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The pharyngeal reflex or gag reflex (also known as a laryngeal spasm) is a reflex contraction of the back of the throat, evoked by touching the roof of the mouth, the back of the tongue, the area around the tonsils and the back of the throat. It, along with other aero digestive reflexes such as reflexive pharyngeal swallowing, prevents something from entering the throat except as part of normal swallowing and helps prevent choking. ==Reflex arc== In a reflex arc, a series of physiological steps occur very rapidly to produce a reflex. Generally a sensory receptor receives an environmental stimulus, in this case from objects reaching nerves in the back of the throat, and sends a message via an afferent nerve to the central nervous system (CNS). The CNS receives this message and sends an appropriate response via an efferent nerve (also known as a motor neuron) to effector cells located in the same initial area that can then carry out the appropriate response. In the case of the pharyngeal reflex: *the sensory limb is mediated predominantly by CN IX (glossopharyngeal nerve) *the motor limb by CN X (vagus nerve). The gag reflex involves a brisk and brief elevation of the soft palate and bilateral contraction of pharyngeal muscles evoked by touching the posterior pharyngeal wall. Touching the soft palate can lead to a similar reflex response. However, in that case, the sensory limb of the reflex is the CN V (trigeminal nerve). In very sensitive individuals, much more of the brain stem may be involved; a simple gag may enlarge to retching and vomiting in some. 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「Pharyngeal reflex」の詳細全文を読む スポンサード リンク
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