Hi everyone.
This is Dr. Kingston,
and in this video I'll be talking
about the innervation of the orbit.
The objective for this video is to
identify all of the nerves that provide
motor, sensory, and autonomic innervation
to the orbit and its contents.
We're going to start off with the big one.
The optic nerve is the largest supplying the orbit,
and it's carrying special sensory innervation.
It enters the orbit through the optic canal,
which passes through the sphenoid,
just anterior to the sella turcica.
So here would be the sella turcica.
There's the optic canal.
And we can see that coming into the orbit right there.
You can see the optic nerve here as it
enters through the optic canal into
the apex of the orbit and then travels
anteriorly a small way to meet the posterior eyeball.
The nerve itself is composed
of axons from ganglion cells from the retina.
These are going to pierce the sclera to form the nerve,
and then they carry visual information back to the brain.
The retina is covered in much more detail in the video,
going over the layers of the eye.
So please check that one out if you have not already.
From special sensory, we'll move
right on to somatic sensory.
Somatic sensory innervation to the orbit is
carried by the ophthalmic division
of the trigeminal nerve.
And you can see here that the orbit is nicely
subsumed into the green V1 territory here.
The ophthalmic nerve enters into the orbit
like most things that we've seen so far.
So through that superior orbital fissure.
Once it's there, it gives off its branches.
Nasociliary, frontal, lacrimal.
And I put them in this order specifically
so you can remember NFL,
but we're going to look at them in
a slightly different order.
Anatomically speaking, it makes
the most sense to look at the frontal nerve first.
It is the largest branch of the ophthalmic nerve.
And it is also very
superficial in the orbit here as you can see.
So here is where it is running.
Right there.
It is going to enter
the orbit here through that superior orbital fissure.
And it is going to course very superficially, as I said,
over the superior surface of
the superior rectus and
levator palpebrae superioris muscles.
It's going to dive fairly close to
the medial aspect of the orbit.
And as it approaches about midorbit here it's
going to start to give off its own branches.
The two that we are really going to focus
on for this course here are number one,
the supratrochlear, which is going to continue
out of the orbit by passing superior to the trochlea.
So here's superior oblique and here's that facial sling,
that trochlea, that it wraps around.
Supratrochlear nerve heads up over the top of
that onto the skin of the face where it's
going to innervate the skin on
the medial forehead and the medial superior conjunctiva.
The rest of the frontal nerve
continues as the supraorbital nerve.
And the supraorbital nerve is going
to exit the orbit here through either
the supraorbital notch or the supraorbital foramen,
depending upon your anatomy
This is pretty variable by person.
As it exits onto the face,
it is going to innervate the mucosa of the frontal sinus.
So I should say that happens
before it goes out onto the face.
And then the skin of the lateral forehead
and the lateral superior conjunctiva.
The lacrimal nerve is much
smaller than the frontal nerve,
is going to travel along the lateral aspect of
the orbit straight up to the lacrimal gland,
which it is bringing somatic sensory innervation to.
The nasociliary nerve sits
slightly deeper than the other branches and
it's easiest to see after
reflecting the superior oblique muscle.
So that's what's been done in this image.
It travels medially in the orbit and it
gets off the long ciliary nerve
fairly early in its course.
The long ciliary carries somatic sensory from the eye.
And it's also carrying
some postganglionic sympathetics to
the dilator pupillae muscle.
All right, back to that main stem of the nasociliary,
then. As we see it
traveling along the medial wall of the orbit,
we get the anterior and posterior ethmoidal nerves.
These are going to leave
the orbit through the anterior and
posterior ethmoidal foramina and head into
the ethmoid air cells where
they're going to provide somatic sensory.
The final branch of the nasociliary and
the orbit then is the infratrochlear nerve.
So we saw the supratrochlear nerve that
exited the orbit by going superior to the trochlea,
this one's gonna do just the opposite.
It goes out underneath that trochlea onto the face where
it's going to innovate
the conjunctiva, f the skin and the eyelids,
the lacrimal caruncle and sack,
and the side of the nose.
Somatic motor innervation is
carried into the orbit by three cranial nerves.
These are the oculomotor nerve,
the trochlear nerve, and the abducens nerve.
And they are all going to enter the orbit,
orbit through the superior orbital fissure.
So I talked briefly about
these nerves in the extra ocular muscles video,
but we're going to take a little bit deeper dive
into the pathways of each of these here.
We'll start off talking about
the trochlear and abducens nerves,
since they're pretty simple.
The trochlear nerve exits the brain stem,
travels anteriorly through the wall
of the cavernous sinus,
goes through the superior orbital fissure.
