Lesson 5 – Sleep and Dreams Vocabulary

A comprehensive set of vocabulary flashcards covering key terms, structures, stages, theories, and disorders discussed in Lesson 5 on Sleep and Dreams.

Sleep

A natural, periodic state of rest in which consciousness of the external world is suspended.

Repair Theory

The idea that sleep restores, replenishes, and rebuilds the brain and body.

Ecological (Evolutionary) Theory

View that sleep evolved to conserve energy and keep organisms out of harm during times of day to which they are poorly adapted.

Sleep-Memory Consolidation

Process by which sleep strengthens useful neural connections and weeds out unneeded ones, enhancing learning and problem solving.

Biological Rhythm

Regular, cyclic change in a bodily process (e.g., circadian rhythm).

Circadian Rhythm

Endogenous cycle of about 24 h regulating body temperature, hormone release, sleep–wake patterns, etc.

Endogenous Cycle

A self-generated biological rhythm that persists without external cues.

Circannual Rhythm

Yearly endogenous cycle such as animal migration or hibernation.

Free-Running Rhythm

Circadian rhythm that persists at its own period (slightly >24 h) without time cues.

Zeitgeber

External stimulus (light, noise, temperature, exercise) that resets the biological clock.

Jet Lag

Misalignment of internal circadian clock with new time zones, causing daytime sleepiness and nighttime insomnia.

Phase-Delay

Shift in circadian rhythm caused by staying awake later (common when traveling west).

Phase-Advance

Shift in circadian rhythm caused by going to bed and rising earlier (common when traveling east).

Shift Work Problem

Difficulty sleeping deeply during daylight; night-shift workers often remain groggy and accident-prone.

Suprachiasmatic Nucleus (SCN)

Cluster of cells in the hypothalamus above the optic chiasm that is the master clock for circadian rhythms.

Retinohypothalamic Path

Optic-nerve branch carrying light information directly from retina to SCN to reset the clock.

Pineal Gland

Endocrine gland posterior to the thalamus that secretes melatonin.

Melatonin

Hormone that increases sleepiness; secretion rises a few hours before usual bedtime.

Beta Waves

Short, fast EEG waves seen when awake and alert.

Alpha Waves

Larger, slower EEG waves present during relaxed wakefulness just before sleep.

Stage 1 Sleep

Light sleep with small, irregular EEG waves; brain activity begins to decline.

Stage 2 Sleep

Sleep stage marked by sleep spindles (12–14 Hz bursts) and K-complexes (sharp negative/positive waves).

Sleep Spindle

Brief 12–14 Hz burst in Stage 2 indicating inhibited sensory processing.

K-Complex

High-amplitude negative wave followed by small positive wave in Stage 2 sleep.

Stage 3 Sleep

Beginning of slow-wave sleep with some delta waves.

Stage 4 Sleep

Deepest slow-wave sleep characterized by almost pure delta waves.

Slow-Wave Sleep (SWS)

Combined Stages 3 & 4; slow, large-amplitude EEG, low heart/breathing rate, synchronized neurons.

REM Sleep

Rapid-eye-movement stage after cycling back; EEG resembles wakefulness, vivid dreaming common.

Non-REM (NREM) Sleep

Collective term for Stages 1-4, excluding REM.

Electroencephalograph (EEG)

Instrument that records brain’s electrical activity and revealed distinct sleep stages.

Cognitive Theory of Dreaming

Idea that REM sleep discards useless connections and forms remote associations, consolidating memory.

Activation-Synthesis Hypothesis

Dream theory stating spontaneous pons activity activates cortex, which synthesizes a story.

PGO Waves

Pons–geniculate–occipital bursts linked to REM dreams’ visual imagery.

Clinico-Anatomical Hypothesis

Theory viewing dreams as thinking under reduced sensory input and diminished prefrontal control.

Hippocampus (during sleep)

Active region forming memories and replaying daily events.

Reticular Formation

Midbrain structure that toggles between arousal and sleep.

Pontomesencephalon

Part of reticular formation; ACh & glutamate neurons that increase cortical arousal; stimulation awakens sleeper.

Locus Coeruleus

Pons nucleus releasing norepinephrine; boosts alertness, suppresses REM, dormant during sleep.

Basal Forebrain

Region anterior to hypothalamus; GABA neurons induce sleep, ACh neurons increase arousal and shift NREM→REM.

Histamine (Hypothalamus)

Neurotransmitter from posterior hypothalamus that promotes wakefulness.

Dorsal Raphe Nuclei

Serotonin-releasing midbrain nuclei that interrupt or shorten REM sleep.

Sleep Deprivation Effects

Impaired routine tasks (<48 h), possible psychosis, anxiety, hallucinations, mood swings with REM loss.

Somnambulism

Sleepwalking occurring during Stage 4 when dreaming is least likely.

Nightmare

Disturbing dream experienced during REM sleep.

Night Terror

Sudden arousal with panic (screaming, racing heart) during Stage 3 or 4 NREM.

Narcolepsy

Disorder with sudden sleep attacks, cataplexy, sleep paralysis, and hypnagogic hallucinations (REM intrusions).

Cataplexy

Sudden muscle weakness triggered by emotion, common in narcolepsy.

Sleep Paralysis

Temporary inability to move when falling asleep or waking, often seen in narcolepsy.

Hypnagogic Hallucination

Vivid dreamlike perception that blurs with reality at sleep onset, linked to narcolepsy.

Insomnia

Chronic difficulty falling or staying asleep, leading to inadequate rest.

Sleep Apnea

Disorder of prolonged breathing pauses during sleep causing daytime sleepiness and health risks.

Periodic Limb Movement Disorder

Involuntary leg movements during NREM; legs kick for minutes to hours.