A necessary function that is essential for biological rejuvenation and organ recovery.
Sleep is an important factor in multiple health outcomes, including the risk of cardiovascular disease, cancer, and cognition issues, as well as in overallmortality.
A universal function of living species, comprising 1/3 of human life.
Earlier bedtimes and earlier wake times with frequent awakening characterize the sleeping patterns of older adults.
One third of lives spent on sleeping.
Average American sleeps 8.5 hours a day.
Associated with decreased arousal generated by nuclei in the hypothalamus, brainstem, and basal forebrain.
The glymphatic system is turned on during sleep, compromising alertness.
Sleep enhances memory consolidation.
The basic biological need for sleep is unclear.
Brain energy metabolism only declines by 25% during sleep suggesting that sleep does not simply serve to conserve energy
Glymphatic activity is dramatically enhanced during sleep while its function is suppressed during wakefulness.
The sleep state is conducive to convective fluid fluxes and thereby to clearance of metabolites.
A major function of sleep is thought to be that the glymphatic system is turned on and that the brain clears itself of neurotoxic waste products produced during wakefulness.
Normal sleep physiology involves an overall increase in parasympathetic tone and decreased sympathetic tone.
Sinus bradycardia, marked sinus arrhythmia, and sinus pauses of up to 2.6 seconds occur during normal sleep.
2 distinct types exist: nonrapid eye movement (NREM) and rapid eye movement (REM) sleep.
Sleep cycles between REM sleep and non-REM sleep at approximately 90 minute intervals.
Normal sleep begins with a period of nonrapid eye movement sleep during which physiologic functions are gradually diminished in 4 stages.
Following the slowing physiologic stages there is a return from stage 4 to 3 and 2 leading to the first REM sleep.
REM sleep which is the active phase of sleep is manifested by REMs, dreams and EEG activity.
REM normally occupies about 20-25% of sleep time.
REM sleep associated with dreaming, alterations in respiratory and heart rates, penile and clitoral erection and hypotonia of airway and skeletal muscles (Kryger M et al).
REM sleep is characterized by active mentation, i.e. dreams, and skeletal muscle paralysis
REM sleep skeletal muscle atonia is required to prevent dream enactment and promote a period of quiescence.
REM sleep is characterized by a period of unconsciousness that is notable for the eyes darting back and forth, as well as more fluttering of heart rate and changes in respiration.
Vivid dreams are reported during REM sleep, which is marked by Beta waves.
REM sleep is an important time for consolidation of memories, storing knowledge into long-term memories, as well as slow and consolidation from the previous stage.
There are usually 5 – 7 REM periods during a normal night’s sleep.
During periods of pain and depression there’s usually a disruption of normal sleep and REM patterns that negatively affect homeostasis or normal bodily functions.
The NREM-REM cycle is repeated 4-5 times per night with a cycle lasting approximately 90 minutes.
Non REM sleep has 3 EEG stages, with higher amplitude rhythms and lower frequency rhythms with waxing and waning muscle tone, lower temperature and slower heart rate.
Non-R sleep-stage 1 is the earliest and lightest stage of sleep consisting of theta waves when we begin to sleep. One can easily be awakened by any significant stimulus.
Stage 2 occurs when heart rate and respiration begin to even out, body temperatures decrease, and brain waves alternate between short bursts with spindles and longer more complex waves.
Stages 3 and 4 reflect deep sleep, marked by delta waves and or most important in terms of restoring energy, strengthening the immune system, and regulating the release of growth hormones.
As the night progresses REM sleep is increased in duration.
The suprachiasmatic nucleus in the hypothalamus is responsible for the release of melatonin on a 25 hour cycle.
The pineal gland secretes less melatonin when exposed to light.
Neurotransmitters play a role in sleep and include serotonin, norepinephrine and dopamine, when imbalanced these chemical may disrupt sleep.
Excessive sleepiness is the primary symptom seen in work shift disorder, narcolepsy and obstructive sleep apnea.
Adults need 7-9 hours of sleep per night, and shorter or longer durations have been associated with increased morbidity and mortality.
People who get five or fewer hours of sleep a night have 50 percent more calcium in their coronary arteries, an early marker of heart disease.
A longer duration of sleep greater than 10 hours per day is significantly associated with increased overall mortality, including coronary heart disease and cancer related mortality.
Sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality, though the cause is probably other factors such as depression and socioeconomic status.
Sleep duration of less than 10 hours versus less than eight hours is associated with a 32% higher all-cause mortality, 40% higher coronary heart disease, and a 45% higher cancer related mortality.
National Health and Nutrition Examination Survey (NHANES) 2005-2008 37.1% of US adults report sleeping < 7 hours.
A sleep history is evaluated as part of a routine health maintenance examination, as part of the evaluation of symptoms of snoring, apnea, and daytime sleepiness, and during comprehensive evaluation for high-risk individuals with a history of congestive heart failure, obesity, hypertension diabetes and stroke.
Older adults who sleep am average of six hours or less or nine hours or more per night have worse cognitive function and other health outcomes that those who get a normal 7 to 8 hours nightly.
Individuals who report shorter sleep have higher brain amyloid-beta burden and poor performance on memory tests.
Patients who sleep longer hours have similar amyloid-beta burden as those with normal sleep duration but worse executive function test performance.
Both long and short sleepers have higher BMI, greater depression, and more daytime napping than normal sleepers.
People who live the longest report sleeping for six to seven hours each night.
Lack of sleep (<5 hours) more than doubles the risk of death from cardiovascular disease, but too much sleep (>9 hours) is associated with a doubling of the risk of death, though not primarily from cardiovascular disease.
Sleep monitoring of hunter-gatherer tribes from Africa and from South America has shown similar sleep patterns across continents (average sleeping duration is 6.4 hours)>
There is a summer/winter difference of 1 hour.
Afternoon naps are uncommon, and insomnia is very rare, tenfold less than in industrial societies, in hunter gatherer tribes.