Hypoglossal Nerve - Testing The Hypoglossal Nerve

Testing The Hypoglossal Nerve

To test the function of the nerve, a person is asked to poke out his/her tongue. If there is a loss of function on one side (unilateral paralysis), the tongue will point toward the affected side, due to unopposed action of the genioglossus muscle (which pulls the tongue forward) on the side of the tongue that is usually innervated. This is the result of a lower motor neuron lesion (the damaged neuron directly innervates the skeletal muscle), and can lead to fasciculations and atrophy of the tongue.

The strength of the tongue can be tested by getting the person to poke the inside of his/her cheek, and feeling how strongly he/she can push a finger pushed against the cheek - a more elegant way of testing than directly touching the tongue.

The tongue can also be looked at for signs of lower motor neuron disease, such as fasciculation and atrophy.

Paralysis/paresis of one side of the tongue results in ipsilateral curvature of the tongue (apex toward the impaired side of the mouth); i.e., the tongue will move toward the affected side.

Cranial Nerve XII is innervated by the contralateral cortex, so a purely upper motor neuron (cortex) lesion will cause the tongue to deviate away from the side of the cortical lesion. Additionally, the fasciculations and atrophy seen in lower motor neuron lesions are not present.

Weakness of the tongue is displayed as a slurring of speech. The tongue may feel "thick", "heavy", or "clumsy." Lingual sounds (i.e., l's, t's, d's, n's, r's, etc.) are slurred and this is obvious in conversation.