Sleep: The body's rest cycle.
Sleep is triggered by a complex group of hormones that are active in the main, and that respond to cues from the body itself and the environment. About 80 percent of sleep is dreamless, and is known as non-rapid eye movement (NREM) sleep.
During NREM sleep, the breathing and heart rate are slow and regular, the blood pressure is low, and the sleeper is relatively still. NREM sleep is divided into four stages of increasing depth of sleep: Level 1 sleep is a transition period between sleep and wakefulness; Level 2 sleep features significant slowing of heartbeat and breathing, and makes up about 50 percent of all sleep; and Level 3 and 4 (Delta) sleep are marked by very slow respiration and heartbeat. Level 4 sleep leads to rapid eye movement (REM) sleep, also known as Level 5 sleep.
Dreams occur during three to five periods of REM sleep each night. REM sleep occurs at intervals of one to two hours, and is variable in length. REM sleep is characterized by irregular breathing and heart rate, and involuntary muscle jerks.
Most adults need around eight hours of sleep on a regular schedule to function well, although some require less, and others more. (It has been said that men need an hour less sleep than women.) Children, particularly teenagers, often need nine or ten hours for optimal functioning.
Sleep disorders include a range of problems -- from insomnia to narcolepsy -- and affect millions of Americans. Here you'll find in-depth sleep apnea information ...
Nonprofit organization supporting public education, sleep-related research, and advocacy related to sleep deprivation, sleep disorders, and excessive sleepiness ...
Abstracts and full research articles published in SLEEP, the official journal of the APSS. Sleep and sleep disorder scientific findings.
Fact sheet on normal sleep and sleep disorders developed by the National Institute of Neurological Disorders and Stroke (NINDS).
Read about how to get a good nights sleep. Sleep problems such as sleep apnea, sleep deprivation, insomnia, restless leg syndrome, snoring, sleepwalking, and more are ...