The human body’s functions are coordinated by a complex system of nerves, including twelve pairs of cranial nerves that emerge directly from the brain and control various sensory and motor functions. Among these, the hypoglossal nerve, Cranial Nerve XII (CN XII), plays a specific role in controlling tongue movements. This article explains how the hypoglossal nerve is assessed during a neurological examination.
The Hypoglossal Nerve: Function and Importance
The hypoglossal nerve primarily controls the muscles of the tongue. It enables intricate tongue movements for speech articulation. Dysfunction can lead to slurred speech.
It is also important for swallowing. It coordinates tongue movements to maneuver food and initiate swallowing. Dysfunction can cause difficulty moving the tongue, problems with chewing and swallowing, or changes in speech clarity, prompting assessment.
Performing the Hypoglossal Nerve Test
Assessment involves clinical maneuvers to observe tongue appearance and function. It begins with a visual inspection of the tongue at rest. The examiner looks for muscle wasting (atrophy), appearing as a shrunken or wrinkled tongue, and fasciculations (small, involuntary muscle twitches) indicating nerve damage.
Next, the tongue’s ability to protrude is tested. The individual is asked to stick their tongue straight out. A healthy nerve allows symmetrical protrusion. Deviation to one side indicates weakness on that side.
After protrusion, range of motion and coordination are assessed. The individual moves their tongue side to side, touching each corner of their mouth, and up and down towards their nose and chin. This evaluates tongue mobility and control.
Finally, tongue strength is evaluated. The individual presses their tongue firmly against the inside of one cheek while the examiner applies gentle resistance to the outside. This is repeated on the opposite side. This determines if tongue muscles generate adequate force, assessing motor function.
Understanding Test Results and Next Steps
Normal findings indicate a healthy nerve, with no atrophy or fasciculations at rest. Normal protrusion is straight, with full, symmetrical range of motion side-to-side and up-and-down. Strength testing shows the tongue pressing firmly against resistance.
Abnormal findings, such as atrophy, fasciculations, tongue deviation upon protrusion, limited movement, or weakness against resistance, suggest hypoglossal nerve issues. For instance, deviation to one side upon protrusion indicates weakness on that side. These findings suggest nerve damage or an underlying neurological condition.
These tests are components of a comprehensive neurological examination. An abnormal finding alone does not provide a definitive diagnosis but signals the need for further medical evaluation. The healthcare professional interprets results within the individual’s symptoms and medical history to determine next steps, which may include additional diagnostic imaging or specialist referral.