Stanford Facial Nerve Center

Make an Appointment

(650) 736-3223

What is the Facial Nerve?

The facial nerve is the 7th cranial nerve and carries nerve fibers that control facial movement and expression. The facial nerve also carries nerves that are involved in taste to the anterior 2/3 of the tongue and producing tears (lacrimal gland). It has small branches involved in moderating our sensitivity to noise volume (stapedius muscle) and several other muscles not involved in routine facial expression1.

The cells that transmit information within the facial nerve originate in the base of the brain, or the brain stem, in a region called the pons. The nerve must therefore travel through the base of the skull in order to reach the face. Along this route, the facial nerve travels in close proximity to the eighth cranial nerve, the vestibulocochlear nerve, which is responsible for hearing and balance. The facial nerve exits the base of the skull at the stylomastoid foramen, which is an opening in the bone located near the base of the ear.

[1] Pepper JP. Facial Paralysis and Facial Reanimation. Facial Plastic and Reconstructive Surgery: A Comprehensive Study Guide. 2016 Apr 6:109.
 

Facial nerves and muscle


The facial nerve then enters the parotid gland, and branches into five divisions (see above). The facial nerve has five main branches, although the anatomy can vary somewhat between individuals. The branches are, from top to bottom: frontal (or temporal), zygomatic, buccal, marginal mandibular, and cervical.  Each of these branches provides input to a group of muscles of facial expression.

The following is a rough guide to the areas each branch innervates.  Note that there is some “cross-talk,” or overlap of the circuitry, between branches.

Frontal (temporal):  The muscles of the forehead

Zygomatic:  The muscles involved in forceful eye closure

Buccal:  The muscles involved in moving the nostril, upper lip, spontaneous eye blinking, and raising the corner of the mouth to smile.

Marginal mandibular branch:  The muscles involved in depressing the lower lip

Cervical:  lower chin muscle (platysma), often tensed during facial hair shaving.  It also lowers the corner of the mouth
 

Injury or impairment in a given branch of the nerve can therefore result in:

Frontal:  Paralysis of the forehead/inability to move the eyebrow. Usually, this means the eyebrow ‘hangs down’ in front of the eye and can impair vision

Frontal:  Paralysis of the forehead/inability to move the eyebrow. Usually, this means the eyebrow ‘hangs down’ in front of the eye and can impair vision

Zygomatic:  Difficulty with forceful eye closure. 

Buccal:  Difficulty with smiling and motion of the mouth. This leads to problems with speech, particularly sounds like “bee” and “papa,” where precise motion of the lips is required to articulate the sound. Food or liquid may fall out of the mouth unexpectedly due abnormal lip movement. In addition, there can be difficulty with nasal obstruction on the affected side as the muscles that help keep the nostril open may be paralyzed, resulting in an obstructed nostril. Normal blinking may be slowed or absent. 

Marginal mandibular: the muscles it innervates are involved with downward motion of the corner of the mouth. Injury here may result in an asymmetric smile and problems with eating and drinking.

Cervical:  This is arguably the least important of the branches.  Injury of this nerve results in paralysis of the platysma muscle, a thin sheet that lies just deep to the skin.  This may cause lower lip asymmetry during smile in some patients.
 

What are the causes of facial paralysis? 

Category

Includes

Annual Incidence

Percentage

Idiopathic

Bell’s Palsy

75,396

49.6

Infectious

Lyme disease, Otitis media

23,222

15.3

Neoplastic

Acoustic Neuroma, Parotid malignancy 

20,508

13.5

Neurologic

Stroke, Guillan Barre

20,508

13.5

Traumatic

Temporal bone fracture, birth trauma

12,365

8.1

Total

 

151,999

 

Pepper JP. Facial Paralysis and Facial Reanimation. Facial Plastic and Reconstructive Surgery: A Comprehensive Study Guide. 2016 Apr 6:109.