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M05.08.01 Sleep Architecture
Sleep architecture refers to the structure and pattern of sleep cycles. It consists of two distinct states: Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep. These stages cycle throughout the night and are characterized by unique EEG patterns and physiological markers.
Components of Sleep
Non-Rapid Eye Movement (NREM) Sleep
NREM sleep is often referred to as “quiet sleep” and alternates with REM sleep during the night. It is divided into three stages based on electroencephalogram (EEG) criteria:
- Stage 1:
- Lightest stage of sleep
- Characterized by slowing of EEG rhythms and relaxation of muscles
- Theta waves appear on the EEG
- Stage 2:
- Represents the longest stage of sleep
- Sleep spindles and K-complexes emerge
- Theta waves dominate
- Stage 3 (Delta Sleep):
- The deepest stage of sleep
- Features delta waves, which are slow, high-amplitude waves (>75%)
- Known for its restorative properties, often decreases with age
NREM sleep is described as an “idling brain in a movable body.”
Rapid Eye Movement (REM) Sleep
REM sleep is often called “active sleep” or “paradoxical sleep” due to the contrast between an active brain and a nearly paralyzed body. Key characteristics of REM sleep include:
- Aroused EEG pattern similar to wakefulness
- Presence of saccadic (quick, jerky) eye movements
- Dreaming and sexual arousal occur
- Consolidation of memories by the hippocampus
REM sleep is known as an “awake brain in a paralyzed body.”
Sleep Stages and EEG Patterns
The table below summarizes the relationship between sleep stages and their corresponding EEG patterns:
| Stage of Sleep | Wave Associated | EEG Pattern |
|---|---|---|
| Stage 1 | Theta | Theta waves |
| Stage 2 | Sleep spindles, K complexes | Theta waves, spindles, K complexes |
| Stage 3 (Delta Sleep) | Delta | Delta waves (>75%), slow-wave sleep |
Sleep Facts Table
| Stage | Key Characteristics |
|---|---|
| Stage 2 | The deepest, restorative stage of sleep; tends to decrease in the elderly |
| Stage 3 (Delta Sleep) | Deepest, restorative stage of sleep; tends to decrease in the elderly |
| Sleep Latency | Time taken to fall asleep (5-15 minutes) |
| REM Latency | Time to first REM period (about 90 minutes) |
| REM Sleep | Increases in duration throughout the night; involved in memory consolidation by the hippocampus |
| NREM Sleep | More prevalent in the first half of the night |
Sleep Architecture Diagram
The figure below illustrates the stages of sleep, with Stage 1 and REM sleep shown together due to their similar EEG patterns.
| Sleep Stages Diagram |
|---|
| Awake, Stage 1, Stage 2, Stage 3, and REM stages alternate in cycles throughout the night. |
Points to Remember
- NREM sleep is divided into three stages: light sleep, deeper sleep, and delta sleep (deepest).
- REM sleep is characterized by vivid dreams, muscle atonia, and brain activity similar to wakefulness.
- NREM sleep predominates in the first half of the night, while REM sleep becomes more dominant as the night progresses.
- The sleep cycle repeats every 90 minutes on average, with the first REM period being shorter and the last one longer.
- Deep sleep (Stage 3) decreases with age, leading to lighter sleep in older adults.
Bibliography
- National Sleep Foundation – Sleep Architecture Overview
- American Academy of Sleep Medicine – Sleep Cycles and Stages
- Harvard Medical School – Understanding Sleep Cycles