hi let's talk about the cutaneous innervation of the face in this video we'll discuss the
dermatomes of the face and head the divisions of the trigeminal nerve which served these dermatomes
and branches from each of these divisions so here you're looking at a left lateral view of a head
and the blue dotted lines represent the boundaries between the various dermatomes of the head a
dermatome is a region of skin which is a family served by a single nerve and it's probably best
to also note that there is some overlap between sensory innervation of adjacent dermatomes now
the face is afferently served by the trigeminal nerve tri three geminal meaning identical gemini
meaning twins so this nerve has three branches to it they are the ophthalmic nerve which is
also known as v1 the maxillary nerve known as v2 and the mandibular nerve known as v3 you may
recall that there's a mnemonic for remembering how these nerves exit the skull and that mnemonic is
standing room only so opthalmic exits through the superior orbital fissure to serve the orbit and
adjacent areas maxillary nerve serve exits through the foramen rotundum the round window moves
anteriorly to serve the the deep mid-face and v3 leaves through foramen ovale the oval-shaped
window to descend down into the infratemporal fossa to serve muscles of mastication and afferently
serves the jaw region there are also branches from cervical spinal nerves which afferently serve
the head so you notice this region here of the posterior head is served by dorsal primary rami
of cervical nerves and this region here is served by branches of the cervical plexus those are the
nerve or herbs point of the neck afferents which we discussed in an earlier session the remaining
three dermatomes belong to v1 v2 and v3 so the boundary between v1 and v2 starts out at the
tip of the nose and it moves back arcing laterally till it almost reaches the eye the lateral sulcus
of the nose just above the a lie region where it ascends to the medial canthus of the eye
moves laterally across the palpebral fissure and then arcs superoposteriorly across the temporal
region all the way back to the posterior aspect of the cranium the boundary between
v2 and v3 begins at the angle of the mouth and it moves posteriorly back until almost reaching
the masseter and then it arcs nearly straight up superiorly until it runs into the boundary between
v1 and v3 so v1 v2 and v3 for the face and these these patterns are going to be clinically useful
in one particular instance and that is when an individual has a herpes zoster infection so with
with herpes zoster it's a shingles or you know reactivated chickenpox virus that is usually latent
in the in the spinal nerves but when reactivated it begins to present as itchy blisters that follow
the dermatomes and so the dermatomes of the face are good to know because one might presume to
understand the course of a herpes infection so let's take a look at some of these branches and
let's start with the ophthalmic division v1 now for the for the orbit and the eye v1 is going to
be the the star of the show in terms of nerves but for the face we're really limiting ourselves here
to the terminal branches of the frontal nerve the frontal nerve is here and it's running across the
roof of the orbit so this here is the is the eye here is lateral here is medial and medial
also works for this photograph as well that's medial and that's lateral and so this would be
a superior view of the orbit and this would be a anterior view of the orbit with the palpebrae
approximated so here's the frontal nerve moving across the roof of the orbit and it's two terminal
branches medially are the Supratrochlear nerve and laterally the supraorbital nerve and that
supraorbital nerve usually splits into a medial and a lateral branch and these are destined to
leave the the orbit and let's let's turn our attention to the anterior view here and see where
they're going so here is the super orbital nerve and it's exiting out the supraorbital foramen here
sometimes this is just a notch but here we've got a good foramen and the the supraorbital
nerve is the more robust of the two and it's the more laterally situated in this super orbital
nerve is responsible for sensory innervation of the lateral forehead the lateral aspect to
the superior palpebrae and lateral aspect of the spirit conjunctiva we also can see here the supra
trochlear nerve supratrochlear nerve is getting its name because it's exiting the skull just
adjacent to the trochlea which is a little pulley for the the superior oblique muscle there and this
super trochlear nerve is responsible for sensory innervation to the medial forehead the medial
superior eyelid and medial superior conjunctiva of the eye and it is a little more diminutive
now to AH to give you a preview of what dreams may come in the next slide we also have here the
infraorbital foramen and the infraorbital nerve traveling out the infraorbital foramen and you
might notice here is the orbit supraorbital above the orbit infraorbital below the orbit and these
two exactly in a linear plane superior to inferior but they're they're pretty close pretty close so
here is the the image that we were looking at just before so here is the lateral aspect of the eye
here is the medial aspect of the eye the bridge of the nose is running down like so super orbital
nerve super trochlear nerve and the infraorbital nerve exiting through the infraorbital foramen to
serve the skin of the superficial mid-face it'll be to the mandibular division or v3 if you recall
descends down through foramen ovale and as it comes down it's in a wonderful region that you'll
you'll come to love and appreciate known as the infratemporal fossa infratemporal fossa is where
v3 lives and from where it emanates and there are a couple of major nerves that are exiting through
here there's there's lots to be excited about as a healthcare professional especially as a dental
healthcare professional but let's say let's take these one at a time so here's the main trunk of
v3 coming down and moving off posteriorly I'm going to outline this just because it is that
cool got one branch there and one branch there you notice this originates from that main trunk
here as a fork before coming together and then moving just anterior to the ear and spreading
out over this posterior aspect to the temporal region this is known as the auricular temporal
nerve the auricular temporal nerve is going to encircle the middle meningeal branch of the
maxillary artery that's a great way to identify auricular temporal middle meningeal is coming
off the maxillary artery and it's ascending into the cranium it's one of the few vessels
that aren't of its the only vessel that isn't of either the internal carotid artery or the
vertebral artery that's entering into the cranium to to serve something and so there's that classic
anatomical relationship that we look for we'll also learn about how postganglionic branches post
ganglionic parasympathetic branches that serve the parotid gland and the parotid gland is going to be
located superficially there in the parotid fossa are carried by the auricular temporal nerve and
the the ganglion the otic ganglion is deep to the the trunk of v3 there and so it's not too
far for those fibers to hitchhike but here's the regulative oral serving that posterior
aspect of the temporal region we also have another interesting sensory nerve called the buccal nerve
some folks like to call it the long buccal so that we don't confuse it with the buccal branches of
the facial nerve but this is the afferent for the for the cheek region and here we can see the Buccinator
muscle that wonderful muscle that brings foodstuffs into the occlusal surfaces of the
teeth and then finally here we can see the mental nerve which is the terminal branch of the inferior
alveolar nerve the I A N the inferior alveolar nerve is the sensory nerve to the the mandible
and the mandibular teeth and it is a major target for an anesthetic block called an ian block for
when you're working on mandibular teeth anyways here is that a terminal branch of ia n I'm coming
out to innervate the mental region or the the chin region so that leads us to our assessment
question and that is shingles is a reactivated infection of herpes zoster or varicella-zoster
it can manifest as painful blisters along the dermatomes served by infected nerves
a shingles infection that is affecting the superior eyelid is indicative of which nerve
being involved let's see buccal nerves well buccal is a v3 branches so that's a mandibular
nerve probably not inferior alveolar nerve that's a v2 maxillary probably not v2 maxillary division
probably not now v3 maxillary division nope most certainly not ophthalmic nerve v1 yes serving
the the orbit and periorbital vicinity is the correct answer thank you very much for your time