CN IX comprises sensory, motor, somatosensory and para-sympathetic fibres. The sensory fibres conduct stimuli from the taste buds of the posterior part of the tongue. The motor fibres innervate the stylopharyngeal muscle, the somatosensory fibres innervate the posterior part of the tongue, the pharyngeal wall and the tonsils and the parasympathetic fibres innervate the parotid gland.
CN X contains motor, somatosensory and parasympathetic fibres. The motor fibres innervate the random muscles in the roof of the mouth, the larynx and the pharynx. The parasympathetic fibres innervate muscles of the oesophagus, bronchi, heart, lungs, ileum and part of the colon. The somatosensory fibres are responsible for sensitivity of the outer ear canal, amongst other things.
CN IX and CN X are generally examined together.
Procedure
- Ask the patient to open their mouth and assess the position of the palatal arches [Figure 31a].
- Ask the patient to say ‘ah’ or ‘ee’.
- Note whether the palatal arches contract upwards symmetrically.
- Try to gently touch the posterior pharyngeal wall using a spatula.
- Note whether this evokes a gag reflex.
- Compare left and right.
- If the patient has a hoarse voice, you can use indirect laryngoscopy to gain an impression of how the vocal cords are functioning.
Figure 31a
Interpretation
If the uvula and palatal arches pull to one side upon phonation, it suggests loss of function of the CN X motor fibres on the opposite side [Figure 31b]. If the pharyngeal wall pulls to one side in response to the gag reflex, it is indicative of a lesion in the CN X motor fibres on the opposite side. If the patient does not feel you touching the pharyngeal wall, it indicates loss of function of the CN IX somatosensory fibres. During the acute phase of a unilateral lesion in the recurrent nerve, there will be aphonia. The vocal cords are then in the paramedial position. Later, the ‘healthy’ vocal cord will lie against the paralysed vocal cord during phonation, resulting in a hoarse voice.
During the acute phase of a bilateral lesion in the recurrent nerve, aphonia will also be seen. Due to the dominant quality of the adductor muscles, both vocal cords can also be in the medial position. The patient will then display inspiratory stridor as well as a hoarse voice.
Similar to trigeminal neuralgia, glossopharyngeal neuralgia can also occur, although less commonly. Here too, the diagnosis should be based on the history-taking. No abnormalities will be found upon examination.
Figure 31b