Neuroanatomy: #1 Extraocular muscles!

Any medical students reading this probably just let out an audible groan. Let me take a moment to join you… *groans*.

Neuroanatomy is, at the present moment, running my life. Thankfully I do have an interest in it and I do want to learn but even then spending hours upon hours in the anatomy lab gets a little tiresome.

SO!

With that in mind I have decided to share and share alike my resources for neuroanatomy for any medical students dropping by who this might be relevant to. Sharing is caring people, and it might save us all a little time in the lab.

Without further ado I present to you, a brief overview of the extraocular muscles. This might be a bit of a strange topic to launch straight into but it is one that I am confident with and so wanted to share.

Extraocular muscles:

The extraocular muscles are responsible for the movements of the eyeball. There are 6 (7 if you count the lovely levator palpebrae superioris which moves the eyelid) and they are:

Superior oblique
Inferior oblique
Lateral rectus
Medial rectus
Superior rectus
Inferior rectus
(Levator palpebrae superioris) 

What do they look like I hear you ask. Well let me refer you to the following beautiful diagrams

Now these muscles are very difficult to see in an actual specimen and are much more easily identified on schematics and in plastinated models. Initially it can be difficult to know which is which but once you have identified them the first time it is becomes a lot easier and their names help substantially.

Let’s hear a little bit more about these muscles:

Superior rectus: originates from the common tendinous ring situated deep in the orbital cavity, it attaches to the top of the eyeball.

Inferior rectus: is in the same plane as superior rectus and has the same origin. It attaches to the base of the eyeball and is difficult to see unless superior rectus is dissected away.

Medial rectus: On the medial aspect of the orbit, also originates from the common tendinous ring. It attaches to the medial aspect of the eye ball

Lateral rectus: Same as the medial rectus but on the lateral side

Superior oblique: originates from the common tendinous ring and passes anteriorly on the medial wall of the orbit, it becomes tendinous and it’s tendon passes through a structure known as the trochlea. By passing through the trochlea which acts as a pulley system the tendon turns 90 degrees to insert on the posterior lateral aspect of the eyeball.

Inferior oblique: does NOT originate from the common tendinous ring. It instead originates from the maxillary bone. The muscle belly passes up under the eyeball before becoming a tendon and inserting on the inferior posterior aspect of the eyeball.

We’ll quickly cover the innervation of these muscles and we’ll in a later post/ a revision to this post look at the action of these muscles. The reason I’m delaying this is because the axis of the orbit is different to that of the eye so the action of the muscles, particularly the obliques, may not be as expected and I feel I can best explain this with a video which I need to film.

So!
The innervation of these muscles is very simple. Remember this: Oculomotor (CN 3) does all except LR6 SO4.
LR6 = Lateral rectus is innervated by cranial nerve 6 which is abducens nerve
SO4 = Superior oblique is innervated by cranial nerve 4 which is the trochlear nerve. (Incidentally another way to remember this is that the superior oblique passes through the pully called the trochlea and is innervated by the trochlear nerve)

Thanks for reading, hope you are somewhat enlightened! I promise to cover the action of the muscles soon!