ABSTRACT
A. Sleep: characterized by the complex interplay of physiologic and behavioral factors
B. Behavioral Definition of Sleep: a reversible physiologic state of decreased perception of and responsiveness to external stimuli
A. No Single Accepted Model
B. Several Proposed Theories 1. Body repair 2. Brain restoration 3. Thermoregulation and energy conservation 4. Maintenance of immunocompetence 5. Memory consolidation and learning 6. Unlearning
A. Animal Experiments 1. Total sleep deprivation in rats resulted in death of
unclear cause after a mean of 21 days a. Proposed mechanism: bacteremia, sepsis b. High metabolic rate, weight loss, decreased body
temperature, and ulcerative skin lesions on tail and extremities preceded death
2. Partial sleep deprivation: similar changes but slower rate of progression (death occurred after a mean of 37 days)
3. Recovery sleep resulted in survival
B. Human Experiments 1. Most normal adults need 7.5 to 8 hours of nocturnal sleep
2. Total sleep deprivation of 5 to 10 days: development of tremor, ptosis, diminished corneal reflex, hyperreflexia, nystagmus a. Electroencephalography (EEG): increased theta and
delta frequencies while awake with eyes closed and diminished alpha activity
b. During recovery sleep: large amounts of slow wave sleep (SWS), i.e., SWS rebound, occur during first night; large amounts of rapid eye movement (REM) sleep occur during second night
3. Partial sleep deprivation of 2 hours or more per night: impaired psychomotor function, mood changes, increased risk of falling asleep while driving, motor vehicle accidents a. Chronic partial sleep deprivation (4-6 hours nocturnal
sleep) for 2 weeks: cumulative deficits on objective cognitive testing
b. Recent studies on sleep-deprived medical and surgical residents showed increased medical errors: impairment of electrocardiogram interpretation, longer time to complete procedures, surgical errors, increased complication rate
c. Sleep-deprived residents also showed deterioration of performance on psychomotor testing, increased risk of falling asleep while driving, increased number of traffic citations and accidents
d. Selective REM sleep deprivation leads to REM rebound during recovery sleep
4. Subjective sleepiness increases with acute sleep loss but does not worsen significantly further with persistent sleep deprivation
A. Sleep-Wakefulness Control Mechanisms: exerted by specific neuronal groups of brainstem ascending reticular activating system (ARAS) (Table 19-1)
1. Pedunculopontine nucleus (cholinergic) 2. Laterodorsal tegmental nuclei (cholinergic) 3. Locus ceruleus (noradrenergic) 4. Raphe nuclei (serotonergic)
B. ARAS: projects to intralaminar thalamic nuclei, posterior hypothalamus, basal forebrain
C. Additional Neurotransmitters Involved in SleepWake Regulation
1. Histamine (tuberomamillary nucleus): promotes arousal and wakefulness
2. Dopamine (ventral tegmental area): promotes wakefulness
3. Hypocretin (dorsolateral hypothalamus): promotes arousal
4. Other sleep-promoting neurochemicals: γ-aminobutyric acid (GABA) (ventrolateral preoptic area), galanin, adenosine, cytokines (interleukins, C-reactive protein, tumor necrosis factor α), prostaglandin D2, delta sleep-inducing peptide, muramyl peptides, growth hormone-releasing factor, cortistatin, opioid peptides
D. Sleep Stages: non-rapid eye movement (NREM) sleep and REM sleep
1. Normal sleep a. 4-6 cycles per night of NREM sleep, followed by REM
sleep b. Cycle duration: about 90 minutes c. NREM sleep consists of stages I, II, III, and IV d. NREM sleep gets progressively deeper and arousal
threshold increases from stage I to IV e. Stage I is typically followed sequentially by stages II, III,
and IV (stages III and IV = SWS) and again stage II before REM sleep
f. Throughout the night
1) SWS periods shorten 2) REM sleep periods lengthen 3) Thus, most NREM sleep occurs during first half of
the night, followed by predominantly REM sleep in the second half
2. Typical sleep architecture in a young adult (Fig. 19-1) a. Stage I: <5% b. Stage II: 40% to 60% c. Stage III/IV (SWS): 10% to 20% d. REM sleep: 20% to 25%
E. NREM Sleep: general characteristics 1. Synchronized, rhythmic EEG activity 2. Decreased cerebral blood flow 3. Decreased skeletal muscle tone 4. Decreased heart rate, blood pressure, respiratory tidal
volume
F. Stage I 1. Dropout of occipital alpha rhythm 2. Low-amplitude theta activity 3. Positive occipital sharp transients of sleep (POSTS) 4. Vertex waves (V waves) over frontocentral leads 5. Slow rolling eye movements (horizontal) 6. Partial relaxation of voluntary muscles
G. Stage II (Fig. 19-2) 1. K complexes: central high-amplitude, diphasic waves,
>0.5 second in duration 2. Sleep spindles: central 12 to 14-Hz activity of 0.5 to 2
seconds’ duration 3. POSTS, V waves, slow rolling eye movements may
occasionally persist
H. Stage III: synchronized, high-amplitude delta activity (≤2 Hz, ≥75 μV, 20%-50% of a 30-second epoch)
Sleep is a physiologic state, and deprivation leads to derangements of cognitive and psychomotor function.
