Stages of Sleep

Stage 1

• heart beat slows down
• muscle tension is reduced
• eyes may roll a little
• alpha waves a replaced by slower, smaller desynchronized activity

Stage 2

• EEG pattern becomes synchronized with large slower waves interrupted by periodic bursts of fast spiking activity called sleep spindles that last one or two seconds

Stage 3

• Large amplitude very slow waves (delta waves) dominate the EEG pattern and sleep spindles become less common
• Heart rate continues to fall as does body temperature.

Stage 4

• EEG recprdings consist purely of delta waves
• Metabolic rate reaches its lowest
• Arousal threshold is very high