sleep physiology Flashcards
Which of the following is correct
about recovery sleep following acute total sleep
deprivation?
On the first recovery night, large increase in NREM 3
sleep;
Rebound of REM sleep second night typical young;
little change in elders
Younger Subjects More Affected by
Sleep Deprivation than Elders
Normal older adults tolerate total sleep loss
better than young normal adults; older adults
tend to recover faster than younger;
Reaction times of young adults were significantly
slower after one recovery night compared with
older adults;
Young (not older) adults continued to have slow
reaction times on second recovery night.
Which of the following changes in plasma
levels are most likely after sleeping only 4 hours the
night before
Increased ghrelin, decreased leptin, increased evening
cortisol
Sleep deprivation and Ghrelin and Leptin
Ghrelin makes you Growl; Ghrelin stimulates hypocretin (“stay awake and get food”).
Leptin an adiokine released by fat cells signals satiety to brain, mediates appetite suppression (“stop eating, full”)
Leptin and sleep
Leptin-resistant: Some obese OSA patients have high leptin levels, but these do not suppress their appetite = leptin-resistant.
– CPAP treatment in such patients reduces elevated leptin levels, decreases abdominal visceral fat accumulation and improves glucose tolerance.
What are caffeine effects
caffeine = potent adenosine A1 receptor antagonist (combats rising homeostatic drive)
What is the effect Histamine on sleep
Histamine promotes wakefulness;
• Released by tuberomammillary nucleus (TMN) of posterior hypothalamus:
– Project widely to forebrain, brainstem and spinal cord;
• TMN neurons active when awake, increase their firing during W, decrease firing rates during drowsy states before sleep
• Destroy histaminergic TMN neurons in mice = can’t sleep
How do Histamine H1-Antagonists
Affect sleep
H1-receptor blockers increase sleepiness;
• First generation H1 antagonists (chlorpheniramine, diphenhydramine) are lipophilic so can readily cross blood brain barrier cause sedation & sleepiness;
• Second generation H-1 antagonists (certirizine, fexofenadine, loratadine) because hydrophilic do not cross BBB easily, less sedating stay awake
What is the role of Melanopsin and Glutamate
And neuropeptide Y in light entrainment
- Retinal ganglion cells contain melanopsin;
- Photic entrainment of circadian rhythms and pupillary responses to light especially 480 nm (blue/cyan range of visible light);
- Retinal ganglion cells project via retinohypothalamic tract (RHT) to suprachiasmatic nucleus (SCN);
- Release of glutamate from RHT stimulated by light, inhibits release of melatonin by pineal gland.
- Secondary photic entrainment pathway (lateral geniculate to SCN; geniculohypothalamic tract = neurotransmitter = neuropeptide Y;
- Glaucoma may selectively affect these photoreceptors in retina.
Hypocretin/Orexin Stabilize the Sleep and REM Switches = Excitatory
Stabilizes wakefulness;
• Produced by neurons in posterior lateral hypothalamus;
• Leptin and high glucose levels inhibits hypocretin (full, stop eating, go to sleep);
• Sleep deprivation increases hypocretin-1 transmission (stay awake and get some food).
• Ghrelin activates hypocretin (stay awake and get food);
• Human narcolepsy: deficiency of hypocretin-1;
– Canine narcolepsy = hypocretin-2 (dog is man’s best friend = #2).
Hypocretin neurons fire most vigorously during aroused awake state in which person actively exploring environment (e.g. walking – nice so you don’t fall);
• Hypocretin prevents transition from wake to REM sleep.
how is scoring central apneas in children performed
Score a central apnea which lasts 5 seconds in REM sleep if associated with a > 3 second EEG arousal and a 1 sec increase in chin EMG tone.
Central Apneas in Children Usually Require
Arousal or > 3% Desat to Score
When is Bradycardia in Central Apnea Scored in Infant < 1 year
New rule score a central apnea in children < 1 year if it lasts > 20 seconds or it is followed by significant bradycardia (HR <50/min > 5 sec or <60/min for > 15 sec);
• Why? Belief from neonatal apnea recordings that bradycardia throughout a central apnea makes it more pathological;
– One study of normal infants none had HR < 55/min for > 10 seconds related to CA.