It's going to pass through that fissure fairly superiorly.
And then it just takes a short jump
over to the superior oblique,
which it usually reaches from a superior angle.
The abducens nerve travels directly
through the cavernous sinus to
reach the superior orbital fissure.
It passes through laterally and
you can find it here on the lateral side of the orbit,
coming up to the lateral rectus muscle,
which it usually approaches from the medial side.
The oculomotor nerve has a little bit more to it.
So this one innervates five out of
the seven extra ocular muscles.
It is highlighted here in pink.
And we can follow its superior division up here towards
innervating the levator palpebrae superioris
and the superior rectus.
And we can also follow its inferior division
down here to inferior rectus, inferior oblique.
And it would also innervate medial rectus,
which is not shown on this cartoon.
In addition to doing a lot of
the heavy lifting for
somatic motor innervation and the orbit.
The oculomotor nerve is also carrying
some additional types of innervation,
specifically some parasympathetics, which
you can see kinda indicated by the orange here.
So let's take a look at those.
The parasympathetics carried by
the oculomotor nerve are
headed for two muscles in the eye,
the sphincter pupillae and the ciliary muscle,
both of which are sitting right up here.
The preganglionic parasympathetic neurons
originate in the oculomotor root and
their axons are going to travel down
the oculomotor nerve and into the ciliary ganglion.
In that ganglion they're going to
synapse with their postganglionic partner.
And then the axons from
those partners are going to travel up
the short ciliary nerves and into the eye.
And because we're talking about parasympathetics,
it's not a bad idea to dive right into the
sympathetic innervation for the orbit right now as well.
Now, even though I'm going to be
using the same illustration here,
I am no longer talking about the oculomotor nerve.
So sympathetics in the head,
we're going to find coming up here on this vessel here,
which is the internal carotid and then its branch,
the ophthalmic artery that enters into the orbit.
What's important to remember about
sympathetics traveling in the head and neck
is that they don't form
nice fat nerves like we see here for other things.
They are going to form a plexus over vessels.
So we call these perivascular plexuses.
And they do this on the internal carotid,
up into the skull,
into the cranium, and also
out onto that ophthalmic artery.
Right now we're talking about this pathway which
leaves the internal carotid artery
and it is going to travel down into the ciliary ganglia.
Now remember, sympathetic fibers that have made
it this far up into the head have already synapsed.
So to get here,
they first had to leave the spinal cord,
the preganglionic neuron then would travel
into and up the sympathetic chain
to the superior cervical ganglion.
It would synapse there.
And then the post- ganglionic axon is what
is going to be writing these perivascular plexuses.
So we are seeing a postganglionic sympathetic axon,
cluster of axons coming off
that perivascular plexus traveling
through the ciliary ganglion and then
onto those short ciliary nerves to reach the eye.
Additionally, we have some postganglionic sympathetics
from the same perivascular plexus here that are
going to jump up onto the ophthalmic artery
and then off onto the nasociliary nerve and its branch,
the long ciliary nerve.
And those will also approach the eyeball here.
These are specifically for
the dilator pupillae muscle.
If I flip back here, these,
this pathway here for the short ciliary muscles,
these are going to intraocular vessels.
So these are what would dilate
or constrict the blood vessels in the eye.
So the ciliary ganglion,
as we've seen in these last couple of slides,
have a couple different types
of fibers moving through it.
We started off with the pre- and
postganglionic parasympathetic shown here in orange.
So we have our preganglionic coming down and
our postganglionic making up
most of this ganglion, right?
So this is mostly going to be
cell bodies and synapses around them.
And then the postganglionic parasympathetics
traveling out through the short ciliary nerves.
We also saw some postganglionic sympathetics leave
that perivascular plexus travel through the ganglion
without synapsing and also
ride those short ciliary nerves.
This makes it look a little bit more like
a traffic interchange then a ganglion.
Now, we're going to add in
some somatic sensory fibers as
well to really make it look like traffic jam.
These are coming from the nasociliary branch of V1.
And just like the sympathetics,
they don't do anything here.
They're just passing through.
They are heading down
to the inferior division of the oculomotor nerve.
And they're going to be supplying
somatic sensory innervation to these muscles.
So our inferior rectus, inferior, oblique,
and medial rectus as well as to
the tissues in the inferior orbit.
So there's a lot going on here in
this tiny little ganglion.
We find not only parasympathetics,
but also axons from
sympathetic neurons and somatic sensory neurons.
And that is going to bring us to the end.
Let's do a practice question.
The correct answer here is C. There are
no somatic motor fibers passing through that ganglion,
but there are all the other kinds listed here.
And that is the end.
Thank you for watching.