The Demand for Sleep – Key Vocabulary

A set of key vocabulary flashcards covering concepts, physiological measures, biological rhythms and lifespan changes related to sleep.

Psychological Construct

An agreed-upon concept used to describe a phenomenon that cannot be directly observed, such as consciousness or sleep.

Consciousness

Our level of awareness of internal thoughts and feelings and external stimuli at any given moment.

Normal Waking Consciousness (NWC)

The state of being awake and aware of internal and external stimuli, able to direct attention and regulate thoughts, emotions and behaviour.

Altered State of Consciousness (ASC)

Any state that differs noticeably from NWC in level of awareness, including day-dreaming, meditation, sleep or drug-induced states.

Sleep

A naturally occurring altered state of consciousness marked by reduced awareness, disengagement from the environment and characteristic physiological changes.

Sleep Episode

The full period spent asleep, consisting of several repeated sleep cycles of REM and NREM sleep.

Sleep Cycle

A roughly 90-minute pattern in which a sleeper progresses through NREM stages 1–3 and REM sleep.

REM Sleep

Rapid-eye-movement sleep with high brain activity, vivid dreaming and muscle paralysis; 20–25 % of sleep in adults.

Paradoxical Sleep

Another term for REM sleep describing the combination of an active brain and an inactive body.

NREM Sleep

Non-rapid-eye-movement sleep comprising Stages 1–3; about 75–80 % of adult sleep.

NREM Stage 1 (N1)

Light sleep lasting ~5 min with slow rolling eye movements and hypnic jerks; low arousal threshold.

NREM Stage 2 (N2)

Light–moderate sleep featuring sleep spindles, further slowing of body functions and higher arousal threshold than N1.

NREM Stage 3 (N3)

Deep or slow-wave sleep dominated by delta waves, high arousal threshold and possible sleep inertia on waking.

Sleep Inertia

The groggy, disoriented feeling experienced immediately after awakening from deep sleep.

Hypnic Jerk

An involuntary muscle twitch that often occurs as a person is drifting into sleep, typically during N1.

Electroencephalograph (EEG)

A device that detects, amplifies and records electrical activity of the brain to produce brain-wave patterns.

Electromyograph (EMG)

A device that detects, amplifies and records electrical activity of skeletal muscles to indicate muscle tone.

Electro-oculograph (EOG)

A device that detects, amplifies and records electrical activity of the muscles controlling eye movements.

Sleep Diary

A self-reported log of sleeping and waking times, awakenings and perceived sleep quality kept over several days or weeks.

Video Monitoring

The use of cameras and microphones to record a person while asleep, often to study sleep behaviours or disorders.

Beta Waves

High-frequency, low-amplitude EEG waves associated with alertness and active mental activity.

Alpha Waves

Moderate-frequency, low-amplitude EEG waves present during relaxed wakefulness with eyes closed.

Theta Waves

Lower-frequency, higher-amplitude EEG waves typical of light sleep (N1–N2).

Delta Waves

Low-frequency, high-amplitude EEG waves characteristic of deep sleep (N3).

Biological Rhythm

A regularly recurring physiological process regulated by internal mechanisms, such as the sleep-wake cycle.

Circadian Rhythm

A biological rhythm lasting about 24 hours, e.g. the sleep-wake cycle.

Ultradian Rhythm

A biological rhythm shorter than 24 hours, such as the 90-minute sleep cycle.

Sleep-Wake Cycle

The daily pattern of alternating sleep and wakefulness, a circadian rhythm.

Suprachiasmatic Nucleus (SCN)

A pair of cell clusters in the hypothalamus acting as the brain’s master biological clock regulating circadian rhythms.

Melatonin

A hormone released by the pineal gland in darkness; promotes drowsiness and regulates the sleep-wake cycle.

Cortisol

An adrenal hormone that elevates alertness and peaks in the morning to promote wakefulness.

Free-Running Rhythm

A circadian rhythm that operates without external time cues, typically drifting to about 24.2–25 hours.

Sleep-Wake Cycle Shift (Adolescence)

A 1–2 hour biological delay in sleep onset during adolescence, often causing later bedtimes and wake times.

Advanced Sleep Phase Syndrome

A forward shift in the sleep-wake cycle common in older adults, leading to earlier sleep and wake times.

Psychological Changes (Consciousness)

Alterations in awareness, cognition, emotion, self-control and perception that distinguish different states of consciousness.

Physiological Changes (Consciousness)

Body changes such as brain-wave patterns, heart rate and eye movements associated with different consciousness states.

Objective Data

Information obtained through direct measurement or observation, independent of the observer’s interpretation.

Subjective Data

Self-reported information based on personal perceptions, feelings or opinions.

Quantitative Data

Numerical information that can be statistically analysed, e.g. minutes of REM sleep.

Qualitative Data

Descriptive information that provides context or detail, e.g. a participant’s dream narrative.

Sleep Across the Lifespan

The systematic changes in total sleep time, REM/NREM proportions and timing from infancy to old age.

Neonatal Sleep

Sleep pattern of newborns (0–15 days): ~16 h sleep with 50 % REM and 50 % NREM.

Infant Sleep

Sleep of 3–24 month olds: ~13.5 h sleep with ~35 % REM and 65 % NREM.

Childhood Sleep

Sleep of 2–14 year olds: ~10–11 h sleep; REM falls to ~20 %, NREM rises to ~80 %.

Adolescent Sleep

Sleep of 14–18 year olds: ~9 h total with 20 % REM; features delayed sleep onset.

Young Adult Sleep

Sleep of 18–30 year olds: ~7.75 h total; stable 20 % REM and 80 % NREM.

Middle Adult Sleep

Sleep of 30–75 year olds: ~7–8 h with consistent REM/NREM proportions.

Old Age Sleep

Sleep of 75 + year olds: ~6 h, frequent awakenings, reduced deep NREM (stage 3) and advanced sleep phase.

Sleep Spindle

A brief burst of high-frequency brain activity occurring during NREM Stage 2, linked to memory consolidation.

Sleep Study Unit

A laboratory setting equipped to record physiological measures while participants sleep.

Muscle Atonia

The near-paralysis of skeletal muscles during REM sleep that prevents acting out dreams.