hello everybody and welcome back today we're going to be looking at the cranial vertebral joints as well as the ligaments and muscles that support these joints essentially what we're looking at is the interaction between the occipital bone and C1 the atlas as well as the interaction of C1 and C2 the atlas and the axis bones and it's these unique combination of bones that allow for a lot of movement to occur in a very vulnerable area of anatomy and I want to use a CT scan to show you these bones as well as the ligaments and muscles so let's go to the axial CT scan of the neck and we're going to scroll superiorly into the cranium we've looked at the cranium now in multiple previous talks we know that this posterior bone here is the occipital bone and it's flanked by the temporal Bones the occipital bone at its inferior border has this large opening known as the Fram and Magnum now lateral to the Fram and Magnum is the lateral parts of the exal bone and anterior to the frame and Magnum is the basil part of the oxal bone that becomes the clus ascending super superiorly towards the sphenoid bone now the occipital bone if we scroll down inferiorly we will see these two projections remaining here these are what's known as the occipital condal they're the articular surface that articulates with C1 or the atlas let's have a look at what that looks like on our sagittal image here we can see the clus ascending towards the sphenoid bone this point Here is known as the bason we've got the aiston posteriorly this opening here is the veran Magnum as we scroll out out laterally then we will see the occipital conds here which are going to articulate with C1 or the atlas on the coronal scan you can see that these occipital Condes have a very unique look and this is what often gets people confused they confuse the occipital Condes here laterally as being C1 they kind of look like vertebrae in themselves you can see how this may have been a vertebrae back in evolution that is now fused with the bottom of the skull here so here are occipital conds laterally let's scroll anteriorly and see how that becomes the cus here here's Al basion and as we head out posteriorly the veran Magnum being formed as we head out more and more posteriorly we're going to get to the squamous part of the occipital bone here so we're scrolling through the frame and Magnum and we can see how those inferior projections here what's known as the occipital conds now as we scroll through the occipital condal we've looked at this before and I want to show you it again we have this canal that runs from medial to lateral medial to lateral heading out of the cranium that's what's known as the hypoglossal canal where the hypoglossal nerve cranial nerve 12 travels through now this is a very good Landmark to find when you're looking at the coronal scan because we get what looks like an eagle facing outwards and its beak wrapping over the hypoglossal canal that shows us that this is the occipital condal above this part of Bing here is what's known as the jugular tuberal below is our occipital condal and that's the hypog Canal this joint here then is between the occipital condal and the atlas now the atlas in Greek mythology is the man who is condemned to eternally hold up the sky or the heavens the same thing is happening here the atlas is holding up the cranium this joint is what's known as the atlanto occipital joint the superior articular process of the atlas articulates with those occipital condal now this joint predominantly allows for extension and flexion of the cranium you can see on our lateral view here how there's this small divot posteriorly that's what's known as the condop fosa it allows for these articular processes of the atlas bone here this posterior margin to be accommodated for when we get extreme extension in the neck it allows for this Cranium to go all the way back and this articular process to glide into this cond fosa so we got predominantly flexion and extension there's a slight lateral flexion that can happen at this joint here but it's limited by the lateral margins or the lateral part of the aital bone you can see that better on our 3D model the predominant movement here is anterior and posterior flexion and extension so let's go and have a look at the atlas bone now now the atlas bone is unique our vertebra as we commonly know them have an anterior vertebral body then they have a pedicle that attaches the vertebral body to the transverse processes and those transverse processes are attached to the posterior spine by the Lamela now there is no anterior body in the atlas in C1 here you can see instead we have an anterior Arch and a posterior Arch that is connected by these lateral masses here posterior to this anterior Arch we have a bony protrusion coming up from C2 known as the odontoid peg or the odontoid process or just the peg we're going to look at that more specifically when we look at C2 on the anterior surface here it's not very pronounced on this patient we have what's known as an anterior tubercle and posterity we've got posterior tobal these are going to be attachment points for muscles and ligaments that we're going to look at later on now because we don't have a vertebral body we don't have pedicles extending out towards the transverse processes we can see our transverse processes here and we can see the transverse forment of which the vertebral artery is going to travel up and C1 actually has transverse fora that face slightly laterally and posteriorly and when we look at the vertebral artery in a later talk we're