Chapter 10: Normal Sleep and Sleep Disorders
I. Normal Awake and Sleep States
Understanding normal sleep is essential for diagnosing sleep disorders. Humans have an internal biological clock that governs the sleep-wake cycle. In the absence of external time cues (like sunlight), this circadian cycle runs on a rhythm closer to 25 hours, not 24.
These external cues, called zeitgebers, help synchronize our internal clock with the 24-hour day.
The Awake State
- EEG Waves: An electroencephalogram (EEG) of an awake person shows two main types of brain waves:
- Beta Waves: Fast, low-amplitude waves seen during active mental concentration.
- Alpha Waves: Slower waves seen when a person is relaxed with their eyes closed.
- Sleep Latency: The time it takes to fall asleep is normally less than 10 minutes.
The Sleep State and Sleep Architecture
Sleep is divided into two major types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. A typical night's sleep cycles through these stages in a predictable pattern called sleep architecture.
| Sleep Stage | Associated EEG Pattern | % of Sleep Time | Key Characteristics |
|---|---|---|---|
| NREM Stage 1 | Theta Waves | 5% | Lightest stage; transition from wakefulness. Slowed pulse/breathing. |
| NREM Stage 2 | Sleep Spindles & K-complexes | 45% | Largest percentage. Bruxism (tooth grinding) can occur. |
| NREM Stages 3 & 4 (Delta) | Delta Waves (Slow-Wave) | 25% | Deepest sleep. Associated with sleepwalking, night terrors, and enuresis. |
| REM Sleep | "Sawtooth" waves | 25% | Dreaming occurs. Skeletal muscle atonia. Increased pulse/BP. Penile/clitoral erection. |
Key Features of Sleep Cycles
- A complete sleep cycle (from Stage 1 to REM) lasts about 90 minutes.
- REM Latency: The time from falling asleep to the first REM period is normally about 90 minutes.
- Distribution: Most Delta (deep) sleep occurs in the first half of the night. REM periods become longer and more frequent in the second half.
- REM Rebound: If deprived of REM sleep (e.g., sedatives, awakenings), a person will experience increased REM sleep the following night.
Neurotransmitters and Sleep
- Acetylcholine (ACh): Increases sleep efficiency and REM sleep.
- Dopamine: Decreases sleep efficiency. (Antipsychotics improve sleep by blocking dopamine).
- Norepinephrine: Decreases sleep efficiency and REM sleep.
- Serotonin: Increases sleep efficiency and Delta sleep.
Sleep Changes with Age
Sleep architecture changes significantly across the lifespan. Elderly individuals experience a significant reduction in Delta (deep) sleep and more frequent nighttime awakenings, leading to poor sleep quality and daytime fatigue.
- Sleep Latency: Increases (>10 min).
- REM Latency: No major change (unlike depression where it is shortened).
- Sleep Efficiency: Decreases.
II. Classification of Sleep Disorders
The DSM-5 categorizes sleep disorders into several main groups:
- Sleep-Wake Disorders: Problems with the timing, quality, or amount of sleep. Includes insomnia, hypersomnolence, and narcolepsy.
- Breathing-Related Sleep Disorders: Disrupted sleep due to breathing problems, primarily sleep apnea.
- Parasomnias: Abnormal behaviors or physiological events during sleep. Includes bruxism, sleepwalking, sleep terror disorder, and nightmare disorder.
III. Major Sleep Disorders
A. Insomnia
- Definition: Difficulty falling asleep or staying asleep, leading to daytime impairment.
- Psychological Causes:
- Major Depressive Disorder: Key features include terminal insomnia (waking too early), long sleep latency, and short REM latency.
- Bipolar Disorder: Manic/hypomanic patients have trouble falling asleep and require less sleep.
- Anxiety Disorders: Difficulty falling asleep.
- Physical Causes: Stimulants (caffeine), withdrawal from sedatives (alcohol, benzodiazepines), pain.
B. Breathing-Related Sleep Disorder (Sleep Apnea)
Repeated stops in breathing during sleep, causing low oxygen/high CO₂ (respiratory acidosis) and frequent awakenings. Results in severe daytime sleepiness and morning headaches.
- Central Sleep Apnea: No respiratory effort is made. More common in elderly.
- Obstructive Sleep Apnea: Respiratory effort occurs, but airway is obstructed. Common in obese, middle-aged men (snoring).
C. Narcolepsy
A disorder characterized by uncontrollable "sleep attacks" during the day, despite normal night sleep. Characterized by a very short REM latency (<10 min).
The Narcolepsy Tetrad
- Excessive Daytime Sleepiness: The primary symptom.
