Okay, we're going to talk about triangles of the neck and answer the questions, what is the deal with anatomists and geometry and what are the borders and contents of the posterior triangle and what are the borders, sub-triangles and contents of the anterior triangle? Hello everyone, my name is Dr. Morton and I'm the noted anatomist. So why do we care about triangles? Well, triangles facilitate descriptions of neck anatomy and they also help us more easily identify structures. What do I mean by this?
Well, here's a map of the United States and let's use Google Maps and let's zoom in and zoom in and zoom into the great state of Utah and zoom in a little bit more. We're like, hey, look at this great little part. We're in central Utah. And someone asks a question and says, hey, what's this highway right here? Well, on this handy dandy map, I take a look at that blue thing and I'm like, oh, that's Interstate 15 or the I-15.
Done and done. But what happens if the map is not labeled? And someone says, hey, what's this highway right there? Now, I don't have the label on that highway, so I have to use other features on this map to identify that.
So, I look over into the west. I'm like, well, that's the Great Salt Lake, and oh, there's the Wasatch Mountains. What is the only interstate with a major interstate highway going north through between those two structures? That's Interstate I-15.
I know that. So, you use readily identifiable landmarks. big lake and mountains to help you identify smaller landmarks within.
So here we have a picture, some anatomy of the head and neck. And someone says, hey, what's this artery right there? And you're like, oh man, this isn't labeled.
What do I do? So let's look for our big lakes. We got the digastric muscle, posterior belly and digastric muscle, anterior belly.
And then we have here is the mandible. So then we know that's in the submandibular triangle. That's definitely the facial artery. We use...
readily identifiable landmarks to help identify smaller landmarks within. So the sternocleidomastoid muscle becomes one of our big mountain ranges or lakes that helps us divide the neck into two triangles, the posterior triangle and the anterior triangle. So here's this lateral view of the neck and you're like, there's the sternocleidomastoid.
So behind it is the posterior triangle and in front of it is the anterior triangle. That becomes one of our big mountain ranges that we recognize, sternocleidomastoid. Well, let's go to the posterior triangle. Its borders are the sternocleidomastoid, traps, and clavicle. And the roof and floor are the deep, investing, and prevertebral fascias.
Here we have a lateral view. We find the posterior border of the sternocleidomastoid, anterior border of the traps, and the clavicle. And shing!
There is the posterior triangle of the neck. So similar here, we rotate the head. And then we zoom in, we're like sternocleidomastoid, clavicle, traps, there's our posterior triangle of the neck.
There is this region within. And so the borders are also the deep investing fascia. So we then outline that and there's our posterior triangle.
So the roof of the posterior triangle is deep investing fascia. Now let's take a scalpel and cut along that and open it up. So you see the cut edge of the deep investing fascia and the floor.
of the posterior triangle is the pre-vertebral fascia of the neck. So let's do that again. That was fun.
Here's our sternocleidomastoid and the traps. So what's in between them? That's the posterior triangle of the neck. So the roof is this deep investing fascia. So now if we take a scalpel there and there and cut, we then see the deep investing fascia is cut.
The floor is the pre-vertebral fascia, in this case surrounding our scalene muscles. The contents of the posterior triangle are as follows. What pierces the deep investing fascia are these cutaneous nerves from the cervical plexus and our external jugular vein. And the floor has a number of other structures we're going to cover. So let's first do this piercing the deep investing fascia.
So there's our deep investing fascia. And there, right in the posterior midline, posterior part of the sternocleidomastoid, we have these cutaneous branches of the cervical plexus that branch out. That's called the herbs point of the neck. And...
I'll talk about all those in a separate video. And then we also have the external jugular vein piercing as well in that area. We're also lining that as superficial cervical nodes. So in this cross section, we see right there between the two as opposed to your triangle. So watch as those nerves come up between our scalenes and pierce the deep investing fascia and go out into the skin.
Now the floor of this. is as follows. Well, there's one of the muscles we see in the floor of the posterior triangle is called the omohyoid. And the omohyoid is going to divide this posterior triangle into an upper triangle called the occipital triangle, because that's where the occipital artery is found. And then below it is the supraclavicular triangle, where we have the suprascapular artery and transverse scapular artery in that area.
