Sleep is Naturally Recurring State of Mind and Body

Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity, and inhibition of nearly all voluntary muscles during Rapid Eye Movement (REM) sleep, and reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli, but is more reactive than a coma or disorders of consciousness, with sleep displaying different, active brain patterns, which occur in repeating periods: REM sleep and Non-REM sleep. Humans may suffer from various sleep disorders, including dyssomnias such as insomnia, hypersomnia, narcolepsy, and sleep apnea; parasomnias such as sleepwalking and Rapid Eye Movement sleep behavior disorder; bruxism; and circadian rhythm sleep disorders.

Sleep Meaning

It is a condition of body and mind that typically recurs for several hours every night, in which the nervous system is relatively inactive, the eyes closed, the postural muscles relaxed, and consciousness practically suspended.

Sleep Timing

Sleep timing is controlled by the circadian clock (Process C), sleep-wake homeostasis (Process S), and to some extent by the individual will.

Circadian clock

Sleep timing depends greatly on hormonal signals from the circadian clock, or Process C, a complex neurochemical system that uses signals from an organism’s environment to recreate an internal day-night rhythm. Process C counteracts the homeostatic drive for sleep during the day (in diurnal animals) and augments it at night. The suprachiasmatic nucleus (SCN), a brain area directly above the optic chiasm, is presently considered the most important nexus for this process.

Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts), long-distance travel, and the influence of universal indoor lighting. Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely, they can have difficulty waking up in the trough of the cycle. 

Process S

Generally speaking, the longer an organism is awake, the more it feels a need to sleep. This driver is referred to as Process S. The balance between sleeping and waking is regulated by a process called homeostasis. Induced or perceived lack of sleep is called sleep deprivation.

Process S is driven by the depletion of glycogen and accumulation of adenosine in the forebrain that disinhibits the ventrolateral preoptic nucleus, allowing for inhibition of the ascending reticular activating system.

Social timing

Humans are also influenced by aspects of social time, such as the hours when other people are awake, the hours when work is required, the time on clocks, etc. Time zones, standard times used to unify the timing for people in the same area, correspond only approximately to the natural rising and setting of the sun.

An extreme example of the approximate nature of time zones is China, a country that used to span five time zones and now officially uses only one (UTC+8).

Distribution

In polyphasic sleep, an organism sleeps several times in a 24-hour cycle, whereas in monophasic sleep this occurs all at once. Under experimental conditions, humans tend to alternate more frequently between sleep and wakefulness if they have nothing better to do.

Given a 14-hour period of darkness in experimental conditions, humans tended towards bimodal sleep, with two sleep periods concentrated at the beginning and at the end of the dark time. Bimodal sleep in humans was more common before the industrial revolution. Seven-year-olds are better disposed to wake up early in the morning than are fifteen-year-olds. Chronotypes far outside the normal range are called circadian rhythm sleep disorders.

Naps

Naps are short periods of sleep that one might take during the daytime, often in order to get the necessary amount of rest. Napping is often associated with childhood, but around one-third of American adults partake in it daily. The optimal nap duration is around 10-20 minutes.

As researchers have proven that it takes at least 30 minutes to enter slow-wave sleep, the deepest period of sleep. Napping too long and entering the slow wave cycles can make it difficult to awake from the nap and leave one feeling unrested. This period of drowsiness is called sleep inertia.

Genetics

Monozygotic (identical) but not dizygotic (fraternal) twins tend to have similar sleep habits. Neurotransmitters, molecules whose production can be traced to specific genes, are one genetic influence on sleep that can be analyzed. The circadian clock has its own set of genes.

Sleep Quality

The quality of sleep may be evaluated from an objective and a subjective point of view. Objective sleep quality refers to how difficult it is for a person to fall asleep and remain in a sleeping state, and how many times they wake up during a single night. Poor sleep quality disrupts the cycle of transition between the different stages of sleep. Subjective sleep quality in turn refers to a sense of being rested and regenerated after waking. 

Homeostatic sleep propensity must be balanced against the circadian element for satisfactory sleep. Along with corresponding messages from the circadian clock, this tells the body it needs to sleep.

Ideal duration of Sleep

Human sleep needs vary by age and amongst individuals; sleep is considered to be adequate when there is no daytime sleepiness or dysfunction. Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy. Those affected with sleep state misperception may typically report having slept only four hours despite having slept a full eight hours.

Researchers have found that sleeping 6–7 hours each night correlates with longevity and cardiac health in humans, though many underlying factors may be involved in the causality behind this relationship.

Sleep difficulties

Sleep difficulties are furthermore associated with psychiatric disorders such as:

• Depression,
• Alcoholism, and
• Bipolar disorder.

Up to 90 percent of adults with depression are found to have sleep difficulties. Sleep duration can also vary according to season. Up to 90% of people report longer sleep duration in winter, which may lead to more pronounced seasonal affective disorder.

