In this video, we're going to begin our introduction to joints. And so recall from our previous lesson videos that the human skeleton has over 200 bones, and almost all of them contact other skeletal elements at joints. Now, a joint is also known as an articulation or an arthrosis. And so when we say that one bone articulates with another bone, we just mean that those bones form a joint. And a joint, as its name implies, is going to join things together. And so a joint or an articulation or arthrosis can be defined as a contact point between 2 or more bones, or between a bone and tooth. And recall that teeth are technically not considered bone since they have a different composition. Now, it's helpful to note that the root arthro or arthro is a root that means joint. And we can see that root in the word arthrosis, as well as part of the root in the word articulation. And the word arthrology is a word that means the scientific study of joints.
Now, in addition to bones and teeth, joints can also contain a variety of other structures as well. Including different types of cartilage such as hyaline cartilage and fibrocartilage. Ligaments, which recall are dense connective tissues that connect bone to bone, tendons, which recall are dense connective tissues that connect bone to muscles, and muscles themselves. And so the presence and the roles of these particular structures can vary depending on the type of joint. And so different joints have different structures and functions, and essentially that dictates the roles and presence for each of these structures that are listed.
Now, it's important to note that joints actually serve 2 essential functions that we have numbered down below, number 1 and number 2. And so, the first essential function that joints serve is that they help to facilitate skeletal mobility or skeletal movement. And the second essential function of joints is that they help to provide structural stability. Now, it is important to note that there is a balance between skeletal mobility of a joint and structural stability of a joint. And so these 2 are inversely related to one another. Which means that the greater the range of motion a joint has, the less stable that joint will be. And the less motion that a joint has, the more stable the joint will be.
And so for example, the joints that connect our bone to our teeth keep our teeth pretty still or stationary. And so our teeth don't really move around a whole lot. And so because they have less motion, that means that they are more stable. Whereas our shoulder joint that connects our humerus to our scapula, for example, has a lot of motion. And because it has a lot of motion, it is less stable. And because it's less stable, it's more prone to injuries.
And so, let's take a look at our image down below where we can see a few examples of these joints. And so, notice on the far left we're focusing in on this human skeleton on these specific regions. The first region is the hand, and so we're showing you a zoom in here of finger joints. And so notice here is the hand which has a variety of different bones and up above we're zooming in on the finger joints. And so notice that the finger has a variety of bones that you can see highlighted here and the contact point between these bones, which are circled here, are the joints.
Now, we're also focusing in on the shoulder joint, which you can see over here. The shoulder joint is going to connect the humerus, this long bone of the upper arm, to the scapula, which is our shoulder bone. And, notice that involved in this joint is some cartilage, which you can see here. And, we're also showing you some muscles and some tendons, and there are also ligaments involved in this joint as well.
Now, over on the far right we're also focusing in on the teeth. And so, the bone to teeth or tooth connection is also considered a joint. And so notice here we're zooming in to the tooth, and notice the tooth is being connected to the jaw bone, which you can see underneath here, and that is considered a joint. And recall that teeth are technically not considered bones because again, they have a different composition. And moving forward in our course we're going to talk a lot more about joints, including their structures and functions. But for now, this here concludes our brief introduction to joints, and so I'll see you all in our next video.