Hyperacusis in Bell’s palsy is due to the paralysis of the following muscle:
**Core Concept**
Bell's palsy is a condition characterized by sudden onset of unilateral facial paralysis due to idiopathic inflammation of the facial nerve. Hyperacusis, or increased sensitivity to sound, is a common symptom in patients with Bell's palsy. The underlying mechanism involves the paralysis of the stapedius muscle, which normally regulates sound by contracting in response to loud noises.
**Why the Correct Answer is Right**
The stapedius muscle is a small muscle located in the middle ear, innervated by the facial nerve (cranial nerve VII). It contracts in response to loud noises, stabilizing the stapes bone and reducing the transmission of sound to the inner ear. When the stapedius muscle is paralyzed due to facial nerve damage, it fails to contract normally, leading to an increased sensitivity to sound, known as hyperacusis.
**Why Each Wrong Option is Incorrect**
* **Option A:** The digastric muscle is a muscle of facial expression that is innervated by the mandibular division of the trigeminal nerve (cranial nerve V3) and is not involved in regulating sound.
* **Option B:** The tensor tympani muscle is a muscle of the middle ear, innervated by the trigeminal nerve (cranial nerve V), but it does not play a significant role in regulating sound in response to loud noises.
* **Option C:** The tensor veli palatini muscle is a muscle of the palate, innervated by the mandibular division of the trigeminal nerve (cranial nerve V3), and is not involved in regulating sound.
**Clinical Pearl / High-Yield Fact**
In patients with Bell's palsy, the paralysis of the stapedius muscle can be temporarily alleviated with the use of earplugs or earmuffs, which can help to reduce the sensitivity to sound.
**Correct Answer: C. The stapedius muscle.**