The glossopharyngeal nerve (cranial nerve IX) and vagus nerve (cranial nerve X) are often combined, because they exit from the brain stem side-by-side, and have similar and frequently overlapping functional and anatomical distributions in the periphery. These nerves both connect with many of the same brain stem nuclei, and are often damaged together.
In general, the glossopharyngeal nerve contains more sensory fibers, including from the posterior 1/3 of the tongue and pharynx, down to the level of the larynx, which is where the vagus nerve takes over. The vagus nerve is motor to the palate elevators and constrictors of the pharynx, which occurs in swallowing and gagging.
Cranial Nerve IX: Glossopharyngeal
This nerve has motor, sensory, and autonomic nervous system nerve fibers.
It, along with the vagus nerve, provides some innervation to the upper pharyngeal constrictor muscles. It also innervates the stylophayngeus muscles, which elevates the larynx and pulls it forward during the pharyngeal stage of the swallow. This action also aids in relaxation and and opening of the cricopharyngeus muscle.
This nerve mediates all sensation, including taste, from the posterior third of the tongue. It also carries sensation from the velum and superior portion of the pharynx.
Importance in Speech-Language Pathology
The full importance of the glossopharyngeal nerve on speech is difficult to tease out, because damage to it will also affect the vagus nerve. However, it does play a role in speech resonance and phonation by shaping the pharynx into the appropriate positions needed to produce various phonemes correctly.
To test to see if the glossopharyngeal nerve is functioning correctly, a clinician would have his/her patient stick out their tongue while they use a tongue depressor or cotton tip to press against one side of the posterior pharyngeal wall. With a gentle poking of the wall, a gag should be elicited.
Both sides of the pharynx should be tested, and if a gag is not present after stimulation, the examiner should ask the patient if they feel pressure of touch. If the stimulus is felt and no gag occurs, only the motor portion of the gag (mediated by the vagus) may be impaired, but this is rare. The absence of this sensation implicates the glossophayngeal nerve and gives the clinician information that is important in a swallowing assessment.
Cranial Nerve X: Vagus
The vagus nerve is one of the main nerves for swallowing and can cause major problems, if injured. There are three main branches of the vagus: the pharyngeal, external superior laryngeal, and recurrent nerve branch.
This nerve is responsible for raising the velum as it innervates the glossopalatine and levator veli palatine muscles. As stated before, it works with the glossophayngeal nerve to innervate the pharyngeal constrictor muscles and intrinsic musculature of the larynx. The vagus is also responsible for vocal fold adduction (closing) during the swallow. It controls the muscles involved in swallowing, as well as those that control respiration.
The vagus carries sensory information from the velum and posterior and inferior portions of the pharynx. It also mediates sensation in the larynx.
While evaluation of swallowing function involves both the glossopharyngeal and vagus, palatal function is controlled primarily by the vagus. First, the clinician should observe the palate at rest as the patient opens the mouth to allow viewing. The clinician would check to see that the palatal arches are symmetrical, and that both arches hang equally. Next, the clinician would ask the patient to phonate, “ah” and observe. During observation while phonating, the soft palate should elevate and move posteriorly and symmetrically. Damage to this nerve may cause paralysis or paresis of the vocal folds. The clinician may also ask the patient to say “ka, ka, ka” to check for any nasal emission.
Importance in Speech-Language Pathology
This nerve is one of the most important cranial nerves for speech production. Each of the three branches of the vagus nerve have special importance for motor speech production.
The pharyngeal branch provides motor innervation for many muscles of the pharynx. Bilateral damage to this branch can have significant effect on resonance, because almost all the muscles of the velum will have weakness or paralysis. Speech will be moderately or severely hypernasal, and pressure consonants (fricatives, affricates and stops) may be weak and distorted because of nasal emission of air through the open velopharyngeal port.
The external superior laryngeal nerve branch innervates the cricothyroid muscle of the larynx, which helps to stretch and tense the vocal folds during speech to control vocal pitch. Bilateral damage may result in an individual’s decreased loudness and increased breathiness, having notable difficulty changing vocal pitch.
The recurrent nerve branch supplies motor innervation for all the adductor and abductor muscles of the vocal folds. Unilateral damage will cause breathy phonation and decreased vocal fold loudness, because the damaged vocal fold is halfway between being fully adducted or fully abducted. Bilateral damage will cause the vocal folds to be fixed in a position, which may be close enough to permit phonation, but it may be very breathy and hoarse.
Testing of CN IX and X by Kyndall Allred (clinician) and Erin Stewart (client):