Bell’s palsy is paralysis of
**Core Concept**
Bell's palsy is an idiopathic, acute peripheral facial nerve (seventh cranial nerve) palsy, characterized by sudden onset of unilateral facial paralysis or weakness. The facial nerve is responsible for controlling the muscles of facial expression, taste sensation from the anterior two-thirds of the tongue, and parasympathetic innervation to the lacrimal and submandibular glands.
**Why the Correct Answer is Right**
The facial nerve, also known as the seventh cranial nerve (CN VII), is a mixed nerve that carries both motor and sensory fibers. In Bell's palsy, the facial nerve is compressed or inflamed, leading to dysfunction of the motor fibers that control facial expression, resulting in weakness or paralysis of the affected side of the face. This condition is often caused by viral reactivation, such as herpes simplex virus, and can also be associated with other conditions like diabetes mellitus.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Bell's palsy specifically affects the facial nerve (CN VII), not the trigeminal nerve (CN V), which is responsible for sensation in the face and motor control of mastication.
**Option B:** This option is incorrect because Bell's palsy is not a condition of the hypoglossal nerve (CN XII), which is responsible for motor control of the tongue.
**Option C:** This option is incorrect because Bell's palsy is not a condition of the vagus nerve (CN X), which is responsible for various functions including swallowing, vocal cord control, and parasympathetic innervation to various organs.
**Option D:** This option is incorrect because Bell's palsy is not a condition of the glossopharyngeal nerve (CN IX), which is responsible for swallowing, taste sensation from the posterior one-third of the tongue, and parasympathetic innervation to the parotid gland.
**Clinical Pearl / High-Yield Fact**
Bell's palsy is a self-limiting condition, with spontaneous recovery in most cases within 6 weeks. Early treatment with corticosteroids and antiviral medications can improve outcomes and reduce the risk of persistent weakness or synkinesis.
**Correct Answer:** A. Facial nerve (seventh cranial nerve).