NEUROPHYSIOLOGY OF SLEEP

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NEUROPHYSIOLOGY OF SLEEP

• DR MOHAMMED SUHAIL
• Assistant Professor
• Department of Physiology

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GOALS

• To know types of sleep
• To know different stages of sleep
• To understand how complex neurohumoral changes
  occur when we go to sleep .
• To understand sleep disorders.

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• DEFINITION
• Physiological process by which bodily
  functions are periodically rested person remains
  unconscious, can be aroused by sensory or other
  stimuli

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Physiological changes

• Cardiovascular system
• Heart rate
• Cardiac output Decreases
• Vasomotor tone
• Blood pressure
• Respiratory system
• Tidal volume
• Respiratory rate Decreases
• Pulmonary ventilation

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• BMR
• decreases by 15
• Urine volume
• decreases, phosphate content of urine increases
• Secretions
• salivary and lacrimal secretion decreases
• sweat secretion increases
• Gastric secretion either remains unchanged or
  increases

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• Muscles
• completely relaxed , tone decreases
• Eyes
• pupils constricts
• Blood volume
• increases due to dilution of plasma
• CNS
• EEG shows appearance of delta waves
• Superficial reflexes remains unchanged
• Deep reflexes are reduced
• Light reflex is retained

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Types of sleep

• Neurophysiologist consider two types of sleep
• Non rapid eye movement sleep (NREM)
• Rapid eye movement sleep (REM)

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Stages

• Relaxed wakefulness
• Relaxed drowsiness
• NREM
• Stage 1
• Stage 2
• Stage 3
• Stage 4
• REM

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Relaxed wakefulness
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• Behavioural observation awake relaxed with eyes
  closed
• EEG mainly Alpha rhythm (8-12 Hz) changes to
  alpha block in response to external or internal
  stimuli

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Relaxed drowsiness
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• Behavioural observation
• Fatigue, tired, eyelids narrow and close, head
  may start to droop momentary lapse of alertness
  and attention sleepy but not asleep
• EEG decrease in alpha amplitude and
  frequency

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NREM ( slow wave sleep)
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• Behavioural observation and EEG changes
• Each successive stage have EEG pattern
  characterized by slow frequency and high voltage
  than previous one
• Significance
• Pulsatile discharge of Growth hormone and
  Gonadotropins from pituitary gland.
• Blood pressure heart rate and respiratory rate
  falls ---- metabolic restoration

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Stage-1

• Called light sleep
• Easily aroused by external stimuli or neck jerks
• Continuous lack of awareness
• EEG alpha wave reduce in frequency and amplitude

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Stage-2

• Called true sleep further lack of sensitivity
  to activation and arousal
• EEG
• characterized by sleep spindles
• burst of regular waves of frequency 14 to 15 Hz
  of short duration
• Cause formation of reverberating circuit
  between thalamus and cortex

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Stage-3

• Sleep further deepens
• EEG delta waves (1-2 Hz) appear as
  background with sleep spindles
• Stage-4
• Called deep sleep
• Slow high voltage delta waves

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REM( paradoxical sleep)
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• EEG resembles that of awake alert person
• rapid low voltage irregular waves
• ( Desynchronised pattern of EEG)
• Behavioural observation
• Deepest sleep, greatest muscular relaxation and
  fall in the muscle tone
• Extremely difficult to arouse the person

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• Saccadic eye movements from one fixation point to
  other- sweeping search of objects in the dreams
• Snoring- tongue fall
• Dreaming
• Blood pressure heart rate and respiration becomes
  irregular
• Bruxism, erection of penis ejaculation may occur.
  

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• Associated with large biphasic potential in group
  of 3-5
• Originate in the pons pass to LGB ultimately
  terminate in occipital cortex hence called PGO
  spikes
• PGO spikes activate bulboreticular inhibitory
  area leading to marked hypotonia

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• AWAKE NREM
  REM

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Sleep cycle

• Each cycle consist of NREM and REM
• Average total sleep period comprises of 4 to 5
  such cycles
• Each cycle repeats after 90 min
• NREM- 80
• REM- 20

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• REM time increases towards morning
• In full-term neonates REM Constitutes 50 of
  total sleep time.
• in Premature infants REM sleep occupies 80 of
  total sleep time.

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Genesis of sleep
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• Genesis of NREM
• Previously thought fatigue of reticular
  activating system but was found false
• But Sleep is an active phenomenon
• Synchronous activity in the brain is must for
  person to fall asleep

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• NREM Sleep is produced by two important factors
• Inhibition of reticular activating system by
  descending pathways from preoptic area and
  diagonal band of broca this prevents
  desynchronisation

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• Stimulation of sleep promoting mechanism
• rhythmic discharge of impulses from thalamus
  synchronization mechanism
• synchronising mechanism is influenced by
• Diencephalic sleep zone in hypothalamus and
  intralaminar and anterior thalamic nuclei
• Medullary synchronising zone in reticular
  formation of medulla

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• Regular repeated monotonus stimuli put the
  children to sleep

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• Genesis of REM
• Discharge of Nor-epinephrine from neurons located
  in pontine Reticular formation and
• locus cerulus
• PGO spikes are due to discharge of cholinergic
  neurons

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Control of sleep waking cycle

• There are two important mechanisms
• Neural mechanism
• Humoral mechanism or chemical mechanism

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• Neural mechanism
• Sleep and wakefulness alternate about once a day
  they manifest a circadian rhythm consisting of 8
  hrs sleep and 16 hrs awake state.
• basic rhythm is controlled by biological clock
  function of hypothalamic suprachiasmatic nucleus
  and pineal gland
• Sleep waking cycle involves
• arousal system
• and sleep producing system

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• Mechanism producing arousal
• Stimulation of sensory system
• Stimulation of midline Reticular formation
• Stimulation of raphe nuclei
• Mechanism that activate sleep producing system
• Removal of afferent stimuli l/t deceased activity
  of Reticular
• Stimulation of anterior and dorsal hypothalamic
  area

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• Humoral or chemical mechanism
• Neurotransmitters involved in sleep
• serotonin
• nor-epinephrine
• acetyl choline
• hypotoxin
• delta sleep inducing peptide
• sleep promoting factor ( factor S)

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• Transition from sleep to wakefulness involves
  alternating reciprocal activity of different
  group of RAS neurons

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• The diurnal change in melatonin secretion from
  serotonin in the pineal gland functions as a
  timing signal to coordinate events with the
  lightdark cycle, including the sleepwake cycle.

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Sleep Disorders

• Insomnia
• repeated difficulty with sleep initiation,
  maintenance, consolidation, or quality that
  occurs despite adequate time and opportunity for
  sleep and that results in some form of daytime
  impairment.

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Narcolepsy
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• Its a tetrad of
• Excessive day time sleepiness
• Cataplexy
• Hypnogogic hallucination
• Sleep paralysis
• Excessive day time sleepiness is primary symptom
• EDS may occur at the time of driving, eating,
  talking

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• Patient falls asleep without warning
• Cataplexy triggered by emotions (laughter
  anger) head nod and buckling of knee occur
• Sleep paralysis

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• Obstructive sleep apnea (OSA)
• Sleepwalking(somnambulism)

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Summary

• principal value of sleep is to restore natural
  balances among the neuronal centers.
• The entrainment of biological processes to the
  lightdark cycle is regulated by the SCN.
• The diurnal change in melatonin secretion from
  serotonin in the pineal gland functions as a
  timing signal to coordinate events with the
  lightdark cycle, including the sleepwake cycle.

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THANKS