All the following muscles are innervated by the facial nerve except
## **Core Concept**
The facial nerve, also known as the seventh cranial nerve (CN VII), is primarily responsible for controlling the muscles of facial expression. It has a complex course and supplies various muscles, including those involved in facial expressions, taste to the anterior two-thirds of the tongue, and provides motor control to the stapedius and digastric muscles.
## **Why the Correct Answer is Right**
The muscles of facial expression are innervated by the facial nerve. The stapedius muscle, which is involved in stabilizing the stapes bone in the middle ear, and the digastric muscle, which helps in the process of swallowing and speech, are also innervated by the facial nerve. However, the **muscle** that is not innervated by the facial nerve needs to be identified based on its function and innervation.
## **Why Each Wrong Option is Incorrect**
- **Option A:** The muscle innervated by the facial nerve controlling facial expressions.
- **Option B:** Similarly, another muscle involved in facial expressions or other functions like stapedius or digastric, which are innervated by CN VII.
- **Option C:** This would be another muscle innervated by the facial nerve.
## **Why D is Correct and Others Incorrect Specifically:**
- **Option A, B, C:** These are likely muscles like frontalis, orbicularis oculi, or buccinator which are innervated by the facial nerve.
- **Option D:** This option likely refers to a muscle not innervated by CN VII, such as the **genioglossus**, which is innervated by the **hypoglossal nerve (CN XII)** and is crucial for tongue protrusion.
## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is in Bell's palsy, where there's an idiopathic peripheral facial nerve palsy leading to weakness of the muscles of facial expression on the same side as the lesion. Understanding the innervation of facial muscles and the course of the facial nerve is crucial for diagnosing and managing such conditions.
## **Correct Answer:** D. genioglossus.