Cranial Nerves IX (Glossopharyngeal) & X (Vagus) – Functions and Clinical Testing

A set of question-and-answer flashcards reviewing the functions, clinical screening, and examination findings associated with Cranial Nerves IX and X.

Which muscle receives motor fibres from the glossopharyngeal nerve and what does it do?

The stylopharyngeus muscle; it elevates the pharynx during swallowing and speech.

Which cranial nerve conveys taste sensation from the posterior one-third of the tongue?

The glossopharyngeal nerve (Cranial Nerve IX).

Which nerve provides the afferent limb of the gag reflex?

The glossopharyngeal nerve (Cranial Nerve IX).

Which nerve supplies the efferent limb of the gag reflex?

The vagus nerve (Cranial Nerve X).

During mouth inspection, what finding suggests a vagus nerve lesion?

Asymmetrical soft-palate elevation with the uvula deviating away from the side of the lesion.

How does a vagus nerve lesion affect a patient’s cough?

It produces a weak, non-explosive 'bovine' cough due to inability to close the glottis.

What two problems should you ask about when screening for glossopharyngeal and vagus nerve dysfunction?

Difficulty swallowing and any change in voice or cough.

What does coughing or a change in voice immediately after swallowing water suggest?

An ineffective swallow, potentially caused by glossopharyngeal (afferent) or vagus (efferent) nerve pathology.

Why is the swallow assessment often preferred over direct gag-reflex testing?

Because eliciting the gag reflex is highly unpleasant for patients.

Which areas are touched to stimulate the gag reflex during examination?

The posterior aspect of the tongue and the oropharynx.

Absence of a gag reflex can indicate pathology in which cranial nerves?

Either the glossopharyngeal nerve (afferent) or the vagus nerve (efferent).