From the Guidelines
Bell's palsy primarily involves the facial nerve, also known as cranial nerve VII (CN VII). This motor nerve controls the muscles of facial expression, including those responsible for eye closure, smiling, frowning, and raising the eyebrows. The facial nerve (CN VII) is one of the most complex cranial nerves and contains branchial motor (innervation to the muscles of facial expression), visceral motor (parasympathetic innervation to most of the glands of the head), general sensory (surface innervations to a small portion of the external ear and tympanic membrane), and special sensory (taste to the anterior two-thirds of the tongue) functions 1. When affected by Bell's palsy, the facial nerve becomes inflamed, compressed, or damaged, typically on one side of the face, resulting in weakness or paralysis of the facial muscles on the affected side.
The symptoms of Bell's palsy can include facial droop, pain around the jaw or ear, hyperacusis, tinnitus, reduced taste, and decreased lacrimation or salivation. The facial nerve has several branches that innervate different facial muscle groups, including temporal, zygomatic, buccal, mandibular, and cervical branches, all of which can be affected in Bell's palsy. While the facial nerve is the primary motor nerve involved, some patients may experience associated symptoms related to other cranial nerve functions because the facial nerve also carries parasympathetic fibers for tear and saliva production and taste fibers for the anterior two-thirds of the tongue. According to the most recent study, the facial nerve (CN VII) is the primary nerve involved in Bell's palsy 1.
Key points to consider in Bell's palsy include:
- The facial nerve (CN VII) is the primary motor nerve involved
- The nerve has several branches that innervate different facial muscle groups
- Inflammation, compression, or damage to the facial nerve can cause weakness or paralysis of the facial muscles
- Associated symptoms may include facial droop, pain, hyperacusis, tinnitus, reduced taste, and decreased lacrimation or salivation
- The facial nerve also carries parasympathetic fibers for tear and saliva production and taste fibers for the anterior two-thirds of the tongue.
From the Research
Motor Nerves Involved in Bell's Palsy
- The primary motor nerve involved in Bell's palsy is the 7th cranial nerve, also known as the facial nerve 2, 3, 4.
- The facial nerve is responsible for controlling the muscles of facial expression, and its dysfunction leads to the characteristic symptoms of Bell's palsy, including unilateral facial weakness, reduced forehead wrinkling, nasolabial fold flattening, drooping of the corner of the mouth, and drooling 3.
- The facial nerve has both motor and non-motor components, and recognition of its anatomy and function is crucial for the diagnosis and management of Bell's palsy 4.
Key Points
- Bell's palsy is a common outpatient problem, and its diagnosis is usually straightforward, but a number of diagnostic pitfalls can occur 4.
- The treatment of Bell's palsy typically involves corticosteroids, which are probably effective in increasing the likelihood of a complete recovery, and antivirals, which may be possibly effective in combination with corticosteroids 5, 4, 6.
- The outcome of Bell's palsy is generally favorable, even without treatment, but treatment with corticosteroids significantly increases the likelihood of improvement 4, 6.