Sleep Physiology Flashcards
What is the function of sleep during each stage?
NREM
Growth, tissue repair, clearance
Enhancement of immune system
Restoration of cerebral energy stores
REM
Processing of information
Unlearning irrelevant information
Memory consolidation
Facilitating learning and memory
Associated with active dreaming
Typically awaken in morning during an episode of REM sleep
Sometimes referred to as paradoxical sleep as the EEG is similar to wakefulness
What changes appear in the EEG from wakefulness to different sleep stages?
Awake – Normal active, random fast
Drowsy – Alpha Waves
Stage 1 Sleep – Theta waves
Stage 2 Sleep – Sleep spindles and k complexes
Stages 3,4 Sleep – Delta waves
Rem Sleep – Low voltage, random fast (similar to awake)
What is the sleep architecture for a young adult?
How is this different for a newborn?
For an older adult?
Sleeping for 8 hours straight
Stage 1: 2-8%
Stage 2: 45-55%
Stage 3/4: 13-23% (predominates for the first half of night)
REM: 20-25% (phasic and tonic, predominates last half of night)
Newborn: Sleeps 16 to 18 hours, more REM, shorter single episodes
Older adults are more fractioned, poorer sleep quality
What are the characteristics of NREM vs REM?
NREM
Dreams and nightmares may occur in NREM
Dreams usually not recalled
Induces slow-wave sleep, sometimes referred to as dreamless sleep
**REM **
Associated with active dreaming
Typically awaken in morning during an episode of REM sleep
Paradoxical sleep, EEG is similar to wakefulness
What are the two processes of the sleep-wake cycle?
Process H: Homeostatic process, the longer awake the greater propensity to sleep
Also known as Process S
Process C: Circadian oscillatory component affecting the propensity for sleep and waking
Internal biological clock
What is the time period for process C?
What is the anatomic basis for process C?
How is proces C set to match day length?
Approximate 24-hour period (26 hrs in reality)
Composed of about 10,000 neurons in the suprachiasmatic nucleus (Hypothallamus)
Entertained or reset to match the day length by the environmental photoperiod
Resetting is mediated through photoreceptors in the retina which send signals to the SCN
What specific factors are wake promoting and sleep promoting?
Wake promoting: Peptides (e.g. Substance P), Corticotrophin-releasing factor, Thyrotropin-releasing factors, Vasoactive Intestinal Peptide, Neurotenin, Epinephrine, Histamine, Glutamate, Cortisol, Serotonin (More important)
Sleep-Promoting: Peptides (e.g. opiates, encephalin), Delta-sleep inducing peptide, Alpha-melanocyte-stimulating hormone, Growth hormone-releasing factor, Y-aminobutyric acid (GABA), Cytokines, e.g. interleukins, Prostaglandin D2, Adenosine, Cholecystokinin, Somatostatin, Serotonin
How does the brainstem affect sleep-wake cycle?
What happens during NREM and REM to the activity of these?
Ascending projections from the brainstem affect sleep-wake cycle
Serotoninergic neurons (in raphe pallidus) Noradrenergic neurons (in locus coeruleus)
NREM sleep - Decrease activity from wakefulness during sleep
REM sleep
Virtually absent activity serotonoinergic and noradrenergic neurons, releases inhibition of cholinergic neurons
LDT/PPT and Gigantocellular tegmental field (FTG) nuclei increase in activity
What is the interplay of neuronal factors in determining wakefullness, NREM and REM?
- *Wakefulness** –Promoted by increased excitatory and decreased inhibitory neuromodulators and by circadian and homeostatic centers
- *NREM** – Sleep results when brainstem excitatory and hypothalamic circadian and homeostatic factors decrease
- *REM** – Sleep occurs when reduced norepinephrine and serotonin release inhibition of pontine PPT and LDT cholinergic neurons which activated REM
Comparisons in CNS activation between NREM and REM
NREM Sleep
Mean discharge rate of neurons decreased
Cerebral glucose utilization decreases
REM Sleep
Mean discharge rate of neurons increased in many regions (PGO spikes, Rapid eye movements)
Cerebral glucose utilization increased and resembles wakefulness
Cerebral blood flow greatly increased
What are differences in breathing patterns during sleep NREM vs REM?
NREM sleep
During wakefulness the breathing pattern is regular
Periodic breathing is noted in stages 1 and 2
Regular breathing in stages during 3 and 4
REM sleep
Irregularities in timing and amplitude of ventilator movements are noted
Paradoxical respiration – Thorax moves outward when abdomen moves inward
What are the overall ventilation changes in sleep?
Decrease in ventilation during sleep is greater than a concurrent decrease in metabolic rate
PaCO2 increases
Sleep induced hypoventilation
Unique to humans among animals
Metabolism slows at sleep onset, accelerates slowly at approximately 5:00 am
During deep sleep ventilation decreases more than metabolic rate
Increase in PaCO2 is due to alveolar hypoventilation
Blunted hypoxic and hypercapnic responses
What are hemodynamic changes in sleep?
Result from alteration in the ANS
Parasympathetic activity predominates during both NREM and REM sleep
Heart rate and cardiac output decrease
Cerebral blood flow decreases in NREM but increases in REM sleep
During phasic REM, blood pressure and heart rate are unstable due to phasic vagal inhibition and sympathetic activation
Overall, there is a slight decrease in total vascular resistance during sleep
What are the endocrine changes during sleep?
Growth hormone: Plasma concentrations peak 90 minutes after sleep onset
Higher in men than women
Duration of 1-3 hours, related to SWS
Sleep deprivation suppresses GH secretion
**Parathyroid: **Increased levels during sleep compared to awake state
Adrenocorticotropic hormone
Cortisol decreases with sleep onset
Cortisol levels lowest in early part of sleep, highest from 4:00 am – 8:00 am
What are the thermoregulatory changes in sleep? NREM vs REM
NREM Sleep: Lowered temperature set point
Shivering threshold lower
Sweating at normal ambient temperatures
REM Sleep: No regulation
No shivering response
No sweating at high ambient temperature
Body temperature drifts toward ambient temperature
