A
- Adenosine
- A chemical that builds up in the brain during waking hours, creating "sleep pressure." Caffeine works by blocking adenosine receptors.
- Apnea
- A temporary pause in breathing during sleep. See Sleep Apnea.
B
- Blue Light
- Light in the 450-495 nanometer wavelength range. Blue light suppresses melatonin production more than other wavelengths, which can affect sleep timing when exposed in the evening.
C
- Circadian Rhythm
- The body's internal 24-hour clock that regulates sleep-wake cycles, hormone release, body temperature, and other biological processes. It's primarily influenced by light exposure.
- Chronotype
- An individual's natural preference for sleep timing. Common types include "morning larks" (early risers) and "night owls" (late sleepers).
- CBT-I (Cognitive Behavioral Therapy for Insomnia)
- A structured program that helps identify and replace thoughts and behaviors causing sleep problems. Often considered the first-line treatment for chronic insomnia.
D
- Deep Sleep
- Also called slow-wave sleep (SWS) or N3 sleep. The most restorative sleep stage, important for physical recovery, immune function, and memory consolidation.
H
- Hypnogram
- A graph that shows the progression through different sleep stages over the course of a night.
- Hypersomnia
- A condition characterized by excessive daytime sleepiness or prolonged nighttime sleep.
I
- Insomnia
- A sleep disorder characterized by difficulty falling asleep, staying asleep, or both, despite adequate opportunity for sleep. Can be acute (short-term) or chronic.
L
- Light Sleep
- The transitional stages of sleep (N1 and N2) between wakefulness and deep sleep. Easier to wake from than deep sleep.
- Lux
- A unit measuring light intensity. Bright daylight is 10,000-100,000 lux; indoor lighting is typically 100-500 lux; moonlight is about 1 lux.
M
- Melatonin
- A hormone produced by the pineal gland that signals darkness to the body and helps regulate sleep timing. Production is suppressed by light exposure.
- Microsleep
- Brief, involuntary episodes of sleep lasting a few seconds, often occurring during sleep deprivation. Dangerous when driving or operating machinery.
N
- NREM Sleep
- Non-Rapid Eye Movement sleep. Comprises three stages (N1, N2, N3) and makes up about 75-80% of total sleep time.
- Nocturia
- The need to wake up during the night to urinate. A common cause of sleep fragmentation.
P
- Polysomnography
- A comprehensive sleep study that records brain waves, blood oxygen levels, heart rate, breathing, and eye/leg movements during sleep.
R
- REM Sleep
- Rapid Eye Movement sleep. A sleep stage characterized by vivid dreams, rapid eye movements, and temporary muscle paralysis. Important for cognitive function, memory, and emotional processing.
- REM Rebound
- An increase in REM sleep following a period of REM deprivation, such as after stopping alcohol or certain medications.
S
- Sleep Architecture
- The structure and pattern of sleep cycles and stages throughout the night.
- Sleep Apnea
- A disorder characterized by repeated breathing interruptions during sleep. Can be obstructive (airway blockage) or central (brain signaling issue).
- Sleep Cycle
- A complete sequence through all sleep stages, lasting approximately 90 minutes. Adults typically experience 4-6 cycles per night.
- Sleep Debt
- The cumulative effect of not getting enough sleep. While some recovery is possible, chronic sleep debt cannot be fully "repaid."
- Sleep Hygiene
- Habits and environmental factors that promote consistent, quality sleep. Includes consistent schedules, bedroom optimization, and pre-sleep routines.
- Sleep Latency
- The time it takes to fall asleep after getting into bed. Normal sleep latency is typically 10-20 minutes.
- Sleep Pressure
- The biological drive to sleep that builds during waking hours, primarily due to adenosine accumulation.
- Slow-Wave Sleep
- See Deep Sleep.
- Suprachiasmatic Nucleus (SCN)
- The "master clock" in the brain's hypothalamus that controls circadian rhythms. Receives direct input from the eyes about light exposure.