What is nerve supply of stapedius?
**Core Concept**
The stapedius muscle is a small skeletal muscle in the middle ear responsible for stabilizing the stapes bone and regulating sound transmission. The nerve supply to the stapedius muscle is crucial for its function in sound modulation.
**Why the Correct Answer is Right**
The stapedius muscle is innervated by the facial nerve (cranial nerve VII), specifically through its nerve to the stapedius branch. This branch originates from the facial nerve's mastoid segment and provides motor innervation to the stapedius muscle. The nerve supply to the stapedius muscle allows for the reflexive contraction of the muscle in response to loud sounds, which helps to protect the inner ear from damage.
**Why Each Wrong Option is Incorrect**
**Option A:** The trigeminal nerve (cranial nerve V) is primarily responsible for sensory innervation of the face and motor innervation of muscles involved in mastication, making it an incorrect choice for the nerve supply of the stapedius muscle.
**Option B:** The glossopharyngeal nerve (cranial nerve IX) is involved in swallowing and taste, but not the innervation of the stapedius muscle.
**Option C:** The vagus nerve (cranial nerve X) has various functions, including parasympathetic innervation of the head and neck, but it is not responsible for the nerve supply of the stapedius muscle.
**Clinical Pearl / High-Yield Fact**
The stapedius reflex is an important clinical finding that can be assessed during a hearing evaluation. Abnormalities in the stapedius reflex can indicate issues with the facial nerve or the stapedius muscle itself.
**Correct Answer:** B. Glossopharyngeal nerve