The hypoglossal nerve is the motor nerve to all of the muscles of the tongue except, the:
**Core Concept**
The hypoglossal nerve (CN XII) is a motor nerve that primarily supplies the extrinsic and intrinsic muscles of the tongue, playing a crucial role in tongue movements such as protrusion, retraction, and elevation. The tongue muscles are essential for speech, swallowing, and mastication.
**Why the Correct Answer is Right**
The hypoglossal nerve innervates all the intrinsic muscles of the tongue (superior, middle, and inferior longitudinal, transverse, and vertical muscles) and the extrinsic muscles (genioglossus, hyoglossus, and styloglossus). However, the lingual nerve, a branch of the mandibular division of the trigeminal nerve (CN V3), is responsible for the innervation of the palatoglossus muscle, which elevates the tongue and helps form the palate. This muscle is part of the palatine muscles and is involved in swallowing and speech.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the question asks for the exception, and the hypoglossal nerve does indeed innervate the extrinsic muscles.
**Option B:** Incorrect because the hypoglossal nerve supplies the intrinsic muscles of the tongue, not the lingual nerve.
**Option C:** Incorrect because the styloglossus muscle is one of the extrinsic muscles innervated by the hypoglossal nerve.
**Clinical Pearl / High-Yield Fact**
The hypoglossal nerve is often tested in clinical exams due to its association with the lingual nerve, which is involved in the sensation of the anterior two-thirds of the tongue. A mnemonic to remember the extrinsic muscles of the tongue is: "GHS", which stands for Genioglossus, Hyoglossus, and Styloglossus.
**Correct Answer:** D. Palatoglossus