Let's now take a look again. There is the prevertebral fascia forming the floor, and then... Skimming right superficially across it is the spinal accessory nerve or cranial nerve 11, which is going to innervate our SCM and the traps. We also have the transverse cervical artery and the suprascapular artery. Now, if we go deeper and remove that prevertebral fascia, we see our splenius capitis, levator scapulae, posterior scalene, middle scalene, and anterior scalene muscles.
Additionally, between our middle and anterior scalene, we have the cervical plexus, which are the spinal roots from C1 to C4, and the brachial plexus, which is from C5 to T1. All of those plexuses, C1 to T1, are all exiting the neck between our anterior middle scalene. So if you then see muscle and or a nerve in the neck coming between, you can now use these as landmarks to determine what is what. Additionally, the subclavian artery comes out between our anterior middle scalenes and the subclavian vein comes out in front of. That was fun.
Let's do it again. Let's zoom in. So there is our anterior and our middle scalenes. So there has become our mountain range and our Great Salt Lake.
So between that, we know that must be a branch of the cervical plexus. Specifically, that's the phrenic nerve. And then we know that that's the brachial plexus and below that's the subclavian artery.
And in front of the anterior scalene is the subclavian vein. Now, the anterior triangle of the neck is what we're going to cover next. And its borders are as follows, the sternocleidomastoid and the mandible. and the anterior midline of the neck.
That's what makes our anterior triangle of the neck. And let's do it from the front. There's our sternocleidomastoid, our mandible, anterior midline. That's what makes the anterior triangle. And so there is mandible, anterior midline, sternocleidomastoid.
There is our anterior triangle of the neck. So the anterior triangle is subdivided into four triangles. So look at this picture and shing.
submandibular triangle, submental triangle, carotid triangle, and muscular triangle. Let's talk about the submandibular triangle first. We know this triangle because it's bordered by the anterior belly and the posterior belly of the digastricus muscle, as well as the mandible. We find that, those three borders, we find the submandibular triangle.
Let's zoom in and switch out the pictures. So there we now have one of the major contents that fills most of the space of the submandibular triangle is the... submandibular salivary gland. And then the facial artery is exiting deep from the gland and the facial vein is superficial to the gland.
And then any lymph nodes in this area are simply called submandibular lymph nodes. We remove the submandibular gland and you can see the facial artery and facial veins holding hands within this triangle. There is the, on the floor of the submandibular triangle is the myelohyoid muscle and tuck. right in back there is the hypoglossal nerve, cranial nerve 12 going to the tongue.
So let's zoom back out and now let's do the submental triangle. The submental triangle is bordered by the mandible, the anterior belly of the digastricus and our hyoid bone. And so we zoom in the major thing we see in there is submental lymph nodes.
The chin is the mental symphysis so below it is the submental triangle and the lymph nodes are submental lymph nodes. You may also see some tributaries of the anterior jugular veins. So let's now go to the carotid triangle and we have the borders of the posterior belly of the digastricus, the superior belly of the omohyoid, and the sternocleidomastoid.
That's what's making the carotid triangle. So if we then look at this lateral view and see, all right, here's a view and let's focus in on that triangular region. And so in there, the contents include our internal jugular vein, the carotid arteries, and our vagus nerve, which collectively are within the carotid sheath. If we recall, there's the carotid sheath and wrapped around the IJ are these deep cervical lymph nodes, draining much of the lymph from the head.
We also have the hypoglossal nerve, cranial nerve 12, that will eventually get into the submandibular triangle. And we also have the ansa cervicalis and other branches from the cervical plexus within this carotid triangle. Now, the carotid arteries is what I just put, but recall that the carotid arteries really come from the common carotid artery.
And whenever we see the prefix common with the vessel, we know it'll bifurcate. And we have one of those branches as the internal carotid artery, and its base is the carotid sinus and the carotid body, which are baro and chemoreceptors respectively. More on that in the vessels of the neck tutorial.
I should note also with In this carotid sheath, you're going to have the nerve to the carotid sinus and body, which is from cranial nerves 9 and 10. We also have all the branches off the external carotid artery that supply the face and a lot of the neck. All of those are branches that come off within this carotid triangle. Next, we're going to go into the muscular triangle, which is bordered by the omohyoid, the sternohyoid, and the sternocleidomastoid. And within there is primarily the side of the thyroid gland and parathyroid gland. And I didn't have any good pictures to show it.
And clinically, it's not that relevant, but it's in every single book. So I included it, but I don't care for my students if they ever know that triangle. So that, my friends, is showing all the triangles in the neck in a nutshell.