe fibers inhibit the RAS  sleep. 2. Melatonin “hormone secreted by the Pineal Gland” during darkness  inhibits RAS  sleep .
  7. 7. EEG WAVES
  8. 8.  The frequencies of brain waves range from 0.5-500 Hz.  The most clinically relevant waves: 1) Alpha waves - 8-13 Hz 2) Beta waves - Greater than 13 Hz (18-30) 3) Theta waves - 3.5-7.5 Hz 4) Delta waves - 3 Hz or less
  9. 9. 1) ALPHA WAVES  Seen in all age groups but are most common in adults.  Most marked in the parieto-occipital area.  Occur rhythmically on both sides of the head but are often slightly higher in amplitude on the nondominant side, especially in right-handed individuals   Occur with closed eyes , relaxation, wondering mind. Disappear normally with attention (eg, mental arithmetic, stress, opening eyes, any form of sensory stimulation), then become replaced with irregular low voltage activity.
  10. 10. 2) BETA WAVES Seen in all age groups.  Small in amplitude , usually symmetric and more evident anteriorly.  Drugs, such as barbiturates and benzodiazepines, augment beta waves.  > 13 Hz/sec 
  11. 11. 3) THETA WAVES Normally seen during sleep at any age.  In awake adults, these waves are abnormal if they occur in excess.  Theta and delta waves are known collectively as slow waves. 
  12. 12. 4) DELTA WAVES Slow waves, have a frequency of ≤ 3Hz or less.  Normally seen in deep sleep in adults as well as in infants and children.  Delta waves are abnormal in the awake adult.  Often, have the largest amplitude of all waves.  Delta waves can be focal (local pathology) or diffuse (generalized dysfunction). 
  13. 13. SLEEP SPINDLES Groups of waves that occur during many sleep stages but especially in stage 2.  Have frequencies in the upper levels of alpha or lower levels of beta.  Lasting for a second or less, they increase in amplitude initially and then decrease slowly. The waveform resembles a spindle.  They usually are symmetric and are most obvious in the parasagittal regions. 
  15. 15. TYPES OF SLEEP “DEPENDING ON EEG CRITERIA” Slow-wave sleep (non-REM): 1.   Stage 2 NREM  Stage 3 NREM  2. Stage 1 NREM Stage 4 NREM Rapid Eye Movement Sleep (REM):
  17. 17. DISTRIBUTION OF SLEEP STAGES  While NREM occupies about 75-80%, it is interrupted by intervening REM sleep period.  In a typical night of sleep, a young adult: I. II.  First enters NREM sleep, passes through stages 1 , 2 , 3 and 4. Then goes into the first REM sleep episode. This cycle is repeated at intervals of about 90 minutes throughout the 8 hours of a night sleep.  Therefore, there are 4-6 sleep cycles per night (and 4-6 REM periods per night).  As the night goes on  there is progressive reduction in stages 3 and 4 sleep and a progressive increase in REM sleep .
  18. 18. Physiological Changes During NREM and REM Sleep Physiological Process NREM Brain activity Decreases from wakefulness Heart rate Slows from wakefulness Blood pressure Decreases from wakefulness Sympathetic nerve activity Decreases from wakefulness Muscle tone Similar to wakefulness Blood flow to brain Decreases from wakefulness Respiration Decreases from wakefulness Airway resistance Increases from wakefulness Body temperature Sexual arousal Is regulated at lower set point than wakefulness; shivering initiated at lower temperature than during wakefulness Occurs infrequently REM Increases in motor and sensory areas, while other areas are similar to NREM Increases and varies compared to NREM Increases (up to 30 percent) and varies from NREM Increases significantly from wakefulness Absent Increases from NREM, depending on brain region Increases and varies from NREM, but may show brief stoppages; coughing suppressed Increases and varies from wakefulness Is not regulated; no shivering or sweating; temperature drifts toward that of the local environment Greater than NREM
  20. 20. • Periods of sleep and wakefulness alternate about once a day. • A circadian rhythm consists typically of 8h sleep and 16h awake. • This rhythm is controlled by 1) The suprachiasmatic (SCN) nucleus “The Biological clock”: located in in the hypothalamus. 2) Melatonin release “from the Pineal Body”.
  22. 22. SLEEP DISORDERS ARE DIVIDED IN 2 SUB-TYPES I. Dyssomnias: Sleep disorders that are characterised by disturbances in the amount, quality or timing of sleep.  E.g.:  Insomnia  Hypersomnia  Sleep apnea  II. Parasomnias:   Dysfunctions or episodic events occurring with sleep. E.g.: Sleep-walking (somnambulism)  Sleep-related enuresis (bedwetting)  Sleep-talking (somniloquy)  Sleep-terrors and nightmares 
  23. 23. Sleep Hygiene 1. Regular, daily physical exercises (preferably not in the evening). 2. Minimize daytime napping. 3. Avoid fluid intake and heavy meals just before bed-time. 4. Avoid caffeine intake (e.g. tea, coffee, cola drinks) before sleeping hours. 5. Avoid regular use of alcohol (especially avoid use of alcohol as a hypnotic for promoting sleep). 6. Avoid reading or watching television while in bed. 7. Sleep in a dark, quiet, and comfortable environment. 8. Regular times for going to sleep and waking-up. 9. Try relaxation techniques.