Brainwaves Sleep System

Category: File - :Hermaphrodite endormi face.jpg|thumb|300px|Sleeping Hermaphroditus

Category: File - :Anker Schlafender Knabe im Heu.jpg|thumb|300px|Boy sleeping in a hay pile

Sleep is a naturally recurring state of relatively suspended sensory and motor activity, characterized by total or partial unconsciousness and the inactivity of nearly all voluntary muscles.Macmillan Dictionary for Students Macmillan, Pan Ltd. (1981), page 936. Retrieved 2009-10-1. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and it is more easily reversible than hibernation or coma. It is observed in all mammals, all birds, and many reptiles, amphibians, and fish. In humans, other mammals, and a substantial majority of other animals that have been studied (such as some species of fish, birds, ants, and fruit flies), regular sleep is essential for survival.

The purposes and mechanisms of sleep are only partially clear and are the subject of intense research.

Electroencephalography (EEG) is the recording of electrical activity along the scalp produced by the firing of neurons within the brain.E. Niedermeyer, Lopes da Silva, F., Electroencephalography, 4th Ed., 1999, Williams & Wilkins, Baltimore, MD, 1258 pp. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20?40 minutes, as recorded from multiple electrodes placed on the scalp. In neurology, the main diagnostic application of EEG is in the case of epilepsy, as epileptic activity can create clear abnormalities on a standard EEG study.Atlas of EEG & Seizure Semiology. B. Abou-Khalil; Musilus, K.E.; Elsevier, 2006. A secondary clinical use of EEG is in the diagnosis of coma, encephalopathies, and brain death. EEG used to be a first-line method for the diagnosis of tumors, stroke and other focal brain disorders, but this use has decreased with the advent of anatomical imaging techniques such as MRI and CT.

Derivatives of the EEG technique include evoked potentials (EP), which involves averaging the EEG activity time-locked to the presentation of a stimulus of some sort (visual, somatosensory, or auditory). Event-related potentials refer to averaged EEG responses that are time-locked to more complex processing of stimuli; this technique is used in cognitive science, cognitive psychology, and psychophysiological research.

Category: Image - :Spike-waves.png|thumb|450px|Epileptic spike and wave discharges monitored with EEG.

A sleep disorder (somnipathy) is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental and emotional functioning. A test commonly ordered for some sleep disorders is the polysomnogram.

Sleep deprivation, a sleep disorder characterized by having too little sleep, can be either chronic or acute. Long-term sleep deprivation causes certain death in severe cases, especially with lab animals. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight gains.

Complete absence of sleep over long periods is impossible to achieve; brief microsleeps cannot be avoided.

Sleep apnea (or sleep apnoea in British English) is a sleep disorder characterized by pauses in breathing during sleep. Each episode, called an apnea ( (ápnoia), from ?- (a-), privative, ?????? (pnéein), to breathe), lasts long enough so that one or more breaths are missed, and such episodes occur repeatedly throughout sleep. "Sleep Apnea 101 The standard definition of any apneic event includes a minimum 10 second interval between breaths, with either a neurological arousal (a 3-second or greater shift in EEG frequency, measured at C3, C4, O1, or O2), a blood oxygen desaturation of 3-4% or greater, or both arousal and desaturation. Sleep apnea is diagnosed with an overnight sleep test called a polysomnogram, or a "sleep study".

Clinically significant levels of sleep apnea are defined as five or more episodes per hour of any type of apnea (from the polysomnogram). There are three distinct forms of sleep apnea: central, obstructive, and complex (i.e., a combination of central and obstructive) constituting 0.4%, 84% and 15% of cases respectively.Mayo Clinic Discovers New Type Of Sleep Apnea Breathing is interrupted by the lack of respiratory effort in central sleep apnea; in obstructive sleep apnea, breathing is interrupted by a physical block to airflow despite respiratory effort. In complex (or "mixed") sleep apnea, there is a transition from central to obstructive features during the events themselves.

Regardless of type, the individual with sleep apnea is rarely aware of having difficulty breathing, even upon awakening. Sleep apnea is recognized as a problem by others witnessing the individual during episodes or is suspected because of its effects on the body (sequelae). Symptoms may be present for years (or even decades) without identification, during which time the sufferer may become conditioned to the daytime sleepiness and fatigue associated with significant levels of sleep disturbance.