Hi let's talk about the extraocular muscles. In this video we'll discuss the attachments actions
and innervations of the extraocular muscles. The extraocular muscles are sometimes referred to as
extrinsic eye muscles. These are muscles found outside of the eye which largely affect either the
movement of the eye or the superior eyelid. Their proximal attachments are either within bone of
the orbit or on the common annular tendon which is found at the posterior aspect of the orbit.
Their distal attachments are largely on either the sclera or in the case of levator palpebrae
superioris on the superior eyelid. And most of these muscles therefore are going to affect
gaze or the direction that the eyes are pointed. Their actions can sometimes be rather complex
and that's the result of orbital asymmetry. Recall that the orbit is a pyramid, with its long axis
directed posterior medially. What that means is that some muscles such as, let's consider the
superior rectus muscle here, when it contracts it's going to have both a posterior vector
and a medial vector. And so often times the rectus muscles will adduct or move the gaze
inwards. Because of that we'll see that the oblique muscles superior and inferior oblique will have
lateral components to their vectors which will abduct gaze.
Most of the extraocular muscles are innervated by cranial nerve 3 which is the oculomotor nerve
aptly named. The superior oblique muscle is innervated by the trochlear nerve ,and
the lateral rectus by the abducens nerve. So let's start with levator palpebrae superioris
which is kind of the odd duck in that it's the only extraocular muscle which does not
attach to the sclera. It runs from the apex of the orbit down to the superior tarsal plate.
When activated it elevates the upper eyelid, it's innervated by
the oculomotor nerve. Now there is also a tiny component of smooth muscle behind its aponeurosis
part of that tarso fascial layer that's known as the tarsal muscle or superior tarsal muscle.
This muscle is under autonomic control and when stimulated by the sympathetic
component of the autonomic nervous system these are fibers from the superior cervical ganglion
this smooth muscle contracts and helps to maintain the patency of the
palpebral fissure by elevating that superior eyelid.
The remainder of the muscles that we'll discuss will all attach to the sclera and move the eye.
So the first is the superior oblique muscle this has an attachment at the apex of the orbit. And
it has a distal attachment on the superior sclera of the eye but it has a rather unique pathway
to get there. So let's let's look at this illustration we can see the belly of the superior
oblique muscle runs out lateral I'm sorry runs out medial to the superior rectus muscle and its
tendon goes through a little cartilaginous loop known as the trochlea same name as the nerve that
innervates it and it wraps around like so. So here we can see the trochlea and we can see that tendon
of the superior oblique muscle running out and attaching to the sclera of the eye.
So it is superior to the medial rectus muscle and medial to the superior rectus muscle. Now when the
superior oblique muscle contracts that tendon is going to pull the eye that way and as a result of
that it's going to abduct and depress gaze. So gaze is going to slightly go outwards and downwards.
Now the superior oblique muscle also has an element of intorsion to it. Intorsion is a rotation
of the eye in particular it's a rotation of the superior pole of the eye medially. The superior
oblique muscle is the only extraocular muscle innervated by the trochlear nerve and the fact
that its tendon goes through the trochlea is very consistent with allowing you to remember that fact.
The next muscle we will discuss is the superior rectus muscle. The superior rectus muscle is
found just inferior to levator palpebrae superioris. Its proximate attachment is on
the common annular tendon at the postero medial aspect of the orbit. Its distal attachment
is on the sclera at the superior pole of the eye. When the superior rectus muscle contracts
it's going to both elevate and adduct the eye, so the eye goes upwards
and inwards, where gaze goes upwards and inwards. This is because again the orbit is asymmetrical.
It's going to have that component as well as that vector component to the force. The superior rectus
muscle like many other extraocular muscles is innervated by cranial nerve 3 the oculomotor.
Next is the medial rectus. The medial rectus also originates from the common annular tendon
and it's going to insert on the sclera of the medial side of the eye. The medial rectus muscle
owing to the fact that the asymmetry of the orbit doesn't affect its pathway is going to adduct gaze
or move it medially. Here we can see that this is medial because we can see the lacrimal lake.
The medial rectus muscle is innervated again by cranial nerve 3 oculomotor. Next we
have the lateral rectus. The lateral rectus like the medial rectus takes its proximal attachment
from the common annular tendon, and its distal attachment is at the lateral aspect of the sclera.
Again its actions are not confounded by the shape of the orbit. When the lateral rectus muscle pulls
gaze is going to abduct or move laterally. The lateral rectus muscle is innervated by the
abducens nerve. One way of remembering this is that the abducens nerve abducts gaze, lateral rectus.
Next we have the inferior rectus muscle. The inferior rectus muscle
like all the other rectus muscles takes its proximal attachment from the common annular tendon.
Its distal attachment is on the inferior pole of the sclera, and when activated it is going to
depress and adduct gaze. It also will be involved in extortion. Extortion is the movement of the
superior pole of the eye outward or the inferior pole of the eye inward.
The inferior rectus muscle is innervated by the oculomotor nerve cranial nerve 3.
So both superior and inferior rectus muscles are going to adduct
gaze. Let's take a look at the inferior oblique now. The inferior oblique muscle takes its proximal
attachment from the orbital surface of the maxilla, its distal attachment is kind of
lateral and inferior on the sclera, and when it pulls when it activates it's going to abduct
and elevate gaze so the eye will move outwards and upwards.
The inferior oblique muscle is also going to be involved in extortion. So one thing that
that I like to think about is that rectus muscles,
so we're talking about superior and inferior rectus muscles, are going to be adductors.
Oblique muscles
are abductors. So obliques = abduct. Also superior rectus and superior oblique muscles lead to
intorsion, whereas inferior oblique in inferior rectus muscles lead to extortion. The inferior
oblique like most of the other extraocular muscles is innervated by the oculomotor nerve.
So we've discussed the extraocular muscles their proximal and distal attachments
their actions as well as their innervations. This is your summary slide. Thank you for your time