SN1
SHORT NOTE
5M
★ High-yield
Describe the course and branches of the facial nerve. Differentiate upper from lower motor neurone facial palsy.
Origin and Course
The facial nerve (VII) is the nerve of the second pharyngeal arch, a mixed nerve with motor, secretomotor and gustatory fibres.
Branches and Functions
| Branch | Function | Effect of injury above it |
|---|---|---|
| Greater petrosal | Secretomotor to the lacrimal gland (via the pterygopalatine ganglion) and to nasal and palatine glands | Loss of lacrimation — dry eye |
| Nerve to stapedius | Dampens the stapes | Hyperacusis — painful sensitivity to sound |
| Chorda tympani | Taste from the anterior two-thirds of the tongue; secretomotor to the submandibular and sublingual glands | Loss of taste and of salivation |
| Posterior auricular, digastric, stylohyoid | Occipitalis, posterior belly of digastric, stylohyoid | — |
| Five terminal branches | All the muscles of facial expression, buccinator, platysma | Facial paralysis |
- Terminal branches — temporal, zygomatic, buccal, marginal mandibular, cervical; mnemonic "Ten Zebras Bit My Cat"
- The level of the lesion is deduced from which of these functions are lost — the practical value of knowing the order of the branches
Upper and Lower Motor Neurone Lesions
| Feature | Upper motor neurone | Lower motor neurone |
|---|---|---|
| Forehead (frontalis) | Spared — the upper face has bilateral cortical supply | Paralysed |
| Eye closure | Preserved | Lost — Bell phenomenon |
| Lower face | Paralysed (contralateral) | Paralysed (same side) |
| Emotional movement | May be preserved | Lost |
| Example | Stroke | Bell palsy |
Applied Aspects
- Bell palsy — idiopathic lower motor neurone facial palsy, probably viral; sudden onset, often with pain behind the ear. Most recover; steroids given early improve the outcome
- The eye must be protected — loss of blinking and of the corneal reflex risks exposure keratitis; artificial tears and taping at night
- Ramsay Hunt syndrome — herpes zoster of the geniculate ganglion; facial palsy with vesicles in the external auditory meatus and severe pain
- Parotid surgery and malignancy — the nerve traverses the gland, so a facial palsy with a parotid lump suggests carcinoma
- Forceps delivery may compress the nerve at the stylomastoid foramen, which is superficial in the newborn as the mastoid process is undeveloped
All questions in Head & Neck
- Q1Describe the triangles of the neck with their boundaries and contents. Add a note on the posterior triangle and its applied anatomy. ★
- Q2Describe the thyroid gland under relations, blood supply and nerve relations. Add a note on the applied anatomy of thyroidectomy. ★
- Q3Describe the parotid gland under bed, structures within it, duct and nerve supply. Add a note on its applied anatomy. ★
- Q4Describe the larynx under cartilages, cavity, muscles and nerve supply. Add a note on vocal cord palsy. ★
- Q5Describe the cavernous sinus with its contents and connections. Add a note on cavernous sinus thrombosis and the dangerous area of the face. ★
- SN1Describe the course and branches of the facial nerve. Differentiate upper from lower motor neurone facial palsy. ★
- SN2Describe the temporomandibular joint with its movements. Add a note on its dislocation. ★
- SN3Describe the submandibular gland with its relations, duct and nerve supply. ★
- SN4Describe the layers of the deep cervical fascia and the fascial spaces of the neck. ★
- SN5Describe the tongue with its papillae, muscles and nerve supply. Add a note on hypoglossal nerve palsy. ★
- SN6Describe the layers of the scalp with their clinical importance. ★
- SN7Describe the trigeminal nerve with its divisions and distribution. Add a note on the associated parasympathetic ganglia.