Unit 4 – The Demand for Sleep: Core Vocabulary

A comprehensive set of vocabulary flashcards summarising key terms and definitions related to consciousness, sleep measurement, circadian regulation and lifespan changes in sleep, aligned with Unit 4: The Demand for Sleep.

Psychological Construct

An abstract concept used to describe processes (e.g., consciousness, sleep) that cannot be observed or measured directly.

Consciousness

Our personal awareness of internal thoughts and feelings and the external environment at any given moment.

Normal Waking Consciousness (NWC)

A state of clear, organised awareness when we are awake and attentive to internal and external stimuli.

Altered State of Consciousness (ASC)

Any condition of awareness distinctly different from NWC, either naturally occurring (e.g., sleep) or deliberately induced (e.g., meditation, drug use).

Sleep

A reversible, naturally occurring ASC marked by reduced responsiveness to external stimuli and characteristic physiological patterns.

REM Sleep

Rapid-eye-movement sleep featuring beta-like brain waves, vivid dreaming, and muscle paralysis; known as ‘paradoxical sleep.’

NREM Sleep

Non-rapid-eye-movement sleep comprising stages 1–3, characterised by reduced physiological activity and gradual progression to deep sleep.

Stage 1 NREM

Light sleep lasting 5–10 min with alpha→theta wave transition, slow eye-rolling and possible hypnic jerks.

Stage 2 NREM

Light sleep (~20 min first cycle) dominated by theta waves; forms ~50 % of total sleep time.

Stage 3 NREM (Slow-Wave Sleep)

Deep sleep with >50 % delta waves, very low responsiveness, and possible sleepwalking/talking.

Paradoxical Sleep

Another term for REM sleep, highlighting active brain activity alongside muscle paralysis.

Sleep Cycle

An ultradian pattern (~90 min) of NREM and REM stages repeated 4–6 times per night.

Ultradian Rhythm

A biological cycle shorter than 24 h, such as the NREM–REM sleep cycle or heartbeat.

Circadian Rhythm

A 24-hour biological cycle regulating processes like the sleep–wake pattern and body temperature.

Suprachiasmatic Nucleus (SCN)

A tiny hypothalamic ‘master clock’ that receives light signals and coordinates circadian rhythms.

Melatonin

A hormone released by the pineal gland in dim light, promoting drowsiness and regulating sleep timing.

Zeitgeber

An external cue (e.g., light) that synchronises the body’s internal clock to the environment.

Blue Light

High-frequency light that suppresses melatonin release and can delay sleep onset.

Electroencephalograph (EEG)

Device that detects, amplifies and records electrical activity of the brain as brain-waves.

Electromyograph (EMG)

Device that detects, amplifies and records electrical activity of skeletal muscles.

Electro-oculograph (EOG)

Device that detects, amplifies and records electrical activity of muscles controlling eye movement.

Objective Measure

A data-collection method free from personal bias, e.g., EEG, EMG, EOG.

Subjective Measure

Data based on personal opinion or self-report, such as sleep diaries and video monitoring.

Sleep Diary

A self-report log where individuals record bedtime, awakenings, dreams, and daily habits affecting sleep.

Video Monitoring

Recorded observation of sleepers to identify behaviours like sleepwalking or breathing difficulties.

Beta Waves

High-frequency, low-amplitude EEG waves linked to alert wakefulness and REM sleep.

Alpha Waves

Moderate-frequency, low-amplitude waves typical of relaxed wakefulness and Stage 1 NREM.

Theta Waves

Medium-frequency waves with mixed amplitude, dominant in Stage 2 and early Stage 3 NREM.

Delta Waves

Low-frequency, high-amplitude waves characteristic of deep Stage 3 NREM sleep.

Hypnic Jerk

An involuntary muscle twitch occurring during Stage 1 NREM, often accompanied by a falling sensation.

Sleep Paralysis

Loss of voluntary muscle movement during REM sleep, preventing physical acting-out of dreams.

Hypnogram

A graph displaying the progression of sleep stages across the night’s ultradian cycles.

Sleep Pressure

The increasing drive for sleep that builds during wakefulness and dissipates during sleep.

Adolescent Sleep Phase Delay

Biological shift where melatonin release occurs ~2 h later, causing later sleep onset and wake time.

Advanced Sleep Phase (Elderly)

A circadian shift causing earlier evening sleepiness and earlier morning awakening in older adults.

Sleep–Wake Cycle

The 24-hour pattern of alternating sleep and wake states; a circadian rhythm.

Endogenous Rhythm

A biological cycle generated internally, persisting without external cues (e.g., SCN-controlled sleep–wake cycle).

Saw-Tooth Waves

Distinctive rapid, jagged EEG pattern often seen during REM sleep.

Growth Hormone

Hormone released mainly in deep NREM sleep, vital for physical growth and tissue repair.

Sleep Fragmentation

Frequent awakenings or arousals that interrupt consolidated sleep, common in the elderly.

Night Mode

Device setting that shifts screen light toward warmer tones, reducing blue-light exposure before sleep.

Sleep Across the Lifespan

Trend where total sleep time and REM proportion decrease from infancy to old age, with deep NREM diminishing markedly.

Stage 1 Newborn REM Onset

In the first weeks of life, infants often enter sleep through REM rather than NREM Stage 1.

Slow-Wave Sleep Loss (Ageing)

Progressive reduction of Stage 3 NREM in adults, often absent in very elderly sleepers.

Sleep Quality

A subjective and objective assessment of how restorative and uninterrupted a sleep episode is (often gauged by proportion of deep sleep).

Sleep Quantity

The total duration of a sleep episode, typically measured in hours.

DARE (Detect, Amplify, Record Electrical)

Mnemonic summarising the functions of EEG, EMG, and EOG devices.

Sensorimotor Development (REM Twitches)

Hypothesis that muscle twitches during infant REM foster neural connections for coordinated movement.

Biological Clock Drift

Tendency for the endogenous circadian period to lengthen (~25 h) without external light cues.

Sleep Onset

Transition from wakefulness to sleep, usually via Stage 1 NREM in mature sleepers.