The hypoglossal nerve (CN XII) is the cranial nerve involved in tongue deviation.
Understanding Tongue Deviation and the Hypoglossal Nerve
Damage to the hypoglossal nerve results in paralysis of the tongue. This paralysis typically affects one side of the tongue. When an individual with hypoglossal nerve damage protrudes their tongue, it will deviate, pointing toward the damaged side.
How to Assess the Hypoglossal Nerve
The hypoglossal nerve's function is often assessed by observing the tongue's position and appearance while it is at rest and during movement.
- Observation at Rest: The tongue is examined for any signs of atrophy (muscle wasting) or fasciculations (involuntary muscle twitching).
- Observation During Protrusion: The patient is asked to stick out their tongue. Deviation to one side indicates weakness on that side, suggesting hypoglossal nerve damage on the side to which the tongue deviates.
Example Scenario: Hypoglossal Nerve Damage
Imagine a patient who has suffered a stroke affecting the left side of their brain. During a neurological examination, when they are asked to stick out their tongue, it deviates to the left. This indicates damage to the left hypoglossal nerve or its associated pathways. The tongue deviates toward the weaker side because the stronger (unaffected) side pushes it in that direction.
Summary Table: Hypoglossal Nerve and Tongue Deviation
| Cranial Nerve | Function | Effect of Damage |
|---|---|---|
| Hypoglossal (XII) | Controls tongue movement (motor function) | Tongue paralysis, deviation towards the side of the lesion when protruded. Atrophy and fasciculations may also be present. |
