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You are watching: The restorative theory views sleep as ________.

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

Sleep is one extremely complicated process that consists of more than simply closing one’s eyelids and also counting sheep.  it is an active state that unconsciousness developed by the body whereby the mind is in a loved one state that rest and is reactive generally to internal stimulus. The precise purpose of sleep has actually not been fully elucidated.  Several significant theories have explored the brain and effort to identify a objective for why us sleep, which consists of the Inactivity theory, energy conservation theory, restoration theory, and the brain plasticity theory.

Inactivity concept is based upon the concept of evolutionary push where creatures inactive in ~ night were much less likely to dice from the predation that injury in the dark, thus creating an evolutionary and reproductive advantage to gift inactive in ~ night. 

Energy conservation concept posits the the main function of sleep is to mitigate a person"s energy demand during part of the day and night as soon as it is least efficient to hunt because that food. This theory is supported by the fact that the body has decreased metabolism by up to 10% during sleep.

The restorative theory says that sleep permits for the body to repair and replete cellular materials necessary for biological functions that end up being depleted throughout an wake up day. This is backed by the findings numerous functions in the human body such together muscle repair, organization growth, protein synthesis, and release of many of the vital hormones for expansion occur primarily during sleep.

Brain plasticity theory is the sleep is crucial for neural reorganization and growth of the brain’s structure and also function. That is clear that sleep dram a role in the development of the brain in infants and also children and explains why infants must sleep upwards the 14 hours per day.

These theories space not exhaustive or all-inclusive that the widespread ideas; rather, they serve to frame the principle that we carry out not fully understand sleep yet. That is an ext accepted that no solitary theory explains it all, and a combination of these ideas is much more likely to organize the an essential to sleep.<1><2><3><4>


Function

Sleep features in a fairly predictable cyclical pattern between 2 significant phases: Non-rapid eye motion (NREM) sleep and rapid eye motion (REM) sleep. NREM sleep is subdivided into several stages numbered 1 to 3. Each phase and also stage to represent the family member depth the sleep and also offers unique characteristics in the mind wave, muscle tones, and eye activity patterns. As the name implies, NREM is characterized by an lack of eye movements, and also rapid eye motions characterize REM.

Sleep starts with a short NREM stage 1 phase, adhered to by NREM phase 2, then NREM phase 3, then ultimately into REM. NREM account for approximately 75% to 80% of total sleep, and also REM accounts because that the remaining 20% to 25% of sleep. This progression through the stages of sleep occurs in this stimulate of occasions on repeat throughout the night for differing lengths the time. The early stage cycle lasts 70 come 100 minutes to complete fully. However, the staying cycles last 90 come 120 minute each. The lot of REM in every cycle progresses transparent the night from being minimal top top the initiation of sleep but eventually is as much as 30% of the cycle later on in the night. A full of 4 come 5 cycles v this progression is usual in a night.

NREM phase 1 is the shallow phase of sleep whereby a human is still quickly awoken. That lasts 1 to 7 minutes. Rhythmical alpha waves characterize electroencephalogram (EEG) in ~ a frequency of 8 to 13 cycles per second.

NREM stage 2 lasts roughly 10 to 25 minutes in the initial bicycle of sleep yet progresses to consume 50% of the total sleep cycle later on in the night. Stage 2 is a much deeper sleep state than stage 1, yet individuals space still awoken with heavy stimulation. Brainwave task on EEG is low voltage “sleep spindles and K-complexes.” current theories indicate that memory consolidation occurs primarily during this stage.

NREM stage 3 lasts around 20 to 40 minutes, initially. EEG is identified by high-voltage, slow-wave frequency.

REM is the phase of sleep responsible because that dreaming. The is defined by complete body voluntarily muscle paralysis (except for the extraocular muscles). This paralysis is assumed to be a device to protect against neural stimulus from dreams to manifest in yes, really muscular impulses throughout sleep. EEG in REM is “Sawtooth waveforms,” theta waves, and also slow, alpha tide in a desynchronized sample set.<5><6>


Mechanism

The device through i m sorry sleep is generated and maintained is more of a balance in between two systems located within the brain: the homeostatic processes, which space functionally the body’s “need for sleep” center, and the circadian rhythm which is an inner clock for the sleep-wake cycle. 

