N EUROPHYSIOLOGY OF S LEEP DR MOHAMMED SUHAIL Assistant 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 sleep Neurophysiologist 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 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

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 cerulus PGO 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 serotonin nor-epinephrine acetyl choline hypotoxin delta sleep inducing peptide sleep 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 paralysis Excessive day time sleepiness is primary symptom EDS 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.

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