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A yawn is a reflex consisting of the simultaneous inhalation of air and the stretching of the eardrums, followed by an exhalation of breath. Yawning (''oscitation'') most often occurs in adults immediately before and after sleep, during tedious activities and as a result of its contagious quality. It is commonly associated with tiredness, stress, sleepiness, or even boredom and hunger, though studies show it may be linked to the cooling of the brain.〔Popular Mechanics, January 2012 edition〕 In humans, yawning is often triggered by others yawning (e.g., seeing a person yawning, talking to someone on the phone who is yawning) and is a typical example of positive feedback.〔Camazine, Deneubourg, Franks, Sneyd, Theraulaz, Bonabeau, ''Self-Organization in Biological Systems'', Princeton University Press, 2003. ISBN 0-691-11624-5, ISBN 0-691-01211-3 (pbk.) p. 18.〕 This "contagious" yawning has also been observed in chimpanzees, dogs, and can occur across species. Approximately 20 physiological reasons for yawning have been proposed by scholars, but there is little agreement about its main functions.〔 ==Etymology== English ''yawn'' continues a number of Middle English forms, ''yanen'' from Old English ''ġānian'', and ''yenen, yonen'' from Old English frequentatives ''ġinian, ġionian'', from a Germanic root '' *gīn-''. The Germanic root has Indo-European cognates, from a root '' *g̑hēi-''〔Pokorny (1959:419-422): "g̑hē- : ghə-, and g̑hēi- 'to gape, yawn'", Pokorny (1959:449): "g̑hēu- : g̑hō(u)- : g̑həu- 'to gape, yawn'"〕 found also with ''-n-'' suffix in Greek χαίνω "to yawn", and without the ''-n-'' in English ''gap'' (compare the ''figura etymologica'' in Norse ''ginnunga-gap'') ''gum'' "palate" and ''gasp'' (via Old Norse), Latin ''hiō, hiatus'', and Greek ''chasm, chaos''. The Latin term used in medicine is ''oscitatio'' (anglicized as ''oscitation''), from the verb ''oscito'' "to open the mouth". ''Pandiculation'' is the act of yawning and stretching simultaneously.〔(MedOnline.net ), "pandiculate"〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「yawn」の詳細全文を読む スポンサード リンク
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