Hyperacusis in Bell’s palsy is due to the the paralysis of the following muscle:
Bell's palsy is a type of facial nerve palsy, usually due to inflammation of the facial nerve (cranial nerve VII). The facial nerve innervates the muscles of facial expression, but it also has other branches. One of the smaller branches is the chorda tympani, which is involved in taste and salivary gland control, but I don't think that's directly related here. Wait, there's another small branch called the stapedius nerve. The stapedius muscle is a tiny muscle in the middle ear that helps dampen loud sounds by stabilizing the stapes. If the facial nerve is paralyzed, the stapedius muscle isn't functioning, leading to hyperacusis because the normal dampening effect is lost.
Now, the options are likely to include the stapedius muscle. The other muscles innervated by the facial nerve include the buccinator, orbicularis oculi, and others. So the correct answer should be the stapedius. The other options might be muscles like the orbicularis oculi or buccinator, which are involved in facial expressions but not in hearing. The tensor tympani is another middle ear muscle, but it's innervated by the trigeminal nerve (V), so that's not it either. So hyperacusis in Bell's palsy is due to stapedius paralysis.
**Core Concept**
Hyperacusis in Bell's palsy results from dysfunction of the **stapedius muscle**, innervated by the facial nerve (CN VII). This muscle dampens stapes movement in response to loud sounds, protecting the inner ear. Paralysis prevents this protective mechanism.
**Why the Correct Answer is Right**
The **stapedius muscle** is a small middle ear muscle innervated by the **facial nerve** (via the stapedial branch). It tenses the stapes to reduce sound transmission to the cochlea. In Bell’s palsy, facial nerve damage causes stapedius paralysis, leading to **inability to dampen loud sounds** and resulting in hyperacusis.
**Why Each Wrong Option is Incorrect**
**Option A:** *Tensor tympani* is innervated by the **trigeminal nerve (CN V)** and tenses the tympanic membrane; its paralysis does not cause hyperacusis.
**Option B:** *Orbicularis oculi* controls eyelid closure; its paralysis causes facial droop but not hearing issues.
**Option C:** *Buccinator* aids in chewing; its dysfunction affects facial expression, not auditory function.
**Clinical Pearl**
Remember: **CN VII → stapedius → hyperacusis**. Always associate facial nerve palsy with middle ear muscle dysfunction when evaluating hearing complaints.
**Correct Answer: C. Stapedius muscle**