What is the rule for scoring arousal
Score arousal after 20 seconds of stable sleep
Rule = score arousal during sleep if abrupt shift of EEG frequency including alpha, theta and/or frequencies > 16 Hz (but not sleep spindles) > 3 seconds, with > 10 seconds of stable sleep preceding the arousal:
– The 10 seconds of stable sleep required prior to scoring an arousal may begin in the preceding epoch, including a preceding epoch that is scored as stage W.
• To score an arousal in REM sleep additionally requires increase in chin EMG > 1 second.
Sleep-related Respiratory Changes
During Pregnancy in a Nutshell
Engorgement, hyper secretion, mucosal edema in nose, oropharynx, larynx, trachea from increased estrogen, increased progesterone, increased blood and interstitial volumes increased nasal resistance more NEGATIVE airway pressure during inspiration;
• Expanding uterus decreased Functional Residual Capacity (20-25%), Expiratory Reserve Volume (33-40%), and Residual Volume (22%);
• Late pregnancy airway closure increased ventilation-perfusion mismatch and decreased gas exchange especially supine;
• Progesterone increases respiratory rate increased minute ventilation and increased tidal volume leading to hypocapnia and respiratory alkalosis causing respiratory instability with episodes of central apnea at sleep onset and during REM sleep.
• Frequent awakenings cause respiratory instability and periodic breathing;
What is the role of Progesterone on sleep
Progesterone targets GABA receptors rises in progesterone has soporific and sedative effects;
Animal models progesterone decrease NREM latency, W and REM sleep;
Smooth-muscle relaxation leads to frequent urination, heartburn, rhinitis leading to nocturnal awakenings;
Raise body temperature (sleep better cooler than warmer)
What is the effect of Estrogen on sleep
• Decrease REM sleep neurons in VPLO area; i• Cause vasodilation which predisposes to nasal obstruction and lower extremities edema
What Protects Pregnant Women From
Sleep Disordered Breathing?
• Progesterone increases tone of upper airway dilator genioglossus muscle activity and increases responsiveness to CO2 during sleep;
• R-shift oxyhemoglobin dissociation curve and increase HR,increase stroke volume, and increase cardiac output with increase peripheral vascular resistance improves O2 delivery to placenta and maternal tissues;
less time supine as pregnancy advances.
Describe changes in Infant sleep as they age
A. A dominant posterior rhythm when awake of 3-4 Hz first seen 3-4 months of age.
B. K-complexes first appear frontal regions 5-6 months of age;
C. Short REM sleep latencies in infants < 3 months post-term; (50% of TST spent REM sleep at term)
D. Sleep cycles in newborn term infants last 40-60 min;
E. Sleep spindles first appear over midline central region at 44-48 weeks conceptional age.
When Sleep spindles begin to appear in infant
First seen 43 weeks CA (3 weeks post-term, usually present age 2-3 months
When do K-complexes appear in infant
First appear age 5-6 months post-term maximal over the frontal regions.
NREM 3 Slow Wave Activity(0.5-2 Hz)
First seen age 2-3 months post-term, usually present age 4-4.5 months post-term, maximal over frontal regions.
When is REM first seen in Infants
First apparent by 30-32 weeks conceptional age (whereas full term in 38-42 weeks CA). Sleep in term neonate = 50% REM, 50% non-REM (quiet sleep)
at what age can we Distinguish sleep stages in infancy
As early as age 4 – 4.5 months and usually by age 5-6 months.
Dominant waking posterior rhythm (DPR):
– First appears, ages 3-4 months term, 3-4 Hz
– 5-6 Hz by 5-6 months, 70% have 6-8 Hz by 1 year;
– Most have 8 Hz by 3 years (range 7.5-9.5 Hz);
– Normal in young and older adults: > 8.5 Hz:
• Younger adults average 10.2 Hz; older adults 9.7 Hz;
• Normal for “healthy old” DPR >8.5 Hz.
