Hi let's talk about the palpebri. In this video we'll discuss the components of the palpebri also
known as eyelids and their associated structures. So palpebri is completely synonymous with eyelids.
The singular would be palpebra. These are layered structures which cover the anterior portion of the
orbit. They're also very dynamic so they're mobile as well. The most superficial layer of a palpebra
is the skin, and this is going to be contiguous so this wraps around and meets with the deepest layer
which is the palpebral conjunctiva, we'll discuss the conjunctiva in a moment. And so
where these two meet there are follicles for eyelashes
and associated glands. And the remainder of the eyelid is sort of sandwiched between the two
and let's take a look at some of those layers. So deep to the skin we have the subcutaneous layer.
Deep to the sub-q we have a portion of a sphincteric muscle which surrounds the orbit it's
known as the palpebral part of the orbicularis oculi muscle which I will outline there.
Deep to the palpebral part of orbicularis oculi
is the torso fascia layer which we'll discuss in great detail, this consists of things like
the orbital septum the aponeurosis or the tendon for this levator palpebri superioris muscle
as well as the superior tarsal muscle associated with that tendon the superior tarsal plate
and other features that we can't see in this particular illustration. So as I've
said previously let me erase this the deepest layer of the palpebra is that palpebral part
of the conjunctiva or the palpebral conjunctiva. The conjunctiva is a mucous membrane
which is going to line the palpebri and cover the anterior surface of the eye.
Between the palpebral conjunctiva and the bulbur conjunctiva is a space so they're
usually in pretty close contact with one another, known as the conjunctival sac. And the conjunctival
sac is the space into which tears are secreted and conveyed through the lacrimal system. It's also
by the grace of this conjunctiva that any foreign objects be they intentionally entered to the eye
such as a contact lens or unintentionally such as debris they can't
move behind the eye because the conjunctiva forms a barrier there to prevent movement posteriorly.
So the orbicularis oculi muscle found deep to the skin and the subcu
is a very impressive muscle of facial expression. I'll outline it there in the
cadaveric image. So breaking down that name orbicularis oculi muscles have different naming
conventions and sometimes they're named for the directionality of their fibers. Orbicularis muscles
have their fibers going circumferentially like this so they almost form a sphincter.
Oculi is of the eye so this is the sphincteric muscle of the eye or what we would call
the palpebral fissure which is the space between the palpebrae.
This is a tri-part type muscle. There is an outer orbital part. So
that orbital part is everything between these two circles.
The orbital part shuts the palpebral fissure tightly. It's voluntarily controlled. There's a
palpebral part which is everything inside this inner circle and that's right upon the palpebri.
The palpebral part is used for blinking and it's involuntarily controlled. There's also
deep to these a lacrimal part. That lacrimal part when it contracts squeezes the lacrimal sac which
is a part of the lacrimal apparatus and that serves to create suction when it releases so it
draws tears across the lacrimal sac towards the medial canthus or the medial portion of the eye.
All three parts of this muscle are innervated by the facial nerve which is cranial nerve
number 7. The facial nerve has a variety of targets and it's best known for its namesake.
It's the innervation for the facial muscles or the muscles of facial expression.
So deep to orbicularis oculi palpebral part is the torso fascial layer.
The torso fascial layer is quite diverse and it gives support and structure to the palpibri.
So coming off of the orbital rim so here we can see the periosteum there is an extension of that
periosteum known as the orbital septum. That orbital septum is going to separate
the orbital fat from the structures of the palpebri.
There will be one inferior as well so here we can see the orbital septum,
orbital septum, all around orbital septums.
That orbital septum is going to blend in to the tarsal plates. So here is the superior tarsal plate
there's one in the superior palpebra there's also one in the inferior palpebra. These tarsal
plates are going to give shape and support to the eyelids so these are the reasons why if you're
ever the child who turned their eyelids inside out you know that supports that particular arrangement.
Also at the medial and lateral canthi or angles of the eye we have the medial
palpebral ligament and the lateral palpebral ligament these are attaching to both superior and
inferior palpebri. We also have the aponeurosis and aponeurosis is a sheet-like tendon for an
extra-ocular muscle known as levator palpebri superioris. Levator palpebri superioris is the only
extraocular muscle that does not affect the action of the eye. It affects the action of the superior
palpebra. It comes in and attaches to that superior tarsal plate and when that muscle contracts the
superior eyelid is elevated. You can also see in this illustration that there is a little slip of
muscle here. This is smooth muscle known as the tarsal muscle sometimes superior tarsal muscle.
That is also attached to the superior tarsal plate. It is autonomically controlled so it's
under sympathetic innervation and when it's stimulated sympathetically
it helps to keep the upper eyelid raised. And then finally we have tarsal or
meibomian glands, these are modified sebaceous glands so oil glands and they secrete a substance
known as meibum. Meibum gets secreted along the edge of the palpabri, both inferior and superior.
And it helps to maintain the tears so it helps to prevent them from evaporating away.
So we've discussed the various layers of the palpabri, the skin, the sub-q,
the conjunctiva, both palpebral and bulbur, palpebral part of orbicularis oculi muscle,
the tarso fascial layer. This is your summary slide, thank you for your time.