The recurring period of relative physical and psychological disengagement from one’s environment accompanied by characteristic electroencephalogram (EEG) findings and divisible into two categories: non–rapid eye movement (NREM) sleep, also known as orthodox or synchronized (S) sleep; and rapid eye movement (REM) sleep, also referred to as paradoxical or desynchronized (D) sleep. Dreaming sleep is another, although less accurate, term for REM sleep. Four stages of NREM sleep based on EEG findings are Stage 1, occurring immediately after sleep begins, with a pattern of low amplitude and fast frequency; Stage 2, having characteristic waves of 12–16 cycles per second, known as sleep spindles; and Stages 3 and 4, having progressive further slowing of frequency and increase in amplitude of the wave forms.
Over a period of 90 minutes after the beginning of sleep, a person has progressed through the four stages of NREM sleep and emerges from them into the first period of REM sleep. REM sleep is associated with dreaming, and brief cycles (20–30 minutes) of this sleep recur about every 90 minutes throughout the night. Coordinated rapid eye movements give this type of sleep its name. Sleep patterns vary with age, state of health, medication, and psychological state.
The state or a period of resting, usually at night, when the eyes are closed and you are not conscious of what is happening.
State of reduced consciousness and depressed metabolism occurring normally at regular intervals, ranging from as much as 20 hours a day in some infants to as little as 5 or 6 hours a day in some adults, esp. the aged. Sleep can be divided into two parts: nonrapid eye movement sleep, representing about 75% of total sleep, during which dreaming does not occur; and rapid eye movement sleep, during which dreaming does occur.
The body’s rest cycle, including a state of natural unconsciousness. Sleep is characterized by a mostly unmoving body posture and diminished sensitivity to external stimuli. Sleep is triggered by complex hormonal activity that responds to cues from the body and the environment. The sleep- wake cycle is controlled by the body’s internal clock.
A state of natural unconsciousness, during which the brain’s activity is not apparent (apart from the continued maintenance of basic bodily functions, such as breathing) but can be detected by means of an electroencephalogram (EEG). Different stages of sleep are recognized by different EEG wave patterns. Drowsiness is marked by short irregular waves; as sleep deepens the waves become slower, larger, and more irregular. This slow-wave sleep is periodically interrupted by episodes of paradoxical, or REM (rapid-eye-movement), sleep, when the EEG pattern is similar to that of an awake and alert person. Dreaming occurs during REM sleep. The two states of sleep alternate in cycles of from 30 to 90 minutes, REM sleep constituting about a quarter of the total sleeping time.
Sleep is a state which alternates with wakefulness, and in which awareness and responsiveness to the environment are reduced. It is not, however, uniform and can be divided into two main states, differentiated according to electrical recordings of brain activity (EEG), of the muscles (EMG), and of the eye movements (EOG).
A periodic state of rest accompanied by varying degrees of unconsciousness and relative inactivity. Although sleep is thought of as something that occurs once each 24-hr period, at least half of the world’s population has an afternoon nap or siesta as part of their lifelong sleep-wake pattern. The need for and value of sleep is obvious, yet the explanation of why it is so effective in providing a daily renewal of a feeling of health and well-being is lacking.
A inherent condition of diminished consciousness and decreased metabolism, sleep constitutes approximately one third of an average lifespan.
EEG recordings that capture the brain’s electrical patterns while sleeping reveal the presence of two distinct sleep phases: REM (rapid eye movement) and NREM (non-rapid eye movement). These phases alternate in cycles spanning roughly 90 minutes during the entire sleep duration. NREM sleep, constituting the majority of the sleep period, commences with a state of drowsiness. As time progresses, brain waves transition into deeper and slower patterns, eventually leading to the lowest levels of brain activity and metabolism. Dreams are rare during this phase.
During REM sleep, there’s a sudden surge in brain activity accompanied by elevated temperature and increased blood flow. Rapid eye movements and dreaming take place. This phase, also referred to as paradoxical sleep, intermittently breaks the sequence of NREM sleep. The initial REM cycle typically occurs 90 to 100 minutes after sleep initiation, lasting around five to 10 minutes. As the sleep duration progresses, the duration of REM sleep intervals extends. The final REM sleep period of a night’s sleep, among the four or five cycles, can endure for approximately an hour.
Sleep is an essential requirement for humans, evident from the adverse outcomes of sleep deprivation. Despite this, the precise manner in which sleep proves advantageous remains unclear.
The necessity for sleep diminishes as individuals age. A one-year-old baby typically requires around 14 hours of nightly sleep, while a five-year-old child needs approximately 12 hours. Adults, on average, find seven to eight hours sufficient for sleep. (Yet, some adults may require over 10 hours, while others can function well with five hours or less.) The elderly generally sleep less during the night compared to young adults but may take naps during the day.
Sleep disorders are categorized into four primary groups: challenges with initiating or maintaining sleep, struggles with staying alert, disturbances to the sleep-wake cycle (like those caused by shift work or crossing time zones), and various other issues such as nocturnal enuresis, night terrors, or somnambulism.
A time when bodily activities slow down and one enters a state of semi-awareness; a routine, natural pause that allows the body to rejuvenate.