Which of the following is the main
neurotransmitter regulating the pineal gland?
Correct answer = Norepinephrine
Describe the Regulation of melatonin
During daylight, the suprachiasmatic nucleus (SCN) inhibits paraventricular nucleus which inhibits melatonin secretion;
• Sun sets, inhibition of melatonin secretion diminishes, permitting melatonin to be secreted by pineal gland.
– Melatonin synthesized from tryptophan;
– Norepinephrine is the main neurotransmitter regulating pineal gland:
– Binds to melatonin receptors triggers cascade of secondary messengers which generate cyclic AMP which prompts
melatonin to be synthesized from tryptophan
GI effects of sleep
Unstimulated gastric acid secretion in normals has prominent circadian rhythm:
– Peaks 10 pm to 2 am; Lowest 5 am to 11 am.
– Vagal stimulation most likely to regulate this circadian rhythm, lost after vagotomy;
– Plasma gastrin levels do not have circadian rhythm.
• A solid meal before bedtime decreases sleep latency more than a liquid meal;
• Decreased gastric motility, salivation and swallowing during sleep;
• Decreased mucosal acid contact during sleep.
Wakefulness-promoting brain regions and respective neurotransmitters:
– PPT/LDT: acetylcholine – Posterior Lateral hypothalamic perifornical region: hypocretin/orexin – Locus coeruleus: norepinephrine – Tuberomammillary nucleus: histamine – Substantia nigra: dopamine – Dorsal raphe nuclei: serotonin
What are the Respiratory changes occurring with sleep
Changes in Blood Gases Sleep Compared to Wakefulness
• During sleep (compared to wakefulness);
– PaCO2 increases 2-8 mm Hg;
– PaO2 decreases 3-10 mm Hg;
– SpO2 decresees 0-2%;
– Minute ventilation decreases0.5-1 L/min
• Periodic breathing especially NREM 1 sleep; if paCO2 drops below PaCO2 threshold, relative hypocapnia sensed at medullary chemoreceptor and induces hypoventilation/apnea until paCO2 rises. – Most apparent in people with Cheyne-Stokes respiration.
Circadian-mediated decline in body temperature at night activates which neurons?
Correct answer = sleep-promoting GABA neurons
A. GABA
Sleep spindles generated where
in brain? What neurotransmitter
associated with them?
Thalamus (reticular nucleus) neurons contain GABA; Sleep spindles are hyperpolarized as sleep begins (reduces arousal). This produces a discharge of thalamic neurons which is transferred to a network of thalamo-cortical neurons.
Lesions where in the hypothalamus produce narcolepsy ?
lesion in posterior and lateral hypothalamus severe hypersomnia.
Lesions where in the hypothalamus produce insomnia?
Lesion preoptic area and basal forebrain severe insomnia;
Acetylcholine (cholinergic) neurons are located where in the brain
Pons and basal forebrain; early atrophy of these neurons predispose to sleep disorders in Alzheimer’s disease.
Which thalamic nucleus is preferentially affected in fatal familial insomnia?
Dorsomedial thalamus
Physiological mechanism underlying sleep drunkenness or sleep inertia?
VPLO abnormality
Injection of physostigmine et al. cholinergic agonists into LLD/PPT in humans would be expected to induce what sleep/wake state?
Cholinergic agents into dorsal pons LDT/PPT expected to induce REM sleep
Which neurotransmitter is contained in the projections from the ascending reticular activating system?
Norepinephrine/noradrenaline
VLPO (Ventral Lateral Preoptic) area important in regulation of which sleep/wake state?
VPLO promotes NREM sleep. Inhibitory GABAergic VPLO projections decrease ARAS neurons as NREM sleep begins and deepens. VPLO inhibit brainstem nuclei involved in EEG arousal, and inhibit histamine wakefulness promoting neurons in TMN
A secondary indirect pathway by which light reaches the SCN is via the lateral geniculate and geniculohypothalamic tract. What is the neurotransmitter for the geniculohypothalamic tract?
the lateral geniculate-SCN (geniculohypothalamic tract) neuropeptide Y as its neurotransmitter.
