Hi let's talk about the lacrimal system. In this video we'll discuss the components of
the lacrimal system, detailing the pathway of tears from the lacrimal gland to the nasal
cavity. We'll also distinguish between the somatic and autonomic innervation of the lacrimal gland.
So the lacrimal system consists of the lacrimal gland and the entirety of the pathway of tear
conduction to the nasal cavity. So this process begins in the superior lateral portion of the
orbit, so the lacrimal gland is found adjacent to the lacrimal fossa of the frontal bone. It secretes
tears or lacrimal fluid into the conjunctival sac, that's the space between palpebral and bulbur
conjunctiva. And those tears are conducted toward the medial canthus or angle of the eye. Now along
the palpebri ,we have tarsal glands also known as meibomian glands which secrete meibum
which is an oily substance. This helps prevent the tears from spilling out by creating a
hydrophobic barrier, and this also aids in the prevention of evaporation of the tears. So those
tears have nowhere to go but that medial canthus, and this area here
of the medial campus where the tears accumulate, is known as the lacrimal lake. So tears accumulate
in that area, and they are absorbed through tiny little pores or puncta in both the superior and
the inferior eyelids, and then conducted via canaliculi out to the lacrimal sac.
This lacrimal sac is deep to the lacrimal part of orbicularis oculi I think of it like a little
squeeze ball. So when the muscle contracts it squeezes that and when the muscle relaxes it,
creates a vacuum sucking the tears into the lacrimal sac. This is considered a dilation of
the proximate part of the nasolacrimal duct which is a pathway down into the inferior nasal meatus.
So that's the space that's underneath this inferior nasal concha here. So your tears move
from the lacrimal gland, across the conjunctival sac, into the lacrimal lake, into the lacrimal sac
through the nasolacrimal duct, and into the inferior nasal meatus of the nasal cavity.
It's important that we differentiate between somatic versus autonomic innervation of
the lacrimal gland. The lacrimal gland somatic information is complements of the lacrimal nerve.
The lacrimal nerve is a small branch of v1 which is the ophthalmic division of the trigeminal nerve.
So in this illustration we can see the trigeminal nerve here,
and there is v1 which is the ophthalmic division, v2 the maxillary, and v3 the mandibular division. So
v1 is going to be a major player in terms of the orbit and eye. And here outlined in brown we can
see that lacrimal nerve heading out to somatically and afferently innervate the lacrimal gland and
surrounding areas, so not only will it conduct somatic afferent fibers back
from the lacrimal gland but also from the conjunctiva and the surrounding skin area.
The autonomic innervation of the gland is from a completely separate source.
And to understand that let's turn our attention to this illustration on the bottom.
Here we're looking at a lateral view of the skull and right here
going through a rather large osseous canal is the facial nerve, cranial nerve 7. The facial nerve
is what supplies the preganglionic parasympathetic fibers. You can see them heading out here, this is
along a nerve called the greater petrosal, and it's met with a nerve called the deep
petrosal which is conducting sympathetic fibers from this superior cervical ganglion up along the
internal carotid artery. So sympathetic fibers from the internal carotid plexus from that superior
cervical ganglion meet preganglionic parasympathetic fibers to form a nerve.
This is called the nerve of the pterygoid canal. This heads out towards a ganglion there.
So this is a peripheral parasympathetic ganglion known as the pterygopalantine
ganglion. An older name for it is sphenopalatine. And it's found in the pterygopalatine fossa.
That area that's contiguous with the orbit by means of the inferior orbital fissure. So
the preganglionic parasympathetic fibers from the facial nerve will synapse there and they hitchhike
out along v2 branches. So here we can see going out to the orbit. We turn our attention to this
illustration up here we can see there's v1 there's v2. The v2 fibers have grabbed those postganglionic
parasympathetic fibers and deliver them out to the lacrimal gland. So with parasympathetic stimulation
we have the enhancement of lacrimation so the rest and digest creates tears.
Sympathetic stimulation again complements of this superior cervical ganglion of the sympathetic
chain is going to inhibit lacrimation and it will also lead to local vasoconstriction. So we
have discussed the lacrimal system, the pathway of tears from the lacrimal gland to the nasal cavity,
and we've also discussed somatic innervation via the lacrimal nerve, and autonomic innervation
via the facial nerve, the pterygopalatine ganglion, as well as v2 hitchhiking, and the sympathetic
innervation of this gland. This is your summary slide, thank you very much for your time