hey everyone ryan here and welcome back to our head and neck anatomy series this video will be about the anatomy of the temporomandibular joint so this joint is set apart from other joints in the human body for a couple of reasons the first is that it's a bilateral diaarthrosis which means that the left and right sides must function together it's impossible for the left tmj to be functioning while the right side is completely still and that's because they're both involving the mandible and as soon as you start moving it the other side is going to naturally respond this is true for protrusive movements lateral excursions as well as opening and closing movements the tmj is also one of only a select few joints in the body that are ganglimo arthrodial which means that they perform both hinge and sliding movement gingleamoid refers to hinging movement arthrodial refers to sliding movement the articulating surfaces of the joints are covered in fibrocartilage rather than hyaline cartilage which is the usual covering for joints in our body the tmj is an exception it has this more dense fibrocartilage that's able to withstand the constant pounding forces of mastication it's also the only joint in the human body to have a rigid endpoint of closure and that's where the teeth make occlusal contact the joint can no longer function and close anymore it's also the last joint to start developing and that begins at around seven weeks in utero all right so let's start with the articular disc this is made up of fibrocartilage again that dense fibrous connective tissue and it's devoid of any blood vessels or nerve fibers it's also mostly made of type 1 collagen it's a bi-concave shape which means that it's thinnest at its center and thickest at the edges like a red blood cell in fact it has variable thicknesses in its different regions the middle of course is thinnest because it's by concave that's also called the intermediate zone the anterior band is thicker than the middle but the posterior band is the thickest overall also medially the disc is slightly thicker than it is laterally the articular disc serves a bunch of functions one of which is to divide the joint into two separate compartments the upper joint space above the articular disc is responsible for translational movements like protrusion and retrusion the lower joint space below the disc is responsible for rotational movements like closing and opening the mouth the articular disc is sometimes also referred to as the meniscus behind the the articular disc are the retrodiscal tissues now highlighted in pink the alternative name for this is sometimes posterior attachment so the superior retrodiscal lamina or lamella is the upper layer of this tissue it's composed of elastic fibers that can stretch it attaches to the articular disc and it attaches it to the tympanic plate of the temporal bone its function is to counter the forward pull of the superior belly of the lateral pterygoid muscle on the articular disc so that lateral pterygoid muscle is going to put some pressure on that articular disc to move forward as the mandible is opened and so the disc and the condyle will move forward together this superior layer of retro-distal tissue is serving to prevent that disc from being dislocated anteriorly and it holds it back the inferior retrodiscal lamina down here has a similar function except it's composed of collagen fibers how i remember this is that inferior retrodiscal lamina is composed of in elastic fibers these collagen fibers that don't stretch as much it attaches the articular disc to the posterior surface of the condylar neck and it prevents excessive rotation of the articular disc over the condyle so similar but slightly different function and then of course we have the intermediate retrodiscal tissue in the middle of those two lamina and it consists of this loose ariel or connective tissue that's very vascular and innervated and it expands and fills with blood during jaw opening as the condyle moves forward the synovial membrane also called the synovium is composed of these specialized endothelial cells that line the inner surface of the joint capsule and secrete synovial fluid so both the superior joint space up here and the inferior joint space down here is aligned by this synovium and this fluid provides lubrication to minimize friction for the joint and it's also a medium for distribution of nutrients to provide metabolic requirements for the surrounding tissues the bones of the temporomandibular joint consist of the condyle of the mandible the mandibular or glenoid fossa of the temporal bone and the articular tubercle or eminence of the temporal bone so if we go back to this previous slide we have the condyle of the mandible the glenoid fossa or this depression and the articular eminence or tubercle just just ahead of that so the tmj is really an articulation between two bones the mandible and the temporal bone condyles may have several different normal shapes but the shape should be the same bilaterally so if you see someone with a convex condyle on one side and a flat condyle on the other well that could actually be one of the first signs of an arthritic change flattening of the condyle but if you have someone where both condyles are flat maybe that's just normal anatomy for that person the articular cartilage is composed of dense connective tissue once again fibrocartilage that lines the articular surfaces of the condyle and the mandibular fossa and again this is not hyaline cartilage which is usually the case for other mobile joints in the body because this fibrocartilage is stronger it's less susceptible to the effects of aging and has a much greater ability to repair it's made up of type 2 collagen rather than type 1 collagen that we saw in the fibrocartilage of the articular disc and it's composed of proteoglycans which are located within the connective tissue to provide shock absorption for withstanding compressive loading next we're going to talk about the ligaments of the joint these hold the skeleton together