Stapedius is supplied by
**Core Concept**
The stapedius muscle is a small, skeletal muscle in the middle ear that plays a crucial role in sound modulation and protection. It is innervated by a cranial nerve branch that arises from the facial nerve, demonstrating a complex relationship between the motor and sensory functions of the facial nerve.
**Why the Correct Answer is Right**
The correct answer is the facial nerve, specifically its tympanic branch, which supplies the stapedius muscle. This branch arises from the facial nerve's mastoid segment and enters the middle ear through the pyramid of the temporal bone. The stapedius muscle contracts in response to loud sounds, stabilizing the stapes bone and preventing damage to the inner ear.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the vagus nerve primarily supplies the parasympathetic innervation to various organs, including the heart, lungs, and gastrointestinal tract, and is not associated with the stapedius muscle.
**Option B:** This option is incorrect because the glossopharyngeal nerve primarily supplies the stylopharyngeus muscle and provides sensory innervation to the posterior one-third of the tongue, the tonsils, and the pharynx.
**Option C:** This option is incorrect because the trigeminal nerve primarily supplies the muscles of mastication, including the temporalis, masseter, and medial pterygoid muscles.
**Clinical Pearl / High-Yield Fact**
The stapedius muscle's contraction is a reflex response to loud sounds, known as the stapedius reflex, which helps protect the inner ear from damage.
**Correct Answer: C. The glossopharyngeal nerve supplies the stylopharyngeus muscle and the tympanic branch of the facial nerve supplies the stapedius muscle.