05. Stage of Sleep

Sleep

A naturally recurring state of reduced consciousness and activity in which the body and brain undergo restoration and regulation.

NREM Sleep

Non-Rapid Eye Movement sleep consisting of three stages: falling asleep, light sleep, and deep sleep.

NREM Stage 1 — Falling Asleep

The transition from wakefulness to sleep; characterized by decreased muscle activity, easy awakening, alpha waves, and a duration of a few minutes.

NREM Stage 2 — Light Sleep

A stage of continued relaxation characterized by slower brain waves, occasional sleep spindles, decreased heart rate and body temperature, and theta waves.

Sleep Spindles

Brief bursts of rapid brain-wave activity that occur during NREM Stage 2 sleep.

NREM Stage 3 — Deep Sleep

The most restorative stage of NREM sleep, characterized by body repair and growth, immune system strengthening, memory consolidation, difficulty awakening, and delta waves.

REM Sleep

Rapid Eye Movement sleep characterized by rapid eye movements, vivid dreams, muscle paralysis, and brain activity similar to wakefulness.

Rapid Eye Movements

Quick movements of the eyes that characterize REM sleep.

Muscle Paralysis During REM

A temporary inhibition of most skeletal muscles during REM sleep that prevents the person from physically acting out dreams.

Alpha Waves

Brain waves associated with relaxed wakefulness and the transition into sleep.

Theta Waves

Slower brain waves associated primarily with light sleep and NREM Stage 2.

Delta Waves

Very slow brain waves that dominate deep sleep or NREM Stage 3.

Beta Waves

Fast, low-voltage brain waves associated with active brain activity and commonly observed during REM sleep.

Memory Consolidation

The process by which newly acquired information and experiences are strengthened and stored as long-term memories during sleep.

Sleep Spindle

An occasional burst of rapid brain activity during NREM Stage 2 that is associated with sleep maintenance and memory processing.