Overview
Moving our
faces is essential to emotional expression, body language and speech. The lack
of function of this nerve is debilitating, and leads to a number of visible and
difficult symptoms. The facial nerve is the seventh cranial nerve and supplies
the muscles of facial expression, taste to the anterior two thirds of the
tongue and the salivary glands.
Gross Anatomy
The facial
nerve is also known as cranial nerve 7. The motor section of the facial nerve
arises from the facial nerve nucleus of the pons. The parasympathetic and
sensory nerves arise from the intermediate nerve. These two parts join together
and cross the posterior cranial fossa. The nerve arises from the pontomedullary
junction, lateral to the abducens and close to the Vestibulocochlear nerve. It
leaves the skull through the internal acoustic meatus along with the
Vestibulocochlear nerve (an opening in the petrous portion of the temporal
bone). The nerve now has an intracranial course through the facial canal
(labyrinthine, tympanic and mastoid segments). The facial nerve forms a bend
here known as the geniculum of the facial nerve. This ganglion contains the
cell bodies of the sensory nerves. The greater petrosal nerve arises from this
ganglion and passes through the pterygoid canal to synapse with the
pterygopalatine ganglion. It supplies the palatine gland, lacrimal gland, ad
nasal gland. It also supplies parasympathetic innervation to the frontal sinus,
sphenoid sinus, maxillary sinus ethmoid sinus and nasal cavity. The postsynaptic
fibres of the greater petrosal nerve innervate the lacrimal gland.
In the
tympanic section the nerves to stapedius and chorda tympani are given off. The
chorda tympani is a special sensory branch that runs through the middle ear,
hitches a ride with the lingual nerve and provides taste to the anterior two
thirds of the tongue. The chorda tympani also synapse with the submandibular
ganglion, which goes onto supply the submandibular and sublingual glands. The
facial nerve also passes through the parotid gland, but does not supply it. The
Glossopharyngeal nerve innervates the parotid gland via the otic ganglion (the
facial nerve also sends a communicating branch to the otic ganglion) The nerve
to stapedius innervates the stapedius muscle (a small muscle that attaches to
the stapes ossicle in the middle ear). This muscle pulls on the stapes, which
dampens down sound when it is loud.
It divides
into its motor and sensory branch. The motor branch leaves the skull via the
stylomastoid foramen and gives off the posterior auricular nerve (which
supplies the scalp muscles around the ear) and innervates all the muscles of
facial expression, via its 5 facial branches (Temporal, zygomatic, buccal, mandibular,
cervical).
Clinical Anatomy
Lower motor neuron facial nerve
lesion i.e. Bell’s palsy- A Bell’s palsy is a lower motor
neurone lesion of the facial nerve. There are numerous causes including
varicella zoster infection. The symptoms include hemiplegia of the face (motor
branches affected), lack of tears (innervation to the lacrimal gland affected),
lack of saliva (submandibular and sublingual gland affected), hyperacusis
(nerve to stapedius affected), dry eye which may lead to corneal ulceration
(orbicularis oculi, a facial muscle is not innervated).
Upper motor neurone facial nerve
lesion- An upper motor neurone lesion of the face presents
in the same way as a lower motor neurone lesion, however an upper motor neurone
lesion present with forehead sparing. This is because the region of the cortex
(from the primary motor strip) innervates the forehead bilaterally, hence the
opposing motor strip compensates for the affected side.
Quick Anatomy
Key Facts
Developmental precursor- Metencephalon (secondary brain vesicle)
Muscles-
Facial muscles, stapedius muscle.
Glands-
Submandibular gland, sublingual gland, lacrimal gland.
Sensation-
Taste of the anterior 2/3 of the tongue.
Aide-Memoire
Acronym for the 5 major facial motor
branches of the facial nerve:
To Zanzibar By Motor Car
Temporal, Zygomatic, Buccal, Mandibular,
Cervical
Summary
The facial
nerve is the seventh cranial nerve and supplies the muscles of facial
expression, taste to the anterior two thirds of the tongue and the salivary
glands.
References
1.
Frank H.Netter
MD: Atlas
of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head and
Neck
2.
Chummy S.Sinnatamby: Last’s
Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier
3.
Richard L.
Drake, A. Wayne Vogl,
Adam. W.M.
Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier
4.
Elliiot L.Manchell: Gray's Clinical Neuroanatomy:
The
Anatomic Basis for Clinical Neuroscience