Welcome back to Anatomy dissected by complete. Anatomy.
Here's another cranial nerve for you.
This time, it's cranial nerve 7: the facial nerve
As usual we'll have a look at the function and course of this nerve and apply that knowledge as we consider facial paralysis
The facial nerve is primarily known for supplying the muscles of facial expression
It also has a supplementary role in receiving taste sensation from part of the tongue, and in the distribution of autonomic
innervation to the salivary and lacrimal glands
Okay, let's get stuck into the anatomy.
The facial nerve emerges from the lower margin of the pons where it meets the medulla oblongata below
It emerges as two distinct routes
The motor route, often called the facial motor route (or the facial nerve proper) and the intermediate nerve
The motor root contains motor neurons
The intermediate nerve carries sensory and parasympathetic fibers
These two nerves remain distinct as they enter the internal acoustic meatus in the petrous part of the temporal bone
The intermediate nerve and the motor route merge just within the temporal bone
Here the bone has been faded so we can see what's going on inside
The two merged nerves are referred to as the facial nerve
Just inside the temporal bone is the geniculate ganglion
This small swelling
It's located on the first of three 90-degree turns of the facial nerve
The greater petrosal nerve branches from the ganglion inside the bone and travels anteriorly to the pterygopalatine ganglion
To supply the lacrimal, nasal, palatine, and pharyngeal glance with parasympathetic innervation
The complex course of the facial nerve within the facial canal can be appreciated in this posterior view
Inside the bone, just after the second 90-degree turn, a small branch passes anteriorly into the middle ear
Which we can appreciate in this lateral view
This is chorda tympani
It is so named because it runs behind the tympanic membrane
It exits on the anterior side of the temporal bone to join the lingual nerve
where it picks up special sensory information from the anterior 2/3 of the tongue
Additionally, chorda tympani carries parasympathetic innervation to the submandibular and sublingual glands via the lingual nerve
The rest of the facial nerve carries purely motor innervation
The facial nerve takes one last intracranial turn before it emerges from the stylomastoid foramen
a small hole located between the styloid process and the mastoid process of the temporal bone
It's not visible here, but before it emerges the facial nerve gives a small branch to the stapedius muscle within the middle ear
Following its exit from the cranium, two small motor branches emerge
medially is a branch that will provide innervation to the stylohyoid muscle and
Laterally a nerve innervating the posterior belly of digastric muscle
There is a larger motor branch that bifurcates from the terminal branch and passes posteriorly. This is the posterior auricular nerve
It supplies the occipital belly of occipitofrontalis
and arecularis muscles
The terminal part of the facial nerve enters the posterior edge of the parotid gland and travels between the deep and superficial
divisions of this gland
As it traverses the glans, it divides into five branches
Here's a mnemonic to help you remember the names of these branches:
They are
the temporal nerve
the zygomatic nerve
the buccal nerve
mandibular nerve
and cervical nerve
Each of these branches supply a subset of the muscles of facial expression around the eye, cheeks, mouth and into the neck
The most common cause of facial nerve palsy is Bell's palsy
which is idiopathic
meaning the cause is unknown. It results in unilateral dysfunction of the facial nerve most obviously exhibited in paralysis of the facial muscles
Diagnosis of the condition is based on appearance and excluding other causes of paralysis
Recovery is usually spontaneous within three weeks.
And that's it! Another cranial nerve to tick off the list
Hopefully now you have a better understanding of the facial nerve
including its course through the temporal bone and parotid gland
As well as its autonomic and somatic functions in the face tongue and glands
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