During cranial nerve examination, a neurologist asks a 33 year old patient to protrude his tongue. On doing so, her tongue detes to the right side. This finding results from paralysis of tongue muscle namely?
## **Core Concept**
The question tests the understanding of cranial nerve innervation of the tongue, specifically the motor innervation that controls tongue movement. The tongue's motor function is primarily controlled by the **hypoglossal nerve (CN XII)**, with the **genioglossus muscle** being the key muscle for protrusion.
## **Why the Correct Answer is Right**
When the patient protrudes her tongue and it deviates to the right, it indicates weakness of the genioglossus muscle on the right side. The genioglossus muscle is innervated by the **hypoglossal nerve (CN XII)**. When this muscle contracts, it helps to protrude the tongue. If one side is weakened due to paralysis of CN XII, the healthy side will push the tongue towards the weakened side upon protrusion. Therefore, the correct answer involves the muscle primarily responsible for tongue protrusion, which is the **genioglossus**, innervated by CN XII.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a muscle; hence, it cannot be evaluated.
- **Option B:** This option might refer to another muscle or structure but without specifics, it's hard to directly refute. However, the key muscle for protrusion is the genioglossus.
- **Option C:** Similarly, this option lacks specificity but typically, other muscles like the styloglossus or hyoglossus are involved in tongue retraction or depression, not primary protrusion.
- **Option D:** This option is incorrect because, although it might relate to tongue movement, the deviation to one side upon protrusion specifically points towards an issue with the genioglossus muscle.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that a **unilateral lesion of CN XII** results in a tongue that **deviates to the side of the lesion** upon protrusion. This is because the intact genioglossus muscle pushes the tongue towards the weakened side. Remembering this helps in localizing neurological lesions.
## **Correct Answer:** . **Genioglossus**