NEUROPHYSIOLOGY OF SLEEP

DR MOHAMMED SUHAILAssistant Professor

Department of Physiology

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.

• DEFINITION:“ Physiological process by which bodily

functions are periodically rested person remains unconscious, can be aroused by sensory or other stimuli”

Physiological changes

• Cardiovascular system:– Heart rate– Cardiac output Decreases – Vasomotor tone– Blood pressure

• Respiratory system:– Tidal volume– Respiratory rate Decreases– Pulmonary ventilation

• 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

• 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

Types of sleepNeurophysiologist consider two types of

sleep–Non rapid eye movement sleep (NREM)–Rapid eye movement sleep (REM)

Stages

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

• REM

Relaxed wakefulness

• 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

Relaxed drowsiness

• 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

NREM ( slow wave sleep)

• Behavioural observation and EEG changesEach 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

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

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

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

REM( paradoxical sleep)

• 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

• 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.

• 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

AWAKE NREM REM

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%

• 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.

Genesis of sleep

• 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

• 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

–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

• Regular repeated monotonus stimuli put the children to sleep

• Genesis of REM– Discharge of Nor-epinephrine from neurons

located in pontine Reticular formation and locus cerulusPGO spikes are due to discharge of cholinergic neurons

Control of sleep waking cycle

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

• 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

• 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

• Humoral or chemical mechanism:– Neurotransmitters involved in sleep

serotoninnor-epinephrineacetyl cholinehypotoxindelta sleep inducing peptidesleep promoting factor ( factor S)

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

• The diurnal change in melatonin secretion from serotonin in the pineal gland functions as a timing signal to coordinate events with the light–dark cycle, including the sleep–wake cycle.

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.”

Narcolepsy:

• It’s a tetrad of – Excessive day time sleepiness – Cataplexy– Hypnogogic hallucination– Sleep paralysisExcessive day time sleepiness is primary symptomEDS may occur at the time of driving, eating, talking

• Patient falls asleep without warning • Cataplexy : triggered by emotions (laughter

anger) head nod and buckling of knee occur• Sleep paralysis

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

Summary • principal value of sleep is to restore natural

balances among the neuronal centers.• The entrainment of biological processes to the

light–dark 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 light–dark cycle, including the sleep–wake cycle.

THANKS