Sleep in Children

By the time infants reach the age of two, their brain size has reached 90 percent of an adult-sized brain; a majority of this brain growth has occurred during the period of life with the highest rate of sleep. The hours that children spend asleep influence their ability to perform cognitive tasks. Children who sleep through the night and have few night-waking episodes have higher cognitive attainments and easier temperaments than other children.

Sleep also influences language development. To test this, researchers taught infants a faux language and observed their recollection of the rules for that language. Infants who slept within four hours of learning the language could remember the language rules better, while infants who stayed awake longer did not recall those rules as well. There is also a relationship between infants’ vocabulary and sleeping: infants who sleep longer at night at 12 months have better vocabularies at 26 months.

Hours of sleep

Children need many hours of sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as the child ages. Early in 2015, after a two-year study, the National Sleep Foundation in the US announced newly revised recommendations as shown in the table below:

Hours of Sleep are Recommended for Each Age Group

Age and condition	Sleep needs
Newborns (0–3 months)	14 to 17 hours
Infants (4–11 months)	12 to 15 hours
Toddlers (1–2 years)	11 to 14 hours
Preschoolers (3–4 years)	10 to 13 hours
School-age children (5–12 years)	9 to 11 hours
Teenagers (13–17 years)	8 to 10 hours
Adults (18–64 years)	7 to 9 hours
Older Adults (65 years and over)	7 to 8 hours

Sleep Functions

Restoration

The human organism physically restores itself during sleep, occurring mostly during slow-wave sleep during which body temperature, heart rate, and brain oxygen consumption decrease. In both the brain and body, the reduced rate of metabolism enables countervailing restorative processes.

The brain requires sleep for restoration, whereas these processes can take place during quiescent waking in the rest of the body.

The essential function of sleep may be its restorative effect on the brain: “Sleep is of the brain, by the brain, and for the brain.” This theory is strengthened by the fact that sleep is observed to be a necessary behavior across most of the animal kingdom, including some of the least evolved animals that have no need for other functions of sleep, such as memory consolidation or dreaming.

Memory processing

It has been widely accepted that sleep must support the formation of long-term memory, and generally increase previous learning and experience recalls. However, its benefit seems to depend on the phase of sleep and the type of memory.

Dreaming

During sleep, especially REM, humans tend to experience dreams. These are elusive and mostly unpredictable first-person experiences that seem logical and realistic to the dreamer while they are in progress, despite their frequently bizarre, irrational, and/or surreal qualities that become apparent when assessed after waking. Dreams often seamlessly incorporate concepts, situations, people, and objects within a person’s mind that would not normally go together. They can include apparent sensations of all types, especially vision and movement.

Dreams tend to rapidly fade from memory after waking. Some people choose to keep a dream journal, which they believe helps them build dream recall and facilitate the ability to experience lucid dreams.

Counterintuitively, penile erections during sleep are not more frequent during sexual dreams than during other dreams. The parasympathetic nervous system experiences increased activity during REM sleep which may cause the erection of the penis or clitoris. In males, 80% to 95% of REM sleep is normally accompanied by partial to full penile erection, while only about 12% of men’s dreams contain sexual content.

Sleep Disorders

Insomnia

It is a general term for difficulty falling asleep and/or staying asleep. Insomnia can have many different causes, including psychological stress, a poor sleep environment, an inconsistent sleep schedule, or excessive mental or physical stimulation in the hours before bedtime.

The sleep environment may be improved by installing heavy drapes to shut out all sunlight, and keeping computers, televisions, and work materials out of the sleeping area.

Obstructive sleep apnea

Obstructive sleep apnea is a condition in which major pauses in breathing occur during sleep, disrupting the normal progression of sleep and often causing other more severe health problems. Apneas occur when the muscles around the patient’s airway relax during sleep, causing the airway to collapse and block the intake of oxygen. Obstructive sleep apnea is more common than central sleep apnea. As oxygen levels in the blood drop, the patient then comes out of deep sleep in order to resume breathing.

Diagnosing sleep apnea usually requires a professional sleep study performed in a sleep clinic, because the episodes of wakefulness caused by the disorder are extremely brief and patients usually do not remember experiencing them. Major risk factors for sleep apnea include chronic fatigue, old age, obesity, and snoring.

Aging and sleep

People over age 60 with prolonged sleep (8–10 hours or more; average sleep duration of 7–8 hours in the elderly) have a 33% increased risk of all-cause mortality and 43% increased risk of cardiovascular diseases, while those with short sleep (less than 7 hours) have a 6% increased risk of all-cause mortality.

SLEEP DISORDERS, including SLEEP APNEA, INSOMNIA, or periodic limb movements, occur more commonly in the elderly, each possibly impacting sleep quality and duration.

Other disorders

Sleep disorders include:

• Narcolepsy,
• Periodic limb movement disorder (PLMD),
• Restless leg syndrome (RLS),
• Upper airway resistance syndrome (UARS), and
• Circadian rhythm sleep disorders.

