Stages of Sleep

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Sleep: A beautiful, complex and essential life process.

(NB: Must Draw Relevant Diagrams- Sleep EEG and Sleep Cycle graph- from your standard textbooks)

(NB: On smartphones best read in landscape mode)

  • Definition- Sleep is the state of unconsciousness from which the individual can be aroused by sensory or other stimuli. It is a recurring phenomenon during which eyes are closed, muscles are relaxed, and the nervous system is relatively inactive.
  • Types-
    • NREM- Non-Rapid Eye Movement
    • REM- Rapid Eye Movement
    • The average duration of each sleep cycle is 90 minutes, with 5 minutes of REM sleep alternating with 85 minutes of NREM
  • NREM-
    • Major Part of Sleep(80%)
    • Slow Wave Sleep
    • Eyes show slow rolling movement.
    • Heart rate, respiratory rate, blood pressure are decreased
    • Pulsatile secretion of growth hormones and gonadotropins
    • Dreams from this stage cannot be recalled.
    • Has 4 stages-
      • Stage 1-
        • Theta Waves, A waves
        • Deep sleep
        • Low voltage
    • Stage 2-
      • Sleep spindle
      • High Voltage Biphasic K-complex
    • Stage 3:-
      • Delta waves
      • Stronger sleep
    • Stage 4
      • Dome like very slow delta waves
      • Deep sleep
      • Marked synchronisation
      • Rolling movement of eyes stop with eyes turned upwards
  • REM-
    • Small part of sleep(20%)
    • Fast Wave Sleep
    • Heart Rate, Respiratory Rate, Breathing Rate are irregular.
    • Reduced Muscle tone
    • Beta waves are observed showing that the brain is active
    • Oxygen consumption by brain is high
    • Twitches, penile erection, and bruxism(teeth grinding) are also seen in this phase of sleep.
    • It is difficult to wake a person from REM sleep, but once awake he is fully alert.
    • Include bar graph of sleep cycles
  • Genesis of NREM Sleep-
    • Low Frequency Stimulation(8Hz) of-
      • Sleep facilitatory Centre present in anterior hypothalamus
      • Medullary Synchronising zone
    • Low as well as high frequency stimulation of Pre-Optic Area and diagonal band of Broca in the Basal Forebrain Sleep zone.
    • Stimulation of GABAergic inhibitory neurons
    • Inhibition of RPO nucleus(Reticularis Pontis Oralis)
    • Orexins enhance GABAergic activity
  • Genesis of REM Sleep-
    • Activity of cholinergic neurons of midbrain which produces PGO spikes (Ponto-Geniculo-Occipital).
    • Stimulation of RPO nucleus (waking on cells)
  • Importance of Sleep-
    • Period of Body’s rest and metabolic restoration
    • Learning and memory
    • Mental well being
    • Role in homeostasis
    • General physical growth and reproductive maturity in children
  • Sleep Disorders-
    • Narcolepsy- Irresistible urge to fall asleep.
    • Cataplexy- loss of muscle tone, person falls to ground
    • Insomnia- insufficient sleep
    • Fatal familial insomnia
    • Somnambulism
    • Nocturnal enuresis (bed wetting)
    • Night terrors
    • Sleep Apnoea
    • Restless leg syndrome