Facial Nerve (CN VII)
The facial nerve is the seventh cranial nerve with diverse functions including facial expression, taste from the anterior tongue, lacrimation, and salivation. It has the most complex intracranial course of any cranial nerve, passing through the temporal bone via the facial canal.
Origin
Motor: facial motor nucleus in pons; Sensory/Parasympathetic: nervus intermedius from superior salivatory nucleus and solitary nucleus
Foramina
Internal acoustic meatus (entry), Stylomastoid foramen (exit)
Course
Exits pontomedullary junction → enters internal acoustic meatus → traverses facial canal (geniculate ganglion) → exits via stylomastoid foramen → parotid gland → facial branches
Functions
- •Facial expression muscles
- •Taste from anterior 2/3 of tongue
- •Lacrimation (tear production)
- •Salivation (submandibular, sublingual glands)
- •Stapedius muscle (dampens loud sounds)
- •Efferent limb of corneal reflex
Branches
Structures Innervated
- →Muscles of facial expression
- →Stapedius
- →Posterior belly of digastric
- →Stylohyoid
- →Taste: anterior 2/3 tongue
- →Parasympathetic: lacrimal, submandibular, sublingual glands
Clinical Testing
Test facial symmetry at rest and with expression (raise eyebrows, close eyes tight, smile, puff cheeks). Check taste on anterior tongue. Assess corneal reflex (V1 afferent, VII efferent).
Clinical Relevance
Bell's palsy is idiopathic facial paralysis affecting the entire hemiface (forehead included). Upper motor neuron lesions (stroke) spare the forehead due to bilateral cortical innervation of upper face. Ramsay Hunt syndrome is facial palsy with herpes zoster.
Study Tips
- ✓"To Zanzibar By Motor Car" = Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical
- ✓Bell's palsy = entire face; Stroke = lower face only (forehead spared)
- ✓Hyperacusis indicates lesion proximal to stapedius branch
- ✓Loss of taste + dry mouth = lesion proximal to chorda tympani
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Common questions about this cranial nerve
The forehead muscles receive bilateral upper motor neuron input (both hemispheres). A unilateral stroke leaves the contralateral input intact. Bell's palsy affects the lower motor neuron, paralyzing all ipsilateral facial muscles including the forehead.
Both cause facial paralysis, but Ramsay Hunt syndrome is caused by herpes zoster reactivation in the geniculate ganglion. It presents with vesicles in the ear canal and is associated with more severe paralysis and poorer recovery.
The facial nerve innervates the stapedius muscle, which dampens ossicle vibration. When paralyzed (proximal lesion), sounds seem abnormally loud (hyperacusis). This helps localize the lesion to the facial canal proximal to the stapedius branch.