going to see the different parts of the vertebral artery and how as it travels through the trans parameter of C1 that vertebral artery juts out laterally extends out posteriorly before heading into the frame and Magnum now we don't have pedicles what do we have when we look at C1 if we look at our coronal view here you can see that between the articular surface here at the atlanto occipital joint and the articular surface inferiorly between the atlanto axial joint we've got this chunk of tissue here this is what's known as the lateral Mass the bone between these two articular surfaces is what's known as a pause into articularis the pause the piece into between articularis between the articulating surfaces and this is an important part of the bone to remember it's often forgotten about especially when we're looking at it on these axial slices here now as we scroll more inferiorly we're going to come into contact with C2 C2 is also known as the axis when we think about the word axis we know that that's a point for rotation to occur Atlas holding up the cranium ACC this allowing for rotation the predominant movement here is rotation of the head now when we're talking about flexion and extension or rotation it's not just these joints that are contributing to that movement our whole cervical spine is going to be moving so let's have a look at C2 there's a couple of differences in C2 firstly we talked about this Superior projection of bone known as the DSE or the odontoid process you can see how that perhaps used to be the body of C1 before we started needing to look over our shoulder and look for now if we look on our axial plane and we scroll upwards we can see the dense now articulating with this anterior Arch this is the first joint we're going to look at between the atlas and the axis this is what's known as the median atlanto axial joint median because it's occurring in the middle here and atlanto axial because it's occurring between the atlas and the axis now there's a median atlanto axial joint obviously there's going to be lateral atlanto axial joints this is best viewed on alaron plane and we can see the lateral atlanto axial joints forming here notice the orientation of these joints they are going from Superior to inferior and those joints are facing out laterally now that's in contrast to our atlanto occipital joints which are going from Superior to inferior and facing out medially we've got this wedge here being formed by the atlas now if we were to apply an axial load here where we were to apply a lot of weight down onto the cervical spine you can see what would happen to C1 here because of the orientation of these joints the C1 lateral masses are going to protrude out laterally if we have an axial load that causes what's known as a jeffersin fracture these lateral masses here extend out laterally and we get a fracture in both the anterior and posterior arches here so we're at the level of C1 let's scroll inferiority to the level of C2 and we can see that C2 has more of a vertebral body forming here you can kind of see that on our 3D model we know that as we extend down inferiorly on our spine the vertebral bodies get bigger and bigger so the C2 vertebrae has the small vertebral body laterally it's got transverse processes with an anterior and a posterior tubercle and we can see our transverse Forman where the vertebral artery is going to extend out here's where the vertebral artery really extends out laterally it had Arisen in a very vertical manner through the cervical spine as it reaches C2 that vertebral artery juts out laterally before going up through C1 we can see that there are Lamela on either side heading out towards the spinus process and C2 prominantly has a biffer spinus process there's two spinus processes here as we head down more and more inferiorly you can see how those spinous processes become one single spinus process let's head down further into say the thoracic spine here and I just want to show you a pedicle here see how the vertebral body has a pedicle extending out to the transverse processes there's no transverse foramina here because we've got no vertebral artery traveling through and the spine is processed posteriorly Okay so we've looked at the Bony components now of the occipital Condes C1 and C2 the atlas and the axis now there's a lot of movement happening here but we don't want these bones to shift over one another we want those bones to be stabilized because we've got the spinal cord running through the vertebral Canal here now there are multiple ligaments that stabilize this joint and I want to touch on the most important ligaments in these cranial vertebral joints the first ligament we're going to look at is between the dense and the atlas here running posterior to the dense is a ligament that goes from one medial border of the atlas to another medial border of the atlas here wrapping around the back of the dance this is what's known as the transverse ligament of the atlas it keeps this median atlanto axial joint in place it prevents the C1 from slipping forward over C2 we also have a ligament that extends from the dense and attaches to the occipital bone it extends superiorly and slightly laterally and that's what's known as the AAR ligaments as we head up superiorly we can see the occipital Condes coming into view here between the tip of the D and the occipital condil is a ligament traveling here known as the AAR ligaments let's have a look at our coronal scan we can see how the den comes into close contact here with the occipital condal and with the basion