Glossary

Circadian Rhythms: cyclical changes, like fluctuations in body temperature, hormone levels, and sleep that occur over a 24-hour period, driven by the body's biological “clock”

Cortisol: one of several stress hormones produced by the adrenal cortex that is secreted near the end of sleep to stimulate alertness

GABA: short for gamma-aminobutyric acid, an amino acid in the central nervous system associated with the transmission of nerve impulses

Homeostasis: the process by which the body maintains a “steady state” of internal conditions such as blood pressure, body temperature, acid-base balance, and sleep

Hypothalamus: region of the forebrain below the thalamus, controlling body temperature, thirst, and hunger, and involved in sleep and emotional activity

Insomnia: sleep disorder characterized by an inability to sleep or to remain asleep for a reasonable period or waking not feeling refreshed

Melatonin: hormone secreted by the pineal gland especially in response to darkness that promotes sleep

Narcolepsy: a sleep disorder characterized by sudden and uncontrollable episodes of deep sleep

Non-Rapid Eye Movement (NREM) Sleep: one of four initial sleep stages preceding REM sleep characterized by a reduction in physiological activity and a slowing of brain waves

Parasomnia: a category of sleep disorders in which abnormal physiological or behavioral events occur during sleep, including night terrors and sleepwalking

Pineal Gland: a small cone-shaped organ of the brain that secretes the hormone melatonin into the bloodstream Receptor: a molecular structure within a cell or on the surface characterized by selective binding of a specific substance and a specific physiologic effect that accompanies the binding

Rapid Eye Movement (REM) Sleep: a recurring sleep state characterized by rapid eye movement and intense brain activity, during which dreaming occurs

Relaxation Therapy: a form of sleep behavioral therapy including muscle relaxation, biofeedback, meditation, and breathing techniques aimed at helping the patient fall asleep faster and stay asleep longer

Restless Legs Syndrome: a sleep disorder characterized by leg discomfort during sleep, which is only relieved by frequent movements of the legs

Sleep: a natural and periodic state of rest during which consciousness of the environment is suspended

Sleep Apnea: a serious, potentially life-threatening sleep disorder characterized by episodes of interrupted breathing during sleep

Sleep Architecture: the predictable pattern of alternating REM and NREM sleep that occurs throughout the night, consisting of four NREM phases and one REM phase

Sleep Hygiene: practices conducive to good sleep including maintaining the same sleep and wake patterns every day, avoiding stimulants late in the day, ensuring adequate exposure to natural daylight, and maintaining a cool, dark, and quiet sleep environment

Sleep-Restriction Therapy: a form of sleep behavioral therapy that restricts the individual's time in bed, resulting in sleep deprivation that allows the individual to fall asleep

Sleep-Wake Cycle: the biological pattern of alternating sleep and wakefulness, in humans roughly 8 hours of nocturnal sleep and 16 hours of daytime activity

Stimulus-Control Therapy: a form of sleep behavioral therapy that conditions the patient to associate the bed and bedroom with sleep

Suprachiasmatic Nucleus (SCN): a region in the hypothalamus that regulates circadian rhythms, acting as the body's sleep-wake center or “biological clock”