What the exam asks
- Scenario identification: Given a patient’s symptoms or an EEG readout, identify the sleep stage (NREM 1–3 or REM) or sleep disorder.
- Circadian disruptions: Explain how shift work or jet lag alters biological rhythms and waking cognition.
- Research and data analysis: Interpret sleep-deprivation experiments (e.g., testing REM rebound or memory consolidation) in AAQ or EBQ prompts.
Core ideas
Consciousness and circadian rhythms
Consciousness is our varying level of awareness of internal states (thoughts, feelings) and external stimuli. Wakefulness (high awareness) and sleep (a periodic, natural, reversible loss of consciousness with low awareness) are two distinct states along this continuum.
The sleep/wake cycle follows a circadian rhythm—an internal biological clock operating on a roughly 24-hour cycle. Light hits the retina, signaling the suprachiasmatic nucleus (SCN) in the hypothalamus to instruct the pineal gland to decrease melatonin (promoting wakefulness); darkness triggers melatonin release (promoting sleepiness). Jet lag (crossing time zones) and rotating shift work desynchronize the internal circadian clock from external light cues, impairing mood, alertness, and physical health.
Stages of sleep
A full sleep cycle lasts about 90 minutes and repeats 4–5 times per night. Before entering Stage 1, relaxed, awake brains show slow alpha waves (compared to active beta waves during alert wakefulness).
| Stage | EEG Waveform | Key Characteristics |
|---|---|---|
| NREM Stage 1 | Theta waves (slow, irregular) | Lightest sleep (a few minutes). Features hypnagogic sensations: fleeting visual/auditory hallucinations or a sudden sensation of falling (myoclonic jerk). |
| NREM Stage 2 | Theta waves interrupted by sleep spindles and K-complexes | About 20 minutes. Sleep spindles are rapid bursts of rhythmic brain activity that aid memory processing; K-complexes are large single waves that suppress arousal in response to external stimuli. |
| NREM Stage 3 | Delta waves (large, slow waves) | Deep, slow-wave sleep (~30 minutes). Hardest to awaken; heart rate, breathing, and brain activity drop to their lowest levels. |
| REM Sleep | Sawtooth beta-like waves (fast, irregular, resembling wakefulness) | Rapid Eye Movement (~10 minutes early in the night, longer later). Vivid story-like dreams occur. Called paradoxical sleep because the brain is internally active while the body is externally paralyzed (atonia, controlled by the brainstem). |