- Cataplexy: Sudden, complete loss of muscle tone triggered by strong emotion (laughter/surprise). Patient remains conscious.
- Hypnagogic/Hypnopompic Hallucinations: Vivid hallucinations while falling asleep (hypnagogic) or waking up (hypnopompic).
- Sleep Paralysis: Brief inability to move or speak immediately upon waking.
IV. Management of Sleep Disorders
| Disorder | Management Strategies |
|---|---|
| Insomnia |
1. Sleep Hygiene: Consistent schedule, bedtime ritual, avoid caffeine, exercise. 2. Psychoactive Agents: Limited use. Antidepressants if due to depression. |
| Obstructive Sleep Apnea |
1. Weight Loss: If overweight. 2. CPAP: Continuous Positive Airway Pressure (primary treatment). 3. Surgery/Stimulants (less common). |
| Narcolepsy |
1. Stimulant Agents: Modafinil or methylphenidate for daytime sleepiness. 2. Scheduled Daytime Naps: Helps refresh and make up for lost REM. |
High-Yield Exam Points
- 🔥 Delta Sleep (Stage 3/4): Deepest sleep, site of sleepwalking and night terrors.
- 🔥 REM Sleep: Associated with dreaming, atonia, and penile/clitoral erection.
- 🔥 Elderly Sleep: Decreased Delta sleep, increased nighttime awakenings.
- 🔥 Narcolepsy Tetrad: Sleepiness + Cataplexy + Hallucinations + Paralysis.
- 🔥 Depression Sleep: Terminal insomnia (early waking), short REM latency.
- 🔥 Neurotransmitters: ACh ↑ REM; Serotonin ↑ Delta.
Practice MCQs
Q1. The parents of a 5-year-old boy report that the child often screams during the night. During these disturbances, the child sits up, opens his eyes, and “looks right through them,” and they are unable to awaken him. The child has no memory of these experiences. During these disturbances, the child’s EEG is most likely to be primarily characterized by:
Explanation: The child is experiencing a sleep terror disorder. These events, along with sleepwalking, occur during the deepest stage of NREM sleep (Stages 3 & 4), which is characterized by slow, high-amplitude delta waves. Sawtooth waves are seen in REM sleep.
Q2. During a sleep study, a physician discovers that a patient shows too little REM sleep during the night. Theoretically, to increase REM sleep, the physician should give the patient a medication aimed at increasing circulating levels of:
Explanation: The neurotransmitter acetylcholine (ACh) is known to increase both the amount of REM sleep and overall sleep efficiency. Norepinephrine and dopamine decrease REM sleep.
Q3. During a sleep study, a male patient’s EEG shows primarily sawtooth waves. Which of the following is most likely to characterize this patient at this time?
Explanation: Sawtooth waves are a hallmark of REM sleep. REM sleep is characterized by high brain activity, dreaming, muscle paralysis (atonia), and physiological arousal, which includes penile erection.
Q4. During a sleep study, a female patient’s EEG shows primarily delta waves. Which of the following is most likely to characterize this patient at this time?
Explanation: Delta waves are characteristic of NREM Stages 3 & 4 (deep sleep). Parasomnias like sleepwalking (somnambulism) and night terrors occur during this stage.
Q5. An 85-year-old patient reports that he sleeps poorly. Sleep in this patient is most likely to be characterized by increased:
Explanation: Sleep in the elderly is characterized by poor quality, including decreased sleep efficiency, decreased REM sleep, and decreased Delta sleep. A key feature is significantly increased nighttime awakenings.
Q6. A woman reports that most nights during the last year, she has lain awake in bed for more than 2 hours before she falls asleep. After these nights, she is tired and forgetful and makes mistakes at work. Of the following, the most effective long-term treatment for this woman is:
Explanation: This is chronic insomnia. The most effective long-term, non-pharmacological treatment is improving sleep hygiene, which includes the development of a consistent, relaxing bedtime ritual.
Q7. A 22-year-old medical student who goes to sleep at 11 pm and wakes at 7 am falls asleep in the laboratory every day. He tells the doctor that he sees strange images as he is falling asleep. Which of the following is this student most likely to experience?
Explanation: This student shows classic signs of narcolepsy: excessive daytime sleepiness and hypnagogic hallucinations. Cataplexy is the other key feature of the disorder.
Q8. The medical student in the previous question is diagnosed with narcolepsy. The most effective first step in management is:
Explanation: The primary treatment for managing the excessive daytime sleepiness of narcolepsy is a stimulant agent (e.g., modafinil).