# 24 - NREM sleep

# NREM sleep:

© SPMM Course 
5. Physiology of sleep 
A. Measurement 
 Actigraphy: This is used to quantify circadian 
sleep-wake patterns and to detect movement 
disorders during sleep; it uses a motion sensor. 
 Polysomnography (PSG): This includes EEG, 
electromyogram (EMG), electrooculogram 
EOG. ECG, oximetry and respiratory monitor 
can also be added. PSG helps in the diagnosis 
and monitoring of sleep apnoea, narcolepsy, 
restless legs & REM behavioural disorder. Some 
of the terms used in PSG are 
o Sleep latency: time from ‘lights out’ to sleep onset. 
o REM latency: Time from sleep onset to first REM episode. Normally ~90 minutes in adults. 
o Non-REM latency: Time from sleep onset to first Non-REM episode. 
o Sleep efficiency: (Total sleep time/total time in bed) X 100. 
o Multiple sleep latency test: This is used to assess daytime somnolence and daytime REM 
onset in narcolepsy. 
B. Architecture 
The average length of sleep is approximately 7.5 hours per night. Sleep is made up of non-rapid eye 
movement (NREM) and rapid eye movement (REM) phases. 
NREM sleep: 
o 75% of adult sleep is NREM. Most 
physiological functions are markedly 
lower in NREM than in wakefulness 
(decreased muscle tone, respiration, 
temperature and heart rate). 
o NREM is classified as stages 1 to 4 with 
increasing amplitude and decreasing 
frequency of EEG activity. Stages 3 & 4 
together constitute slow wave sleep 
(SWS). SWS dominates initial part of the 
sleep. 
o Features of non-REM sleep includes 
 
Increased parasympathetic activity 
(decreased heart rate, systolic blood 
pressure, respiratory rate, cerebral blood flow) 
 
Abolition of tendon reflexes 
 
The upward ocular deviation with few or no movements. 
• 5% of sleep 
• Drowsy period. When awoken from this stage one 
denies being asleep. 
• Shows low voltage theta activity, sharp V waves. 
Stage 1 NREM sleep 
Stage 1 NREM sleep 
•45% of sleep 
•Shows the development of sleep spindles and K 
complexes. 
Stage 2 NREM sleep 
Stage 2 NREM sleep 
•12% of sleep 
•Shows <50% delta waves. 
Stage 3 NREM sleep 
Stage 3 NREM sleep 
•13% of sleep 
•Shows >50% delta waves. 
•Physiological functions are at the lowest 
Stage 4 NREM sleep 
Stage 4 NREM sleep 
DREAMS 
Dreaming occurs at all stages of sleep, but the 
content varies. In non-REM sleep the dreams 
are thought-like as though the person is solving 
a problem. In REM sleep the dreams may be 
illogical and bizarre.