Absence of the gag reflex and pharyngeal sensation can be a symptom of a number of severe medical conditions, such as damage to the glossopharyngeal nerve, the vagus nerve, or brain death.
In unilateral (one-sided) glossopharyngeal nerve (CNIX- sensory component) damage, there will be no gag response when touching the pharyngeal wall on the same side of the damaged nerve. With one-sided vagal nerve (CNX- motor component) damage, the soft palate will elevate and pull toward the intact side regardless of the side of the pharynx that is touched. This is because the sensory component is intact on both sides, but only the motor nerves supplying one side of the soft palatine and pharyngeal muscles is working, therefore the contraction of the muscles in the reflex is asymmetrical. If both CN IX and X are damaged on one side (not uncommon), stimulation of the normal side elicits only a unilateral response, with deviation of the soft palate to that side; no consensual response is seen. Touching the damaged side produces no response at all.
At one point, it was thought that a lack of the gag reflex in stroke patients was a good predictor for dysphagia (difficulty with swallowing) or laryngeal aspiration (food or drink entering the larynx), and was therefore commonly checked for. However, in one study, 37% of healthy people did not have a gag reflex, yet all subjects except for one still retained an intact pharyngeal sensation. These results suggest that the muscles that control the gag reflex remain independent of those that control normal swallowing. Since this reflex is commonly not found in healthy people, its predictive value in determining the risk for swallowing disorders is severely limited. Pharyngeal sensation, on the other hand, as seen by this study, is rarely absent, and could prove better at predicting future problems with swallowing.
Read more about this topic: Gag Reflex
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