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.
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).
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.
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.
Acronym for the 5 major facial motor branches of the facial nerve:
To Zanzibar By Motor Car
Temporal, Zygomatic, Buccal, Mandibular, Cervical
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.
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