Transcription
This is the second tutorial on the foramina of the skull. In this tutorial, I’m going to be looking at the different structures that pass through the foramina in the skull, so the vessels and nerves that pass through these little holes. It’s quite important to know because – well, medical schools love asking about which structures pass through which foramina.
I’m assuming you’ve watched the tutorial before and it would also be quite useful if you’ve watched the tutorial on the cranial nerves or if you’ve read up a little bit about the cranial nerves. It makes it a bit easier to understand.
Looking from the outside, starting inferiorly, we’ve got the mental foramen, foramina. You can see these nerves and vessels emerging. You’ve got the mental nerves and the mental vessels that emerge from here. You’ve got these foramina just below the orbit, the infraorbital foramen and you’ve got the infraorbital vessels and nerves that come out of here. And then you’ve got these little notch here called the supraorbital notch. You can see these supraorbital vessels and nerve runs through this notch.
And then we’ve got the foramina in the orbit of the eye, the optic canal and the superior orbital fissure.
What I think I’m going to do is I’m going to switch to an intracranial view. That’s the base of the skull, wrong view. Here we go. This is the view we were looking at the previous tutorial, but now we’re going to be looking at nerves and vessels that pass through these holes.
Starting anteriorly – so this is looking from behind. If I just rotate around, this is anterior (this end) and posterior is this side – you could see here this big nerve. Now we’re looking from the front directly at the brain stem and the nerves that are emerging from it. You can see this big, fat nerve, which crosses over. This is the optic nerve.
You can see this bit here, which is the optic chiasm. This nerve passes through the optic canal. We can look that from – this is cranial nerve II and you can see it passing through this hole here, so the optic chiasm lies here and the optic nerves run out through the optic canal. That’s cranial nerve II that goes through the optic canal.
And if we look at it from the front, you can see it coming out. Also, what runs through the optic canal is the ophthalmic artery. We’ve got the optic nerve and the ophthalmic artery that run through the optic canal.
Next, we’ve got the superior orbital fissure. This is this big opening in the skull here. You can see it from the trunk. Anteriorly, you’ve got this superior orbital fissure. And if I zoom in quite a bit, you can see that quite a few little nerves emerge from this fissure. I’ll just flick back to the other view and we’ll take a look at what those nerves are. This is where knowledge of the cranial nerves is quite useful for learning what passes through the foramina.
You’ve got a couple of nerves, quite a few nerves that pass through the superior orbital fissure. You’ve got the ocular motor nerve, the trochlear nerve, the ophthalmic branch of the trigeminal nerve, the abducent nerve and you’ve got ophthalmic veins that pass through here. A lot of structures to remember, but here, we’re just going to be looking at the cranial nerves.
If I just rotate around, you can see this nerve here which is the ocular motor nerve. That runs through the superior orbital fissure.
Just remember, these are all nerves to do with the eyes. The ocular motor nerve has to do with the movement of the eyes, trochlear nerve has to do with the movement of the eyes, ophthalmic nerve is a branch of the trigeminal nerve, which has to do with sensation around the eye region and the abducent nerve is the nerve responsible for abducting the eye. These are all eye muscle and eye sensation nerves that pass through the superior orbital fissure.
If you just think of the muscles of the eye and which nerve supplies them, these are generally the nerves that pass through the superior orbital fissure.
You can see this nerve here, which emerges just medial and inferior to the inferior colliculus and winds around and passes through the superior orbital fissure. This is the trochlear nerve.
And then you’ve got this nerve, which comes right from the base of the pons. If I zoom in, you can see that. This nerve coming from the base of the pons, this is the abducent nerve and that passes through the superior orbital fissure.
And then you can see this thick trunk here. This is the trigeminal nerve. It’s got three branches. You’ve got the superior branch here, which is the ophthalmic branch, you’ve got the maxillary branch and the mandibular branch. Trigeminal nerve is cranial nerve V and the branches are labeled V1, the ophthalmic; V2, the maxillary; V3, the mandibular. You’ve got the ophthalmic branch of the trigeminal nerve passing through the superior orbital fissure. Again, it’s related to the eyes because it supplies sensation around the eye region.