of the occipital bone the AAR ligaments travel obliquely like this we also have an apical ligament that travels from the superior border of the dence vertically upward superiorly to the bason here that's what's known as the apical ligament so the den has a transverse ligament of the atlas wrapped behind it it's got AAR ligaments extending out towards the occipital bone and it's got an apical ligament traveling superiorly to the occipital bone or to the bason when we look at our sagittal plane here we know some of the common ligaments of the spinal column we've got the anterior longitudinal ligament a ligament that runs up this anterior border we've got a posterior longitudinal ligament that runs along the posterior border of the vertebral bodies and we have a ligament on the posterior part of the vertebral Canal known as the ligamentum flavor now why am I mentioning these ligaments well ligaments connect bone to bone remember tendons muscle to Bone ligaments bone to bone and they don't allow for much movement think about the ligaments in the knee we don't want that knee joint to be able to separate those ligaments make a strong connection at the cranial vertebral joints there's a lot of movement happening we can't afford to have extremely strong ligaments that don't allow for movement now what happens is as those ligaments extend the anterior longitudinal ligament the posterior longitudinal ligament and the ligamentum flavor as they extend superiorly they start to become membranes those membranes allow for a little bit more movement but they actually extensions of those ligaments and it's those membranes that are going to encapsulate these joints between the SE C1 and C2 and between C1 and the oxit now between the anterior surface of C2 of the axis and our Atlas the anterior surface of C1 we get what's known as the anterior atlanto axial membrane that then extends superiorly here and we get a membrane forming between C1 and the oxit that's what's known as the anterior atlanto occipital membrane now we've talked about the apical ligament here posteriorly we've got the posterior longitudinal ligament that wraps over the transverse ligament of the atlas remember when we looked at our axial scan here and we looked at the dense we said posterior to the dense there's this transverse ligament of the atlas that transverse ligament of the atlas then lies underneath the posterior longitudinal ligament that then becomes a membrane and attaches to the internal surface of the bason here to the front part of the framan Magnum those membranes allow for a lot of movement here now the ligament and Flav them as well also becomes a membrane as it heads up superiorly becomes the posterior atlanto axial membrane and the posterior atlanto occipital membrane that membrane is a broad membrane that makes a capsule between C1 and C2 and C1 in the ocopus now there's small openings laterally of that membrane to allow for the vertebral artery to head into the frame and Magnum we can see how that vertebral artery goes into the frame and Magnum using our 3D model here now those are the major ligaments and membranes that I want to touch on now now want to look at some of the muscles that surround the Deep parts of the cical spine now we're going to talk about the muscles of the neck extensively in another video the muscles I want to talk about today are the Deep muscles of the cervical spine that lie right next to the regions that we've been looking at we're going to look at the prevertebral anterior muscles and we're going to look at these suboccipital muscles posteriorly we're not going to be talking about the trapezius and the sternic and mastoid we're going to look at those later on now a common question in anatomy exams is to ask you to label some of these muscles and if you look at the slice here there's a whole load of muscles moving everywhere and it's quite difficult to tell let's look at the preverbal muscles that run anterior to the cervical spine now remember the anterior neck has a lot of space where muscles can't run we've got the oral cavity we've got the fank there's very little space you can see on the sagittal here for muscles to run along the anterior surface of the cical spine there's not much leverage there you can also see that the cranium most of its weight lies anteriorly if all of these muscles lost their tone the cranium would tip anteriorly it's the posterior muscles that allow us to have that tone that allow us to keep the head upright like this these anterior muscles as a result lie very close to the anterior surfaces of the bones that we've been looking at now in terms of prevertebral muscles we've got two sets of muscles we're going to look at today the longest capitus muscles and the longest COI muscles they both run up these anterior surfaces we're at the level of C1 and we can see two muscles lying anteriorly left and right the these muscles extend superly and attach to the base of the occipital bone this is what's known as the longest capitus muscles they reach the cranium they reach the head hence the name capitus those longest capitus muscles as we head down inferiorly we're going to see they fan out slightly laterally and they start attaching to the transverse processes of C3 to C6 so those longest capitus muscles run from the transverse processes head medially and then extend up and attach to the base of the occipital bone now why am I going into a lot of detail like this well the longest Coy muscles they don't extend past the atlas they attach to this inferior border inferior anterior border