Posted by e-Medical PPT Wednesday, March 16, 2011
Sleep is a state of unconsciousness in which the brain is relatively more responsive to internal than to external stimuli
Mechanisms within the brainstem and hypothalamus regulate sleep through GABA and acetylcholine

Purpose of Sleep
NREM sleep may allow decrease in metabolic demand and allow replenishment of glycogen stores
Oscillating depolarization's and repolarizations consolidate and remove redundant or excess synapses

Circadian sleep rhythm
One of several intrinsic rhythms modulated by the hypothalamus
Without external stimulus, the suprachiasmatic nucleus sets the rhythm to approximately 25 hours
A nerve tract directly from the retina helps regulate us to 24 hours days.
Melatonin is a modulator of light entrainment and is secreted maximally by the pineal gland during the night

Normal Sleep Physiology
1 - light sleep, 5-10% of total sleep time, transition between awake and asleep
2 - 40-50% of total sleep time
3,4 - deep or delta wave sleep, occurs mostly early in the night
REM sleep, 20-25% of sleep
All 4 stages repeat in ultradian rhythm of about 90 minutes
There are 4-5 cycles in a normal night’s sleep
First REM- 10 minutes, but later REM periods may exceed 60 minutes

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