Sleep - Physiology Lecture SlideshowSleep - Physiology Lecture Slideshow


  • 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


During each night, a person goes through stages of two types of sleep
that alternate with each other.

(1) Slow-wave sleep, in which the brain waves are strong and of low
frequency and

(2) Rapid eye movement sleep (REM sleep), in which the eyes undergo
rapid movements despite the fact that the person is still asleep.

  • Most sleep during each night is of the slow-wave variety(deep, restful
    sleep) that the person experiences during the first hour of sleep after
    having been awake for many hours.
  • REM sleep, on the other hand, occurs in episodes that occupy about
    25 percent of the sleep time in young adults; each episode normally
    recurs about every 90 minutes for 5 to 30 minutes. This type of sleep
    is not so restful.
  • When the person is extremely sleepy, each bout of REM sleep is short and may even be
  • Conversely, as the person becomes more rested through the night, the durations of the
    REM bouts increase.

Basic Theories Of Sleep

Passive Theory Of Sleep:

  • An earlier theory of sleep was that the excitatory areas of the upper
    brain stem, the reticular activating system, simply fatigued during the
    waking day and became inactive as a result.
    Active inhibitory theory of sleep:
  • A center located below the mid-pon level of the brain stem appears
    to be required to cause sleep by inhibiting other parts of the brain.

Neuronal Centers Involved In Sleep:

Stimulation of these neuronal centers cause sleep:

  1. Raphe nuclei in the lower half of pons and in medulla.
  2. Nucleus of tractus solitaries.
  3. Suprachiasmatic area of hypothalamus & diffuse nuclei of
In posterior horn, where the inhibt the incoming pain signals.
::Sensory signal from GP and vagus to NTS in medulla and pons.NTS INHIBIT RAS.
maintaining regular sleep patterns via circadian rhythms, though this is mostly based on the presence of light or dark sensory cues.

Neurotransmitter Substances That Can Cause Sleep

  • Serotonin-cause slow wave sleep.
  • Muramyl peptide -low molecular substance than accumulates in CSF.
  • Nona peptide -from blood of animals.
  • Acetylcholine -released from efferent fibers of brain stem reticular
    formation activate many portion of brain—————-cause REM

Brain waves

  • Electrical recording from surface of brain(electrical potential) are
    brain waves and the entire record is called an


  • Thousand or millions of neurons must fire synchronously ,only the
    summated potential will be recorded.

Sleep-wake Cycle

  • When the sleep centers are not activated →
  • mesencephalic and upper pontile reticular activating nuclei are released
    from inhibition→
  • these areas become spontaneously active →
  • This excites both the cerebral cortex and the peripheral nervous system→
  • send numerous positive feedback signals (positive feedback activity)→
  • person become awake.
  • Then, after the brain remains activated for many hours, even the neurons
    themselves in the activating system presumably become fatigued →
  • positive feedback cycle fades and the sleep-promoting effects of the sleep
    centers take over, leading to rapid transition from wakefulness back to


  1. Sleep restores both normal levels of brain activity and normal “balance”
    among the different functions of the central nervous system -restoration
    or repair
  2. Neural maturation
  3. Facilitation of learning or memory
  4. Cognition
  5. Conservation of metabolic energy.
  6. Consolidation of learning.
  7. Remodelling of synaptic function.
  8. Dreaming

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