Overview
The facial nerve, or cranial nerve (CN) VII, is the nerve of facial expression. The pathways of the facial nerve are variable, and knowledge of the key intratemporal and extratemporal landmarks is essential for accurate physical diagnosis and safe and effective surgical intervention in the head and neck. (See the image below.)
The surgical anatomy and landmarks of the facial nerve.
The facial nerve is composed of approximately 10,000 neurons, 7,000 of which are myelinated and innervate the nerves of facial expression. Three thousand of the nerve fibers are somatosensory and secretomotor and make up the nervus intermedius. The course of the facial nerve and its central connections can be roughly divided into the segments listed in Table 1, below.
Table 1. Segmental Description of the Facial Nerve and Central Connections (Open Table in a new window)
|
Segment |
Location |
Length, mm |
|
Supranuclear |
Cerebral cortex |
NA |
|
Brainstem |
Motor nucleus of facial nerve, superior salivatory nucleus of tractus solitarius |
NA |
|
Meatal segment |
Brainstem to internal acoustic meatus or canal (IAC) |
13-15 |
|
Labyrinthine segment |
Fundus of IAC to facial hiatus |
3-4 |
|
Tympanic segment |
Geniculate ganglion to pyramidal eminence |
8-11 |
|
Mastoid segment |
Pyramidal eminence to stylomastoid foramen |
10-14 |
|
Extratemporal segment |
Stylomastoid foramen to pes anserinus |
15-20 |
The objective of this article is to briefly review the anatomy of the facial nerve in each of these segments and to follow the nerve from its most proximal origin to its end organ; ie, the muscles of facial expression. [NA = Not applicable]