1-4 Hz delta activity (slow wave activity) of NREM 3 are generated by what mechanism?
Burst rhythmic discharges in thalamocortical neurons.
What are the wake-maintenance zones?
2 circadian peaks in alertness typically late morning and early evening. Difficult to fall asleep during these.
What are sleep-maintenance zones?
2 circadian troughs in alertness (increased sleep propensity) typically in early morning (e.g. 1-3 am) and early-mid afternoon; easier to fall asleep then
Sleep requirements in older adults compared to younger adults?
Sleep requirements do NOT decline with aging. However, aging associated with greater nocturnal sleep disturbance, EDS, daytime napping, greater prevalence of insomnia, OSA, CSA, PLMs, RLS, RBD, and advanced sleep phase type.
Which sleep disorders/medications are associated with ↑SOL, ↓ SE, ↓ TST and ↑WASO?
Disorders reporting insomnia and stimulant medication use.
Which sleep disorders/medications are associated with ↓SOL, ↑ SE, ↑ TST and ↓ WASO
Sleep deprivation, disorders presenting with EDS, sedating medications. ↑↓
What is the effect of oral melatonin on phase when taken in morning? In evening?
Melatonin synthesized and released by the pineal gland; secretion inhibited by light exposure. Melatonin when taken in morning DELAYS phase; taken in evening, ADVANCES phase.
What is the effect of oral melatonin on phase when taken in morning? In evening?
Melatonin synthesized and released by the pineal gland; secretion inhibited by light exposure. Melatonin when taken in morning DELAYS phase; taken in evening, ADVANCES phase.
What is the main neurotransmitter for REM
sleep?
Acetylcholine is the main neurotransmitter in
REM sleep
Which neurotransmitter responsible for REM sleep without atonia?
Glycine is the main inhibitory neurotransmitter in spinal cord and responsible for REM sleep without atonia (RSWA)
GABA-producing neurons in brain located
where?
GABA-producing neurons are located in VPLO = Ventrolateral pre-optic hypothalamus
Sleep pressure increases in relationship to prior wakefulness and correlates with a rise in CSF levels of what?
Homeostatic sleep pressure rises with increasing levels of CSF adenosine.
Production of which hormones increase during
sleep?
ADH (increased renal water reabsorption); GH and prolactin (during NREM 3) Renin (during NREM sleep) Testosterone (during REM sleep)
Production of which hormones decrease during
sleep?
Cortisol levels decrease during NREM 3 sleep; Insulin secretion
What is the effect of sleep on the cardiovascular,
CV system: decrease HR, CO and BP (NREM and tonic
REM sleep); decreased frequency of PVCs;
What is the effect of sleep on the GI,
GI system: ↓swallowing rate; ↓ salivary
production; ↓ esophageal and ↓ intestinal
motility
What is the effect of sleep on renal systems?
Renal system↓ glomerular filtration but ↑ADH production (increased renal water reabsorption).
What is the effect of sleep deprivation on autonomic nervous system activity? Cortisol, ghrelin and insulin resistance?
Sleep deprivation increases SNS activity, cortisol
secretion, insulin resistance and ghrelin
Criteria for terminating a nap in MWT?
Nap trial in MWT is terminated if: 1) 3 consecutive epochs of N1 sleep; 2) 1 epoch of any other sleep stage; 3) No sleep after 40 minutes
To score an arousal on a PSG what is
needed?
During NREM arousals – require changes in EEG only REM arousals – require changes in EEG and EMG EEG changes – abrupt EEG frequency shift (alpha, theta or > 16 Hz, but not spindles) 3 seconds and preceded by 10 seconds of stable sleep EMG changes – increase in chin EMG 1 second
What are the clinical correlates of phasic activity of REM sleep
Rapid eye movements, twitching of distal muscles, middle ear activity, and PGO (ponto-geniculo-occipital) waves;