of the atlas and they head down inferiorly as we scroll down inferiorly we can see these small slips of muscles anterior to the vertebral bodies here this is what's known as the longest COI muscles now because they don't extend past the atlas whenever you ask in an anatomy exam what these muscles are here and we can see that we're above the level of the atlas we know that these can't be longest corly anymore they must be longest capitus as we extend down infer we can see that the medial muscles lying closest to the vertebral bodies are going to be the longest COI muscles and those laterally and slightly anterior are going to be the longest citus muscles these are the kind of questions that you get asked in anatomy exams and they're the kind of questions that I've tried to ask in the anatomy question bank that I've linked below they assume that you know which level that you're at and they assume that you know the intricate relationship between between these two muscles now anteriorly there are two other muscles that I still want to look at and these muscles connect the atlas to the occipital bone itself so on this Superior surface of the anterior arch of the atlas here we have a small muscle that runs between the anterior Arch and the occipital bone it's best viewed on our coronal plane as we head out anteriorly here you can see this muscle running between the anterior arch of the atlas and the occipital bone this is what's known as a rectus capitus anterior the rectus capus anterior runs in a vertical line like this if we still remain on the coronal plane but head out posteriorly slightly so that we can see the transverse processes of C1 we can see another muscle here known as the rectus capitus lateralis so we've got these two rectus capitus muscles that attach this Atlas to the occipital bone very small muscles there so these muscles are anterior muscles they come from the anterior border both prevertebral and the anterior border of C1 now I want to look at some of of the posterior muscles and only the suboccipital posterior muscles we can separate sub occipital muscles into rectus capitus muscles and oblas capitus muscles now the rectus capitus posterior muscles make a vshape behind the cervical vertebrae the rectus capitus major runs from the spinus process of C2 all the way to the oxit so let's find the spinus process of C2 we know that's the biffed process here as we head up superiorly we should see a large muscle running from that spinus process all the way up to the oxit here that's the rectus capitus major you may have noticed that as we were scrolling there was a small muscle underneath the rectus capitus major that's what's known as the rectus capitus minor if we have a look on the coronal scan and scroll out posteriorly we'll be able to see that rectus capitus major nicely outlined here above the rectus capitus major running from the posterior arch of C1 there's the rectus capitus minor here you can see that small muscle from the posterior aspect of C1 also heading up towards the oxit here rectus capus major and minor now there are two other muscles that I want to look at the obliquus capitus muscles now the oblas capitus muscles one of them heads up to the skull one of them doesn't actually reach the head it's still called capitus but it doesn't reach the head the one that doesn't reach the head runs from the spinus process of C2 and extends out to the transverse processes of C1 it connects C2 to C1 that's what's known as the oblas capitus inferior so as we scroll up soon period we'll be able to see this muscle here you see the transverse process of C1 there's a muscle belly here that then runs all the way back down to the spinus process of C2 that's the obliquus capitus inferior the oblas caus superior runs from the transverse process of C1 up to the oxop it now these are called oblas muscles because they don't run vertically like our rectus citus muscles did if we look at our 3D model you can see how obliquely these muscles need to run in order to connect the structures that we're talking about from the spinus process of C2 to the transverse process of C1 is a very oblique angle the same as from the transverse process of C1 backwards towards the nucal lines of the oxit so let's have a look at the oblas capitus superior we find the transverse process of C1 might be better actually to look at it on our coronal scan find the transverse process of C1 and then we know that we need to head out post poly we should see here's a muscle Betty heading out posteriorly and attaching to the oxit here we can see that again on our axial slice as we head up superiorly from the transverse process we should see a muscle belly running out posteriorly here and attaching to the oxit that is running a very oblique CLA as it heads out posteriorly now there's so much Anatomy to cover here and these bones aren't regularly shaped and the ligaments run in strange courses as well as the muscles so I'd encourage you to spend some time going through this video but also looking at other Anatomy resources and try and consolidate this knowledge it's a very complicated area and an area that people love to ask about in exams if you know this Anatomy well it's a good indication that you've gone through your anatomy in great depth when you're preparing for that Anatomy exam so in our next talk we're going to be looking at the rest of the cical spine in nowhere near as much detail as we' looked at in this talk because the rest of the survical spine is pretty standard actually so I'll see you all in that talk goodbye everybody