Fatal familial insomnia, or FFI, an extremely rare genetic disease with no known treatment or cure, is characterized by increasing insomnia as one of its symptoms; ultimately sufferers of the disease stop sleeping entirely, before dying of the disease. Somnambulism, known as sleepwalking, is a sleeping disorder, especially among children.

Sleep health

Low quality sleep

Low quality sleep has been linked with health conditions like cardiovascular disease, obesity, and mental illness. While poor sleep is common among those with cardiovascular disease, some research indicates that poor sleep can be a contributing cause.

Sleep duration greater than nine hours is also correlated with coronary heart disease, as well as stroke, and cardiovascular events.

Children and adults

In both children and adults, short sleep duration is associated with an increased risk of obesity, with various studies reporting an increased risk of 45–55%.

Other aspects of sleep health have been associated with obesity, including daytime napping, sleep timing, the variability of sleep timing, and low sleep efficiency. However, sleep duration is the most studied for its impact on obesity.

Symptoms of mental illness

Sleep problems have been frequently viewed as a symptom of mental illness rather than a causative factor. However, a growing body of evidence suggests that they are both a cause and a symptom of mental illness. Insomnia is a significant predictor of major depressive disorder.

Some studies have also indicated a correlation between insomnia and anxiety, post-traumatic stress disorder, and suicide. Sleep disorders can increase the risk of psychosis and worsen the severity of psychotic episodes.

Good sleep hygiene habits

Having good sleep hygiene can help to improve your physical and mental health by providing your body with the necessary rejuvenation only restful sleep can provide. 

Some ways to improve sleep health include:

• Going to sleep at consistent times every night,
• Avoiding any electronic devices such as televisions in the bedroom,
• Getting adequate exercise throughout your day, and
• Avoiding caffeine in the hours before going to sleep.

Another way to greatly improve sleep hygiene is by creating a peaceful and relaxing sleep environment. Sleeping in a dark and clean room with things like a white noise maker can help facilitate restful sleep.

Drugs and diet that induce Sleep

Drugs that induce sleep

• Benzodiazepines although these interfere with REM;
• Nonbenzodiazepine hypnotics such as eszopiclone (Lunesta), zaleplon (Sonata), and zolpidem (Ambien);
• Antihistamines, such as diphenhydramine (Benadryl) and doxylamine;
• Alcohol (ethanol), despite its rebound effect later in the night and interference with REM;
• Barbiturates have the same problem;
• Melatonin, a component of the circadian clock, and released naturally at night by the pineal gland; and
• Cannabis may also interfere with REM.

Stimulants, which inhibit sleep

• Caffeine, an adenosine antagonist;
• Amphetamine, MDMA, empathogen-entactogens, and related drugs;
• Cocaine, which can alter the circadian rhythm, and methylphenidate, which acts similarly; and
• Other analeptic drugs like modafinil and armodafinil with poorly understood mechanisms.

Consuming high amounts of the stimulant caffeine can result in interrupted sleep patterns and sometimes sleep deprivation. This vicious cycle can result in drowsiness which can then result in higher consumption of caffeine in order to stay awake the next day. This cycle can lead to decreased cognitive function and an overall feeling of fatigue.

Dietary and nutritional choices

Dietary and nutritional choices may affect sleep duration and quality. One 2016 review indicated that a high-carbohydrate diet promoted a shorter onset of sleep and a longer duration of sleep than a high-fat diet.

A 2012 investigation indicated that mixed micronutrients and macronutrients are needed to promote quality sleep. A varied diet containing fresh fruits and vegetables, low saturated fat, and whole grains may be optimal for individuals seeking to improve sleep quality. High-quality clinical trials on long-term dietary practices are needed to better define the influence of diet on sleep quality.

Sleep in Mythology

Sleep has been seen in culture as similar to death since antiquity; in Greek mythology, Hypnos (the god of sleep) and Thanatos (the god of death) were both said to be the children of Nyx (the goddess of night). John Donne, Samuel Taylor Coleridge, Percy Bysshe Shelley, John Keats, and other poets have all written poems about the relationship between sleep and death. Shelley describes them as “both so passing, strange and wonderful!” Keats similarly poses the question: “Can death be sleep, when life is but a dream”. 

The earliest of these stories is the ancient Greek legend of Epimenides of Knossos. According to the biographer Diogenes Laërtius, Epimenides was a shepherd on the Greek island of Crete. One day, one of his sheep went missing and he went out to look for it, but became tired and fell asleep in a cave under Mount Ida. When he awoke, he continued searching for the sheep, but could not find it, so he returned to his old farm, only to discover that it was now under new ownership. He went to his hometown but discovered that nobody there knew him. Finally, he met his younger brother, who was now an old man, and learned that he had been asleep in the cave for fifty-seven years.

Siddha remedies for healthy Sleep

Reference: https://en.wikipedia.org/wiki/Sleep