Sleep Generation is initiated in ~ the ventrolateral preoptic nucleus (VLPO) the the anterior hypothalamus and acts to inhibit the arousal areas of the brain, including the tuberomammillary nucleus, lateral hypothalamus, locus coeruleus, dorsal raphe, laterodorsal tegmental nucleus, and pedunculopontine tegmental nucleus. Hypocretin (orexin) neurons in the lateral hypothalamus aid to facilitate this process in a synergistic effect.

NREM sleep is a sensible disconnection in between the brain stem and also the thalamus and cortex preserved with hyperpolarizing GABA neurons in the reticular activating center of the thalamus and also the cortex. Corticothalamic neurons signal the thalamus, which reasons hyperpolarization of the thalamic reticular neurons.  This process produces delta tide from both thalamic reticular and cortical pyramidal sources. Thus correlating v the varying stages 1 come 3 that NREM.

REM sleep is created by "REM-on neurons" in the mesencephalic and also pontine cholinergic neurons. The pedunculopontine tegmental nucleus and the lateral dorsal tegmental neurons trigger desynchronized cortical waveforms. The tonic component of REM sleep is parasympathetically medicated, and also the phasic ingredient is sympathetically mediated.

Circadian rate is the body’s cyclical nature for the desire for sleep. The hypothalamus controls the via the suprachiasmatic nucleus through sensory input from the retinohypothalamic tract based upon light level detected from the retina. The circadian rate is around 24.2 hours per cycle. Melatonin, created in the pineal gland, has likewise been presented to be a modulator of the circadian rate that has concentrations varied based upon the light level. Melatonin level are greatest at night and decrease throughout the daytime. Finally, human body temperature has been associated as component of the circadian rhythm. The exact collection point varies amongst different people, yet it is meant to have actually generally lower temperature in the morning and higher temperatures in the evening.<5><7>


Related Testing

The primary testing modality supplied to research sleep is polysomnography. This is a multifaceted test that has an electrocardiogram (ECG), electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), and oxygen saturation. Polysomnography should not it is in routinely provided as a screening test. The results of all experimentation modalities room coordinated to paint a full photo of the sleeping status that a patient.

ECG trial and error is the measure up of electrical present through the myocardium of the breath and is offered to diagnose cardiac aberrations, consisting of rate and rhythm.

EEG consists of non-invasively place electrodes throughout the scalp to measure up voltage fluctuations and also current of electrical activity within the brain. The exact variety of electrodes used varies.  The waveforms that the brain are recorded and used to translate the stage of sleep a human being is in and detect any neurological abnormalities during sleep.

EOG is offered to measure up extraocular muscle duty during sleep.  throughout NREM, there should be no eye movement. Thus eye activity is indicative the REM.

EMG is supplied to measure muscle duty of respiration and also peripheral limbs and can detect extreme movement or enhanced tension throughout sleep.

Oxygen saturation is used to verify that respiration is gift performed together expected during sleep without any halts in breathing.<6><8>


Clinical Significance

Insomnia

This is the generic term for any kind of illness the causes an obstacle falling asleep and also staying asleep. This is the most common of sleep illnesses and also is commonly related to emotional stressors, bad sleeping environments, rarely often rare sleep schedules, or too much mental, physical, or chemical stimulation.