Those are the four nerves which you can see passing through. Just to go over, you’ve got the ocular motor, the trochlear, the abducent nerve and the ophthalmic branch of the trigeminal. And you’ve also got ophthalmic veins which pass through the superior orbital fissure.
Next, we’re going to go down to this. We just looked at the superior orbital fissure. Just to show you again, that was this fissure here. That’s the superior orbital fissure.
And now, we’re going to be looking at this little hole here, the foramen rotundum, which you’ve got obviously on either side. That’s that little hole just inferior to the superior orbital fissure. It’s this hole here.
And what you’ve got, as you can see, you’ve got the second branch of the trigeminal, which passes through this. The foramen rotundum allows the maxillary branch of the trigeminal nerve to pass through. You can see that on either side, this branch here. The maxillary branch passes through the foramen rotundum.
And then just looking at the next branch of the trigeminal, the mandibular branch, you can see that passes through this foramen here. That’s this one, the foramen ovale. The mandibular branch V3 of the trigeminal passes through the foramen ovale.
There’s quite a lot to remember with all these different structures passing through all these foramen. I actually remembered it using really silly mnemonic, which may not make any sense, but it helps me remember stuff. The more stupid things they are, the easier they are to remember.
I had a friend called Max who was pretty fat. I thought of Max as ‘rotund’. The maxillary branch passes through the foramen rotundum. My fat friend, Max, Max is ‘rotund’. The maxillary branch passes through the foramen rotundum.
I didn’t have a friend called Mandy, but I imagined she was oval. Mandy is oval and Max is rotund. The maxillary branch of the trigeminal passes through the foramen rotundum and the mandibular branch of the trigeminal passes through the foramen ovale. Mandy is oval and Max is rotund, that’s how I remembered it. It sounds stupid, but it helped me remember. That may be useful or may just be a load of rubbish.
We’ve gone through the superior orbital fissure, the foramen rotundum, the foramen ovale and we’ve done the optic canal. Next, we’re going to keep working our way back.
Just to show you this view, the optic canal, the superior orbital fissure there, the foramen rotundum, the foramen ovale, and now we’ve got this lateral foramen, which is the foramen spinosum. What we’ve got passing through here is the middle meningeal artery. That’s that artery that lies behind pterion and is often damaged by blows to the temple.
If we just take a look – no, not that view. This is the foramen spinosum lateral to the foramen ovale. I think the best way to show you this is from the base of skull view. Let’s just see what I’m doing. I’ve got the skull here, I’m just rotating it so you can see from the bottom. Just to orientate you a bit, you’ve got this hole here, the foramen ovale. Remember, Mandy is oval, so the mandibular branch of the trigeminal passes through there (which you can’t see on this side, but I’ve put it in here). There’s the mandibular branch of the trigeminal passing through there. That’s the foramen ovale.
And then lateral and posterior to that, you’ve got the foramen spinosum. You can see the middle meningeal artery going in there. Let’s just rotate it around so you can have a look at that. We rotate this skull upside-down and we’re looking at the inferior view. You’ve got the foramen ovale, the foramen spinosum and you’ve got the middle meningeal artery passing through there.
Just while we’re in this view, you can see just posterior to this, you’ve got the carotid canal. It’s called the carotid canal because the internal carotid artery passes through this little hole and then it joins the Circle of Willis at the base of the brain. You can see this complex arterial supply to the brain.
If we just follow there, we’ve got the carotid, common carotid here and it bifurcates into the external carotid with all its multiple branches (I’m going to do a tutorial on this) and you’ve got the internal carotid, which passes through the carotid canal into the brain and it joins here with the circle of Willis. That passes through the carotid canal, which is here. Obviously, you’ve got that on either side. Try to ignore these labels, they’re just put up here for me to get the right display the rest of the carotid canal with the internal carotid and the middle meningeal artery passing through the foramen spinosum.
Coming to the posterior cranial fossa now, so all these bit here, we’ve now got the internal auditory meatus, the jugular foramen and the hypoglossal canal.
The internal auditory meatus has two cranial nerves passing through it. And if you look at the origin of these cranial nerves, you can see them at the bottom of the pons and laterally. We’ve got the vestibulocochlear nerve and the facial nerve, so cranial nerves VII and VIII.
