hi let's talk about the facial nerve in this video we'll discuss the facial nerve cranial
nerve seven its distribution and its branches distal to the style of mastoid foramen so the
facial nerve first enters the temporal bone through the internal acoustic meatus which we
conceived there sort of on that lateral surface of the petrous portion of the temporal seven is
entering with eight so facial and vestibular cochlea are going in through that opening the
facial nerve then takes a turn and enters into an osseous canal called the facial canal the
facial canal is z shaped and it is the largest osseous canal for a nerve within the canal there
are going to be three branches two of them are going to be parasympathetic branches that will
conduct preganglionic parasympathetic fibers the other will be a motor branch and then the
remainder of the nerve will continue on to exit through the style of mastoid foramen as
the motor trunk so here we can see a lateral view of the skull this is the styloid process of the
temporal I'm sorry this is the mastoid process of the temporal this is the styloid process of
the temporal and nestled between the two right there is the stylomastoid foramen we could also
see the external acoustic meatus there and so coming through that style of mastoid foramen is
going to be the motor trunk for facial within the canal there are going to be three branches that
are going to be important these are going to be outside of the scope of this particular session
but they're going to come strongly into play in subsequent sessions so facial nerve in the
canal the greater patrol the nerve that greater petrosal nerve is going to conduct preganglionic
parasympathetic fibers to the pterygopalatine ganglion so from that pterygopalatine ganglion
postganglionic fibers are going to hitchhike along V 2 to pair sympathetically serve the
lacrimal gland to produce tears for the eye also within that canal is going to originate the chorda
tympani the chorda tympani is going to travel through the middle ear it's going to exit the
skull and be in a place called the infratemporal fossa where it's going to hitchhike along with
branches of a v3 nerve called the lingual nerve and just off at the lingual nerve is
the submandibular ganglion that submandibular ganglion serves the sublingual salivary gland
and the submandibular salivary gland and so those preganglionic parasympathetic fibers of
chorda tympani are serving those salivary glands then we have the nerve to the stapedius muscle
so the stapedius muscle is a middle ear muscle that inserts on the stay piece that helps to
dampen any vibrations of the stapes so as to protect from loud sounds and then the remainder
of the motor root comes out the style of mastoid foramen and it is going to serve the occipital
belly of occipital frontal and the muscles around the ear or the auricular muscles in particular
the posterior auricular muscles sometimes a little bit of the superior auricular muscle
this motor route is also going to serve one half of the digastric muscle so the posterior
belly of digastric gets served as well as the stylohyoid muscle and then the remainder of that
motor route is going out to serve the muscles of facial expression or the mimetic muscles and so
this is how the nerve gets its name because it is serving facial muscles so here's that lateral view
again of the skull there is the external acoustic meatus the styloid process I've got it right this
time the mastoid process and there in between is that stylomastoid foramen so here we see a
lateral view of the of the head with the parotid gland and much of the parotid masseteric fossa
stripped away as also part of the the superficial musculoaponeurotic system stripped away so that
we can see the divisions of the facial nerve so there's the temporal facial division there is
the cervical facial division these divisions are going to innervate the facial muscles so they'll
each have sets of branches and these branches are named regionally by where they're heading
to so our temporofacial temp oral and facial division has temporal branches to serve the
temporozygomatic branches which is going over the zygomatic bone up towards the eye buccal branches
buccal cheek and then there is the cervical facial division cervical facial also has buccal branches
serving the cheek a marginal mandibular branch serving that inferior margin the mandible and then
a cervical branch that's right there that is going down to innervate the platysma now these branches
are are very conceptual and hyper variable and so you shouldn't expect every donor to to have
the the same branching pattern or even to have these large divisions there's there's quite a
bit of variation amongst people but for the most part look to where these branches are heading and
name the branches by what region they're going to so let's take a look at the lateral face again
this time with the parotid gland intact so it is in situ we also have the platysma muscle in
situ and we can see these nerves exiting from the substance of the parotid gland and heading off to
innervate various things which is very cool so one of the one of the nubs that we can see here
is the posterior auricular nerve that posterior auricular nerve is coming around the posterior
oracle to the posterior of the oracle the oracle is this portion of the year and it's going to
innervate the occipital belly of occipitofrontalis as well as the posterior auricular muscle
and sometimes it might even give a branch to the superior auricular muscle but that muscle is
typically served by the temporal branches of facial there's also the nerve to the digastric that nerve
to the digastric is serving the posterior belly of the digastric muscle as well as stylohyoid
muscle then we have all of the facial branches and the facial branches are easily remembered by the
very anatomically geeky mnemonic ten zebras bit my coccyx the coccyx is the tail I guess I should
say because this is a head and neck Anatomy course that's something that you would get in
in a full bodied anatomy course but ten zebras bit my coccyx so ten temporal zebras zygomatic
bit buccal my marginal mandibular coccyx cervical branch so we can see some temporal branches some
zygomatic branches some buccal branches a marginal mandibular branch and then we can see the cervical
branch diving deep to the platysma there and again these these branches are are very conceptual and
highly variable and so you know no two patterns are going to be precisely alike now in identifying
these various branches I think that it's helpful to look for certain landmarks and so superior ly
here one landmark that I look for is the lateral canthus of the eye and I kind of draw a line from
that lateral canthus oops back to stylomastoid foramen and anything superior to that line I call
a temporal branch anything inferior to that line but not down around the cheek region is a
zygomatic branch here we can see a collection of muscles that are going to affect the oral fissure
or the the mouth and so any of the the fibers heading towards these muscles here are going
to be buccal branches so anything in that and the cheek region heading towards the mouth is
a buccal branch along the most inferior margin of the mandible like right along the base there
is the marginal mandibular so they named that well and then the cervical branch cervical neck is the
that actually descends into the neck so that goes inferior to the mandible and that leads us to our
assessment question that being the facial canal of the temporal bone begins at the internal acoustic
meatus and ends at which distal opening the external acoustic meatus mm-hmm no that's that's
your ear hole that's the space through which sound is traveling to the tympanic membrane foramen
magnum well that would be a circuitous route no that's brainstem vertebral arteries etc foramen
rotundum no that's that's v3 petrotympanic fissure no that's actually the space through
which chorda tympani enters the infratemporal fossa and so that leaves the stylomastoid
foramen nestled between the styloid and mastoid processes of the temporal bone is where that
motor route is emerging from the facial canal out into the the face so thank you very much for your time