Obstructive Sleep Apnea

This is condition where major pauses in breathing occur during sleep second to one obstructive process, such as the collapse of the airway an additional to excessive weight or weak pharyngeal musculature. When the airway collapses, breath stops, and hypoxia drives the body to awaken the end of deep sleep to breath again. As soon as this occurs frequently in the night, restful sleep is no possible. There room 3 degrees of disease with obstructive sleep apnea Mild, Moderate, and Severe. Mild OSA is as soon as there room 5 come 14 illustration of apnea in one hour. Moderate is when there space 15 come 30 apnea illustration in one hour. Serious OSA is as soon as there space 30 or more episodes the OSA in one hour. Optimistic airway pressure therapy characterizes the therapy of OSA: constant Positive Airway push (CPAP) and also Bilevel confident Airway push (BiPAP). CPAP is consistent pressure supplementation that reasons the airway come splint open, permitting for airflow. BiPAP is once the confident pressure supplementation is altered between 2 pressures enabling for the splinting advantage of optimistic pressure and permitting for better ventilation that the lung 보다 CPAP. Additionally used as therapy room mandibular advance devices and also surgical treatment such together uvulopalatopharyngoplasty, adenotonsillectomy, and maxillomandibular advancement. Mainstream therapy is optimistic airway supplementation, no surgical.<9>

Central Sleep Apnea

This illness is comparable to obstructive sleep apnea. However, that is etiology is regarded intrinsic diminution and also ultimately fail of the breathing journey or mechanisms during sleep.  such illnesses encompass congenital main hypoventilation syndrome (Ondine’s curse) or congestive heart failure.  when breathing go not occur effectively, the body will certainly awaken native deep sleep to exactly hypoxia. Treatment consists of CPAP therapy, BiPAP therapy, Adaptive-servo-ventilation, or medical therapy through acetazolamide or theophylline.<10>

Mixed Sleep Apnea (Complex Sleep Apnea)

It is a combination of both obstructive sleep apnea and central sleep apnea symptoms. This is disease where patients v symptoms the obstructive sleep apnea build symptoms of central sleep apnea top top treatment with CPAP therapy during a sleep study. Treatment is commonly very low-pressure CPAP therapy.<11>

Ghrelin-Leptin Abnormalities

Sleep duration has been found to beat a far-ranging role in maintaining body weight. The theory below is the an imbalance in the two important hormones related to hunger (Leptin and Ghrelin) is aberrant with changed sleep habits. Leptin is make by adipose cells and also functions come regulate energy balance by inhibiting the hunger drive. Ghrelin is the counter-regulatory hormone to leptin produced by cholinergic cell in the cradle tract and is responsible for boosting appetite, thus encouraging the hunger drive. Shorter nights of sleep are linked with diminished leptin and also elevated ghrelin. These differences in leptin and ghrelin most likely lead to raised appetite, maybe explaining the raised BMI observed through sleepless nights.   This aberration is commonly connected with OSA because of the truth that increased BMI is straight related come the advancement of OSA. The treatment below is to sleep repeatedly 7 to 8 hrs per night.<12>

Narcolepsy

Narcolepsy kind 1 occurs when nearly all of the neurons that contain orexin (also referred to as hypocretin) are lost. The device of narcolepsy kind 2 is less clear, but it is believed that it might be because of a similar but less significant loss the orexin neurons. During normal REM sleep, orexin decreases, i beg your pardon decreases RAS activity and disclosure atonia. In narcolepsy form 1, the system that separates wake from sleep becomes rough without adequate levels of orexin. The RAS no longer consistently reasons the release of wake-promoting neurotransmitters come the cortex and also inconsistently inhibits the VLPO. This results in rapid transitions between sleep and also wake and enables the intrusion that REM-related phenomena into wakefulness. This is defined by episodes of daytime somnolence, cataplexy, and also occasionally hallucinations throughout the work that extreme emotions may trigger.  Many human being with narcolepsy additionally suffer native insomnia.

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Somnambulism

A state of combined sleep and wakefulness that leads to sleep-walking. Sleepwalking is when a person ambulates or performs actions without consciously controlling the motion or having a memory of the event.  This condition is not completely understood, however it has been linked with increased slow-wave sleep and also sleep deprivation, and also there is proof that over there is a hereditary component of inheritance. Mainstay therapy is composed of benzodiazepines.<6><14>