(3) - Sleep Physiology-basic mechanisms of sleep &...

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1 Sleep Physiology-basic • In 1940 ` s Moruzzi & Magoun found that electrically + certain areas in the brain and brainstem produced cortical activation • arousal states appear to be determined by an interaction among the brainstem, hypothalamus, thalamus & basal forebrain • Dampening of arousal systems with concomitant active inhibition by thalamo- cortical systems produces sleep Basic mechanisms of sleep (cont) • Areas maintaining wakefulness include – oral pontine reticular formation – midbrain central tegmentum – posterior hypothalamus • Sleep promoting areas are located: – midline brainstem – dorsolateral medullary reticular formation – anterior hypothalamic preoptic region Interaction between sleep & wakefulness areas • Magnocellular nucleus basalis of Meynert located in the forebrain – intermingling of both sleep & arousal systems – sleep modulating center • both sleep and waking active sites – projections to neocortex and midbrain reticular formation – acetylcholine projections Sleep • Sleep is a behavioral state that differs from wakefulness by a readily reversible loss of reactivity to event ` s in one ` s environment. • Sleep is divided into stages based on: – electroencephalography (EEG) – electro-occulogram (EOG) – electromyogram (EMG) Sleep Stages • Non Rem (NREM) or slow wave sleep – I (light) theta, delta (low amplitude) horizontal eye – II (light) theta, delta, sleep spindles, K complexes – III (deep) high amplitude delta (20-50%) – IV (deep) high amplitude delta (>50%) • Rapid eye movement (REM) – EEG resembles awake state or NREM stage I – dramatic decrease in EMG activity Jet Lag
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2 Sleep • Electrical stimulation of nucleus tractus solitarius (NTS) produces slow wave sleep • Lesions in NTS produces cortical desynchronization (waking pattern of EEG) • NTS appears to inhibit more rostrally situated neurons in the ascending reticular activating system • Direct connections between NTS & major areas of the limbic system exist (ant. thalamus, hypothalamus, amygdala) Effect of pentobarbital on sleep Sleep (cont.) • Lesions in serotonin rich raphe nucleus produces insomnia • Parachlorophenylalanine (PCPA) a trytophan hydroxylase inhibitor also produces insomnia by blocking production of serotonin • SWS can be restored in PCPA induced insomnia by administration of 5 Hydroxytrytophan (5HTP) Sleep (cont) • Serotonin appears to modulate sleep through its effect on other hyponogenic factors in the anterior hypothalamus and suprachiasmatic nucleus • Serotonin is a melatonin precursor • Melatonin is synthesized and released by the pineal gland through sympathetic activation from the retino-hypothalamic tract Sleep (cont.) • Melatonin enhances sleep • prolonged bright light stimulation suppresses melatonin and sleep while subsequent melatonin injections can restore normal sleep patterns • Preoptic nucleus of ant. Hypothalamus appears to inhibit waking areas in the rostral
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(3) - Sleep Physiology-basic mechanisms of sleep &...

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