Page 350 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Sleep Disorders
Normal sleep requires the interplay of several peptides that are broken down again during
cerebral structures, among them the loci ceru- sleep. It is possible that serotonin stimulates
leus and subceruleus (norepinephrine being the formation of sleep factors, because inhibit-
the transmitter), the raphe nucleus (serotonin ing serotonin formation, release or action (e.g.,
as transmitter), tractus solitarius nucleus, and by the antihypertensive drug reserpine) causes
Systems neurons in the hypothalamus. A lesion in the insomnia.
subceruleus nucleus results in rapid eye move-
The sleep-inducing peptides cause “sleep
ment (REM) insomnia (see below); lesions in
pressure” (NREM sleep pressure or slow wave
sleep [SWS]; → C1). The net sleep pressure is
the raphe nuclei or the anterior hypothalamus
Neuromuscular and Sensory posterior hypothalamus cause narcolepsy. Ex- and the reciprocal of the REM sleep pressure
the difference between sleep pressure (violet)
lead to (transient) insomnia; lesions in the
(green) that follows a circadian rhythm essen-
citation of the tractus solitarius nucleus (e.g.,
by gastric distension) causes fatigue. Sleep is
tially in parallel to body temperature and sim-
ilar bodily parameters, such as “readiness for
also very dependent on the circadian rhythm,
in that destruction of the central rhythm gen-
activity and effort”. The ability to fall asleep is
a function of this net sleep pressure.
erator, the suprachiasmatic nucleus (SCN)
When experiencing a change of time zone
leads to irregular periods of falling asleep and
circadian rhythm at first continues to oscillate
ated by the ascending reticular activating sys-
in the original phase. When the day is short-
tem (ARAS), a connection between the reticu-
10 of difficulty in awakening. The latter is medi- (jet lag; → C2) or when doing shift work, the
ened, it is impossible to go to sleep at the local
lar formation via intralaminar nuclei of the
thalamus to large areas of the brain (→ A). De- time because of the low net sleep pressure.
struction of the intralaminar thalamic nuclei When the day gets longer, the sleep pressure
(e.g., by ischemia) leads to somnolence. De- is increased by the longer waking period and
synchronization between subcortical activity falling asleep at the local time is no problem.
and cortical sleep may be the cause of sleep- The subsequent circadian rhythm, however,
walking (somnambulism). causes early awakening.
Disorders of the regulation of breathing Falling asleep is also disturbed by delayed
during sleep have been held responsible for sleep phase insomnia (→ C3), caused by an in-
the sudden infant death syndrome (SIDS) and flexible circadian rhythm that cannot be short-
sleep apnea in adults. Metabolic alkalosis is ened. When going to sleep too early the net
thought to favor sleep apnea. In addition, de- sleep pressure is too low. During chronother-
creased muscle tone during sleep promotes apy a lengthened daily rhythm (27 hours) is
the collapse of the airways, apnea, and hypox- forced upon the patient until the desired circa-
ia. dian periodicity has been obtained.
Normally one passes through several Depression (→ C4) possibly reduces the for-
phases of varying depth during sleep (→ B). mation of sleep-inducing peptides through a
During one night there are typically about 5 lack of serotonin (→ p. 350). This results in a
phases of REM sleep (→ B, marked in red), dur- decrease in net sleep pressure (red line) and
ing which bursts of excitation from the brain difficulty in falling asleep. The sleep pressure
stem produce twitches in the otherwise hypo- can be increased by sleep deprivation the next
tonic musculature. Several phases of non-REM day, and thus normal sleep can be achieved.
(NREM) sleep must be passed through before A raised level of excitement makes falling
REM sleep is reached, whereby increasing asleep more difficult and reduces the duration
depth of sleep correlates with decreasing fre- of sleep (→ C5). Anxiety about insomnia raises
quency of the EEG waves. Chronic use of sleep- this level and is thus counterproductive.
ing pills leads to lighter NREM sleep and only
occasional REM phases.
340 During the awake phases endogenous sleep
factors accumulate, such as the sleep-inducing
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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