A 20-year-old college student presents to the emergency room complaining of insomnia for the past 48 hours. He explains that although his body feels tired, he is "full of energy and focus" after taking a certain drug an hour ago. He now wants to sleep because he is having hallucinations. His vital signs are T 100.0 F, HR 110 bpm, and BP of 150/120 mmHg. The patient states that he was recently diagnosed with "inattentiveness." Which of the following is the mechanism of action of the most likely drug causing the intoxication?

Increases presynaptic dopamine and norepinephrine release from vesicles

Displaces norepinephrine from secretory vesicles leading to norepinephrine depletion

A 57-year-old man comes to the physician because of a 3-month history of fatigue, difficulty swallowing, and weight loss. He has smoked 1 pack of cigarettes daily for 30 years. He is 173 cm (5 ft 8 in) tall, and weighs 54 kg (120 lb); BMI is 18 kg/m2. Upper gastrointestinal endoscopy shows an exophytic tumor at the gastroesophageal junction. The patient is diagnosed with advanced esophageal adenocarcinoma. Palliative treatment is begun. Two months later, he complains of difficulty sleeping. His husband says that the patient does not get out of bed most days and has lost interest in seeing his friends. Mental status examination shows a blunted affect, slowed speech, and poor concentration. This patient is at increased risk of developing which of the following findings on polysomnography?

Increased periodic sharp-wave discharge

Increased slow-wave sleep-cycle duration

Increased spike-and-wave discharge

A 37-year-old male presents to general medical clinic reporting sleeping difficulties. He states that he has daytime sleepiness, having fallen asleep several times while driving his car recently. He sometimes experiences very vivid dreams just before awakening. You ask the patient's wife if she has witnessed any episodes where her husband lost all muscle tone and fell to the ground, and she confirms that he has not had this symptom. The patient notes that this condition runs in his family, and he desperately asks for treatment. You begin him on a first-line medication for this illness, which works by which mechanism of action?

Alpha-2 adrenergic receptor antagonism

An 8-year-old girl is brought to the physician by her parents for a 10-month history of disturbing dreams and daytime sleepiness. She has difficulty falling asleep and says she sometimes sees ghosts just before falling asleep at night. She has had a 7-kg (15-lb) weight gain during this period despite no changes in appetite. She is alert and oriented, and neurologic examination is unremarkable. During physical examination, she spontaneously collapses after the physician drops a heavy book, producing a loud noise. She remains conscious after the collapse. Polysomnography with electroencephalogram is most likely to show which of the following?

Decreased delta wave sleep duration

A 21-year-old man presents to the clinic complaining of feeling tired during the day. He is concerned as his grades in school have worsened and he does not want to lose his scholarship. Upon further questioning, the patient describes frequently experiencing a dreamlike state before falling asleep and after waking up. He also has frequent nighttime awakenings where he finds himself unable to move. He denies snoring. The patient does not drink alcohol or abuse any other drugs. The patient's BMI is 21 kg/m2, and his vital signs are all within normal limits. What is this patient's diagnosis?

Delayed sleep phase syndrome (DSPS)

Normal sleep physiology for USMLE Step 3: High-Yield Psychiatry Lessons

Sleep Architecture - The Building Blocks

Two main types: NREM (Non-Rapid Eye Movement) & REM (Rapid Eye Movement).
Sleep cycles through stages every 90-120 minutes, occurring 4-6 times per night.
NREM is divided into 3 stages (N1, N2, N3); REM is a single stage.

EEG waveforms for different sleep stages

⭐ REM sleep constitutes 20-25% of total sleep time, and REM periods lengthen as the night progresses.

NREM Sleep - Drifting Off Deep

EEG, EOG, and EMG Waveforms During Sleep Stages Accounts for ~75% of total sleep. Progresses from light to deep sleep, crucial for physical restoration. Characterized by ↓ heart rate, blood pressure, and respiration.

📌 Mnemonic: BATS Drink Blood (Theta, Spindles/K-complexes, Delta)

Stage N1 (~5%): Lightest sleep; transition from wakefulness.
- EEG: Theta waves.
Stage N2 (~45%): Intermediate depth sleep where bruxism can occur.
- EEG: Sleep spindles & K-complexes appear.
Stage N3 (~25%): Deep, slow-wave sleep (SWS).
- EEG: High-amplitude, low-frequency Delta waves.
- Site of parasomnias: sleepwalking, night terrors, bedwetting.

⭐ Stage N2 constitutes the largest percentage of total sleep time in a healthy adult.

REM Sleep - The Mind's Movie

EEG of REM sleep with sawtooth waves

"Paradoxical sleep": brain is highly active (beta waves) while the body is immobile.
EEG shows low-voltage, high-frequency activity similar to wakefulness, with characteristic "sawtooth waves."
Key Features:
- Rapid, conjugate eye movements.
- Atonia (skeletal muscle paralysis) prevents acting out dreams.
- Vivid, narrative-based dreaming.
Physiology: ↑ and variable heart rate/blood pressure, ↑ brain O₂ consumption, penile/clitoral tumescence.
Occurs every ~90 minutes; duration increases through the night.

⭐ Loss of atonia results in REM sleep behavior disorder, a strong predictor for α-synucleinopathies (e.g., Parkinson disease).

Sleep Regulation - The Master Clock

Suprachiasmatic Nucleus (SCN) in the hypothalamus acts as the master circadian pacemaker.
Receives light information from photosensitive ganglion cells in the retina via the retinohypothalamic tract.
Mechanism of Action:
- Light: Stimulates SCN → signals pineal gland → ↓ melatonin secretion → Wakefulness.
- Dark: No light stimulation → SCN allows pineal gland → ↑ melatonin secretion → Sleepiness.

⭐ SCN lesions (e.g., from a tumor or stroke) disrupt the timing of sleep, leading to an irregular sleep-wake cycle, but do not change the total amount of sleep per 24 hours.

Neurotransmitters - The Brain's Switches

Wake-Promoting ("ON"):
- Acetylcholine (ACh): Key for cortical arousal and initiating REM sleep.
- Monoamines: Norepinephrine (↑ vigilance), Dopamine (↑ motivation), Serotonin (complex role), Histamine.
- Orexin (Hypocretin): From lateral hypothalamus; stabilizes the awake state.
Sleep-Promoting ("OFF"):
- GABA: From ventrolateral preoptic nucleus (VLPO); inhibits wake-promoting centers.
- Adenosine: Accumulates with wakefulness, driving sleep pressure. Blocked by caffeine.
- Melatonin: Regulates circadian timing.

⭐ Loss of orexin-producing neurons in the lateral hypothalamus is the pathophysiologic basis for narcolepsy type 1.

High‑Yield Points - ⚡ Biggest Takeaways

NREM sleep has 3 stages; N3 (slow-wave sleep), with delta waves, is the most restorative.

Sleep spindles and K-complexes on EEG are pathognomonic for N2 sleep.

REM sleep features atonia, vivid dreaming, and an "awake" EEG with beta waves.

The suprachiasmatic nucleus (SCN) is the primary driver of the circadian rhythm.

Melatonin promotes sleep; acetylcholine is key for initiating REM sleep.

Aging leads to ↓ slow-wave sleep, ↓ REM latency, and ↑ sleep fragmentation.

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