15. Sleep and Sleep Disorders

Why is sleep essential for human function?

It maintains homeostasis and supports alertness, performance, and health.

What happens after just one night of sleep deprivation?

Vigilance and performance on monotonous tasks deteriorate.

What are the four major proposed functions of sleep?

Restoration/recovery, energy conservation, predator avoidance, memory modulation.

How does sleep aid in restoration?

By reversing or restoring degraded biochemical/physiological processes.

How does sleep conserve energy?

By reducing metabolic rate and body temperature in endothermic animals.

How does sleep promote predator avoidance?

By inhibiting motor activity to reduce predator attention.

How does sleep affect memory?

It may erase undesirable neuronal activity or promote memory consolidation.

What are the two main categories of sleep stages?

Non-REM (NREM) and REM.

What happens to REM and N3 sleep with age?

They both decrease.

What EEG pattern is seen when awake with eyes open?

Beta waves (>13 Hz).

What EEG pattern is seen when awake with eyes closed?

Alpha waves (8–13 Hz).

What EEG pattern is seen in N1 sleep?

Theta waves (4–8 Hz).

What EEG features define N2 sleep?

Sleep spindles (12–14 Hz) and K-complexes (0.5 Hz).

What EEG pattern defines N3 sleep?

Delta waves (0–4 Hz), also called slow-wave sleep.

What are parasomnias associated with N3 sleep?

Sleepwalking, bedwetting, night terrors.

What EEG pattern defines REM sleep?

A mix of all frequencies.

What happens to muscle activity during REM sleep?

Muscle atonia (paralysis).

What happens to eye movements in REM sleep?

Rapid eye movements.

What brain structure regulates the circadian cycle?

Suprachiasmatic nucleus (SCN) of the hypothalamus.

What synchronizes the SCN to the environment?

Light input from the retina.

When is the SCN most active?

During the daytime.

What hormone does the pineal gland release at night?

Melatonin.

What is the role of melatonin?

Acts as a circadian signal to the body.

What is the overall purpose of the circadian system?

To adaptively schedule activity and metabolism based on environmental light and temperature.

What is the pattern of sleep in diurnal species like humans?

Active during the day, sleep at night.

What is the definition of insomnia?

Difficulty initiating or maintaining sleep despite adequate opportunity, with daytime dysfunction.

How often must symptoms occur to diagnose insomnia?

At least 3 times per week.

What is the difference between short-term and chronic insomnia?

Short-term <3 months; chronic ≥3 months.

What are common secondary causes of insomnia?

Mood disorders, substance use, medical conditions.

What is the first-line treatment for insomnia?

Cognitive behavioral therapy for insomnia (CBT-I).

What are components of CBT-I?

Sleep hygiene, stimulus control, sleep restriction, relaxation therapy.

When are medications used for insomnia?

Short-term, alongside CBT-I.

What class of drugs is commonly used for insomnia?

Benzodiazepines and non-benzo receptor agonists (e.g., zolpidem).

How do sedative hypnotics work in insomnia?

Activate GABA receptors.

What are two alternative pharmacologic treatments for insomnia?

Ramelteon (melatonin agonist), Suvorexant (dual orexin receptor antagonist).

What is hypersomnia?

Excessive daytime sleepiness despite adequate nighttime sleep.

What symptoms accompany hypersomnia?

Fatigue, reduced concentration, memory problems.

What are the two major types of hypersomnia?

Narcolepsy and idiopathic hypersomnia.

What is the hallmark of narcolepsy?

Rapid transition from wakefulness to REM sleep.

What other nighttime symptom is common in narcolepsy?

Disrupted or fragmented sleep.

What causes narcolepsy?

Loss of orexin-producing neurons in the hypothalamus.

What are the core features of narcolepsy?

Hypnagogic/hypnopompic hallucinations, cataplexy, sleep paralysis.

What is idiopathic hypersomnia?

Excessive sleepiness despite >11 hours of sleep per day.

What medications treat excessive daytime sleepiness?

Methylphenidate, modafinil, solriamfetol, pitolisant, sodium oxybate.

What medications treat cataplexy?

Sodium oxybate, pitolisant, SSRIs.

What defines a sleep-related breathing disorder?

Impaired respiration during sleep with daytime dysfunction.

What are the three major types of sleep-related breathing disorders?

Obstructive sleep apnea (OSA), central sleep apnea (CSA), and obesity hypoventilation syndrome.

How is obstructive sleep apnea (OSA) diagnosed?

5 obstructive apneas or hypopneas per hour on polysomnography.

What are risk factors for OSA?

Obesity, oropharyngeal anatomy, genetics, alcohol or sedative use.

What are consequences of untreated OSA?

Cognitive and cardiovascular dysfunction.

What is central sleep apnea (CSA)?

5 central apneas per hour due to impaired CO₂ detection and respiratory drive.

What are common causes of CSA?

Congestive heart failure, opioid use, brainstem dysfunction.

What is obesity hypoventilation syndrome?

Chronic CO₂ retention due to OSA and obesity.

How is obesity hypoventilation diagnosed?

Elevated serum bicarbonate and/or elevated CO₂ during sleep study.

What symptoms are associated with obesity hypoventilation syndrome?

Morning headaches, fatigue, daytime sleepiness.

What is the first-line treatment for sleep-related breathing disorders?

Continuous positive airway pressure (CPAP).

What other treatments may help in sleep-related breathing disorders?

Supplemental oxygen, treating CHF or stopping opioids, and weight loss.

What are parasomnias?

Excessive movements or behaviors during sleep of unclear cause.

During which sleep stages can parasomnias occur?

NREM or REM sleep.

What are two types of NREM parasomnias?

Sleepwalking and sleep terrors.

What is the typical age range for NREM parasomnias?

4–12 years old.

What are features of sleepwalking?

Amnesia for the event, difficulty waking, may be triggered by stimulants.

How are NREM parasomnias diagnosed?

Usually clinically, but can be confirmed by polysomnography.

What are features of sleep terrors?

Sudden arousal with panic or screaming, autonomic activation, amnesia of event.

What may cause NREM sleep terrors?

Genetics or certain medications.

What is REM sleep behavior disorder (RBD)?

Acting out dreams due to loss of REM-induced atonia.

What conditions are associated with RBD?

Parkinson’s disease and dementia with Lewy bodies.

How is RBD diagnosed?

Polysomnography showing lack of REM atonia.

What is nightmare disorder?

Frightening dreams that awaken the person and are often remembered.

What psychiatric conditions may be associated with nightmare disorder?

PTSD or acute stress.

Which medications can trigger RBD or nightmares?

Antidepressants and untreated OSA.

How are NREM parasomnias treated?

Reassurance, safe sleep environment, remove triggers, low-dose benzodiazepines.

How is RBD treated?

Safe sleep environment, remove triggers, treat OSA or psychiatric illness, high-dose melatonin.

What is restless leg syndrome (RLS)?

An urge to move the legs at night before sleep, relieved by movement.

How does RLS affect sleep?

It impairs the ability to fall asleep.

What deficiency is often associated with RLS?

Iron deficiency.

Which substances can worsen RLS?

Caffeine, alcohol, antidepressants, dopamine antagonists.

What is the first-line treatment for RLS?

Correct iron deficiency.

What should be done with triggering substances in RLS?

Remove or reduce them.

What medication may help if RLS is persistent?

Gabapentin.