In turn, these nuclei send fibers to the nucleus ambiguus, a motor nucleus in the rostral medulla. These sensations are carried by CN IX, which acts as the afferent limb of the reflex to the ipsilateral nucleus solitarius (also referred to as the gustatory nucleus) after synapsing at the superior ganglion located in the jugular foramen. The stimulus is provided by sensation to the posterior pharyngeal wall, the tonsillar pillars, or the base of the tongue. The nerve roots of cranial nerves IX and X exit the medulla through the jugular foramen and descend on either side of the pharynx to innervate the posterior pharynx, posterior one-third of the tongue, soft palate, and the stylopharyngeus muscle. The gag reflex is controlled by both the glossopharyngeal (CN IX) and vagus (CN X) nerves, which serve as the afferent (sensory) and the efferent (motor) limbs for the reflex arc, respectively. In cases of psychogenic gag reflexes, even the thought of touching a sensitive trigger area, such as occurs when going to the dentist, can induce gagging. A psychogenic gag reflex presents following a mental trigger, typically without direct physical contact. A somatogenic gag reflex follows direct physical contact with a trigger area, which may include the base of the tongue, posterior pharyngeal wall, or tonsillar area. The gag reflex can be classified as either somatogenic or psychogenic.
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