Hello again.
This is Dr. Kingston and for this video,
I'll be discussing the innervation of the lacrimal gland.
The objective for this video,
much like the title suggests,
is to outline the parasympathetic innervation pathway
for the lacrimal gland.
Despite the gland itself being located in the orbit,
the preganglionic parasympathetics serving
the lacrimal gland actually
originate in the intermediate root of the facial nerve.
They're going to travel through
the internal acoustic meatus and then
pass through the geniculate ganglion,
which is a sensory ganglion
that is associated with the facial nerve.
So they just pass right through there without synapsing.
Inside the temporal bone though,
those parasympathetic fibers are going to branch off from
the major branch of
the facial nerve as the greater petrosal nerve,
and then they're going to head out on their own.
The greater petrosal nerve takes kind of
a convoluted pathway out of the cranium.
It ends up coming back out of the temporal bone
inside the cranial cavity
through the hiatus of the facial canal,
which is this little crack right down here.
And then it runs a short little way across
the middle cranial fossa to exit
again through foramen lacerum.
It's going to join up shortly
after that with the deep petrosal nerve,
which is carrying postganglionic sympathetics
from the superior cervical ganglion.
And together those are going to
dive into the pterygoid canal,
where they become the nerve of the pterygoid canal.
Here is the opening of the pterygoid canal.
This teeny little hole here at the bottom of your screen.
The nerve of the pterygoid canal
is going to enter in there
and it's going to travel anteriorly through the sphenoid.
Eventually it emerges into the pterygopalatine fossa,
where it will synapse with
its postganglionic partner in
the ganglion of the same name.
So that's the pterygopalatine ganglion,
which is sitting in the pterygopalatine fossa.
And that is where the synapse between the preganglionic
and postganglionic parasympathetic neurons
is going to happen.
The axons of the postganglionic neurons are then
going to hitchhike on branches of the maxillary nerve.
Now remember all the parasympathetics and the head end up
hitchhiking along with branches of the trigeminal.
Because branches of the trigeminal
go everywhere in the head.
Here specifically those parasympathetics
jump on to the zygomatic nerve,
and it's zygomatico- temporal branches.
And those are either going to carry
that innervation directly up to the lacrimal gland here,
or they're first going to take a little detour
to the lacrimal nerve,
which is a branch of
the ophthalmic division of the trigeminal nerve,
so that will come right up through there.
This appears to be variable between individuals and
investigations of how nerve fibers
travel along these nerves are
still kind of in their early stages.
So we're not sure which is more common.
And that is the innervation of the lacrimal glands.
Here's a practice question for you.
The correct answer here is C.
It won't have any effect on lacrimation.
And here's why.
So the maxillary nerve,
remember this is the second division of
trigeminal exits the middle cranial
fossa through that foramen rotundum,
comes out into what's called
the pterygopalatine fossa here.
If there was an injury to
the nerve right here at foramen rotundum,
it would not have met up with
those preganglionic fibers from the facial nerve yet.
So the flow of parasympathetics from here on
out would not be affected at all. All right.
That is the end.
Thank you very much for watching.