Testing of this nerve is based on the fact that (a) the nerve carries fibres of taste from the posterior one third of the tongue; and (b) that it provides sensory innervation to the pharynx.
1. Sensations of taste can be tested by applying substances that are salty (salt), sweet (sugar), sour (lemon), or bitter (quinine) to the posterior one third of the tongue. The mouth should be rinsed and the tongue dried before the substance is applied.
2. Touching the pharyngeal mucosa causes reflex constriction of pharyngeal muscles. The glossopharyngeal nerve provides the afferent part of the pathway for this reflex.
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