Cranial nerve VII, which is the facial nerve (so you can see it), it’s slightly anterior to the vestibulocochlear nerve, which is this one here. They run through the internal auditory meatus.
Also passing through the internal auditory meatus, but not on this model here is the labyrinthine artery. You’ve got the facial nerve, the vestibulocochlear nerve and the labyrinthine artery going through the internal auditory meatus.
And again, it’s quite logical if you think about it because the vestibulocochlear nerve has to do with hearing and balance and ‘internal auditory meatus’ kind of gives away the fact that it’s a foramen to do with hearing – auditory, you’ve got the vestibulocochlear nerve passing through that. It’s quite logical if you think about these things.
Just inferior to this, we’ve got the jugular foramen. We’re just looking at this view again. We’ve just done the internal auditory meatus, which is up here and now we’re looking at the jugular foramen, which is here. And then you’ve got the hypoglossal canal further down, which is the next one I’m going to talk about.
The jugular foramen has loads of structures that pass through it. It’s called the ‘jugular foramen’ for a reason, because the internal jugular passes through it.
I’ve just flipped back to the base of the skull view. You can see what I’m doing here, base of the skull. That was the carotid canal. Posterior to that and slightly lateral, you’ve got the jugular foramen. You could see all these structures passing out, so all these nerves passing out (which you saw on the other view). You’ve got this vein, the internal jugular vein, which passes through the jugular foramen, hence the name.
I’ll just rotate it around the bit and you can see that. Again, try to ignore all these labels and just look where my mouse is pointing. you’ve got the internal jugular vein passing up here coming off the superior vena cava and then passing through the jugular foramen into the inside of the skull.
Flicking back to the view from inside just so you can have a look at what we’re looking at, we’re looking at the jugular foramen here. I’ll just zoom in a bit again. I’ll just talk about the nerves.
We’ve got a couple of nerves that pass through the jugular foramen. We’ve got the 9th, 10th and 11th cranial nerves. These nerves emerge from the medulla. The most superior one, we’ve got the 9th nerve, the glossopharyngeal nerve, then we’ve got the vagus nerve and then we’ve got this nerve, which goes for both this foramen and the foramen magnum – so these three nerves which emerge from the medulla. The glossopharyngeal nerve, the vagus nerve and the accessory nerve, so cranial nerves IX, X and XI pass through the jugular foramen.
That’s four structures to remember. You’ve got cranial nerves IX, X and XI and you’ve got the internal jugular vein. Just having a look at that again from the base, you’ve got the internal jugular vein and you’ve got all these nerves coming out. That’s the jugular foramen.
Next, we’re going to be looking at this, the hypoglossal canal. [Inaudible 00:07:48] guessing what passes through that, but just having a close look, if I rotate around to the front, you can see this nerve here, which is the 12th cranial nerve emerging ventrally on the brain stem, on the medulla. The hypoglossal nerve passes through the hypoglossal canal, so this foramen here.
You can see that nerve from the base of the skull view. You’ve got the jugular foramen here, you’ve got the carotid canal here with the internal carotid, you’ve got the jugular foramen with its three nerves and the internal jugular and you’ve got the hypoglossal canal where the hypoglossal nerve emerges, the 12th cranial nerve.
Just to finish up, obviously, this big hole is the foramen magnum. Here you’ve got the beginning of the spinal cord at the junction where the brain stem meets the spinal cord passing through here. You’ve got vertebral arteries passing through here and you’ve got the spinal roots of the accessory nerves.
Remember, the accessory nerve, cranial nerve XI passes through the jugular foramen and also through the foramen magnum. It’s got two roots. You’ve got the roots up here and the spinal roots, which pass through the foramen magnum.
That’s the foramen magnum. Obviously, the spinal cord passes through there and the brainstem, the vertebral arteries and the spinal roots of the accessory nerve.
And just one more thing. If you remember this foramen here from the previous tutorial, the foramen lacerum, no structures pass through this. In life, it’s filled with cartilage.
Okay! I know that was a long tutorial, but hopefully, you now know what vessels and nerves pass through the different foramen and you have a good idea of the different foramen in the skull now.