ligaments are always connecting two bones to each other they're made up of collagenous connective tissue that doesn't stretch and they act as passive restraining devices to limit and restrict joint movement they're all made up of primarily type 1 collagen so let's first start with the intrinsic or functional ligaments that are very close to that joint space and then we'll talk about the extrinsic or accessory ligaments that are a little bit further away the capsular ligament is a capsule that encompasses the entire joint space and it retains the synovial fluid it's well innervated and provides proprioceptive feedback the lateral ligament also called the temporomandibular ligament is composed of strong tight fibers that reinforce the integrity of the joint and attaches to the condyle from the articular tubercle this is a really important ligament that helps to keep the tmj intact the outer oblique portion which is this part right here resists excessive dropping of the condyle and therefore limits the extent of mouth opening the inner horizontal portion which is running up here prevents the disc and the condyle from dislocating posteriorly it also prevents the lateral pterygoid muscle from overextending so you can think of this ligament serving the opposite function of the superior retrodiscal lamina which was serving to prevent the disc from dislocating anteriorly next we have the collateral ligaments or the diskal ligaments and let's take a look at this picture first so now we're looking at a different view we're looking from a frontal view here so we have medial on the right and lateral on the left so these ligaments are these two tiny bands of tissue here and they attach the medial and lateral borders of the articular disc in gray to the medial and lateral poles of the condyle so i kind of think of it like a bucket handle on a bucket so you have the condyle as the main bucket and then the articular disc as the majority of this handle and then you have the two ligaments that are these two little connection pieces that hold the handle to the bucket and so that they're going to be always traveling together the condyle and the disc are going to be moving forward and back together as long as these ligaments are intact they also along with the articular disc divide the joint into superior joint cavity up here and an inferior joint cavity down here also i remember that the two ligaments that start with the letter c that's capsular and collateral are both of the ligaments that are innervated and vascularized so again strain on these ligaments is going to produce pain they're going to provide some sensation feedback so capsular and collateral are the two innervated ligaments all right now let's talk about the extrinsic or accessory ligaments the stylomandibular ligament is this one right here it's extending from the styloid process of the temporal bone to the medial angle of the mandible it's a thickening of fascia of the parotid gland and it limits excessive protrusion of the mandible so you can imagine that if the mandible was going this way this tight band of tissue is going to prevent the mandible from extending too far forward the spheno mandibular ligament extends from the spine of the sphenoid bone up here to the lingula of the mandible which is just above the mandibular foramen it's an embryonic remnant of meccal's cartilage and you can remember that meccal's cartilage is from arch 1 pharyngeal arch 1 and sphenomandibular ligament was also in that row for pharyngeal arch number 1. it helps to support the mandible but it actually has no limiting effects on its movement the targo mandibular riffey is not technically a temporomandibular joint ligament but i did want to include it here because this is a nice picture and it's this ligamentous band of tissue that extends from the pterygoid hamulus up here to the posterior end of this myelohyoid line and it connects to the buccinator in front and the superior pharyngeal constrictor in the back the last ligament i want to talk about is also not technically a tmj ligament but for comprehensiveness sake let's talk about it because it can pop up on the board exam this one is an embryonic remnant of rikert's cartilage which is from pharyngeal arch number two and stylohyoid ligament also appears in the row for frangial arch number two so that's that connection there it's also involved in eagle syndrome which sometimes come up comes up on board exams and this involves a symptomatic calcivide stylohyoid ligament that ligament is going to go from the styloid process to the hyoid bone and so if you have this symptomatic calcified ligament you can have sudden sharp pain in the mouth or even in the ear triggered by swallowing moving the jaw or turning the neck and it's more common in women between the ages of 40 and 60. the last thing i want to talk about is neurovascular supply to the joint and it's applied mainly by the auriculotemporal nerve of v3 it gets minor sensory contributions to the anterior region of the capsule from the masseteric and deep temporal branches also of v3 and as far as its vascular supply it's supplied mainly by the superficial temporal and maxillary arteries both branches of the external carotid artery which we'll talk about in the next video so how i remember the main ones is that they have this word temporal which of course is referring to the temporal bone of the temporomandibular joint so hopefully that can help you remember the two main suppliers to the tmj alright so that's it for this video thank you so much for watching everyone please like this video if you enjoyed it and subscribe to this channel for more on dentistry if you're interested in supporting the channel and what i do here please check out my patreon page thank you to all of my patrons here for all of their support you can unlock extras like access to my video slides to take notes on them and practice questions for the board exams so go check that out the link is in the description thanks again for watching everyone i'll see you in the next video