Introduction to Joints - Online Tutor, Practice Problems & Exam Prep

Joints, or articulations, are contact points between two or more bones, facilitating skeletal mobility and providing structural stability. They can be classified into functional categories: synarthroses (immovable), amphiarthroses (slightly movable), and diarthroses (freely movable). Structurally, joints include fibrous, cartilaginous, and synovial types. The balance between mobility and stability is crucial; for instance, the shoulder joint allows extensive movement but is less stable, while teeth joints are stable due to limited motion. Understanding these classifications aids in comprehending joint functions and their roles in the skeletal system.

Introduction to Joints

In this video, we're going to begin our introduction to joints. 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 arthrosis. When we say that one bone articulates with another bone, we just mean that those bones form a joint. A joint, as its name implies, joins things together.

A joint or an articulation or arthrosis can be defined as a contact point between 2 or more bones, or between a bone and a tooth. Recall that teeth are technically not considered bones since they have a different composition. It's helpful to note that the root 'arthro' or 'arthro' is a root that means joint. We can see that root in the word 'arthrosis' as well as part of the root in the word 'articulation.' The word 'arthrology' means the scientific study of joints.

In addition to bones and teeth, joints can also contain various other structures, including different types of cartilage such as hyaline cartilage and fibrocartilage. Ligaments, dense connective tissues that connect bone to bone. Tendons, dense connective tissues that connect bone to muscles, and muscles themselves. The presence and roles of these particular structures can vary depending on the type of joint.

Different joints have different structures and functions, which essentially dictate the roles and presence for each listed structure. It's important to note that joints serve two essential functions. The first essential function that joints serve is that they help to facilitate skeletal mobility or skeletal movement. The second essential function of joints is that they help to provide structural stability. There is a balance between skeletal mobility and structural stability in a joint.

These two are inversely related to one another, meaning 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. For example, the joints that connect our bone to our teeth keep our teeth relatively still or stationary. Because they have less motion, that means they are more stable. Whereas our shoulder joint that connects our humerus to our scapula has a lot of motion. Because it has a lot of motion, it is less stable and more prone to injuries.

Let's take a look at our image down below, where we can see a few examples of these joints. Notice on the far left, we're focusing on this human skeleton on these specific regions. The first region is the hand, and we're showing you a zoom-in here of finger joints. The hand has a variety of different bones, and above, we're zooming in on the finger joints. Notice that the fingers have a variety of bones that you can see highlighted here, and the contact points between these bones, which are circled here, are the joints. We're also focusing on the shoulder joint, which you can see over here.

The shoulder joint connects the humerus, this long bone of the upper arm, to the scapula, our shoulder bone. Notice that involved in this joint is some cartilage, which you can see here. We're also showing you some muscles and tendons, and there are also ligaments involved in this joint. Over on the far right, we're also focusing on the teeth. The bone-to-teeth or tooth connection is also considered a joint.

Notice here we're zooming into the tooth and notice the tooth is being connected to the jawbone, which you can see underneath here, and that is considered a joint. Recall that teeth are technically not considered bones because they have a different composition. 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 I'll see you all in our next video.

Introduction to Joints Example 1

So, here we have an example problem that wants us to rank the following joints in order from the least range of motion, which we'll label as number 1, to the greatest range of motion, which we'll label as number 4. And then it wants us to predict how this would affect their ability to provide structural stability and support. Notice that the four joints we're showing you here in this example are the shoulder joint, which is found in our shoulder connecting the humerus to the scapula. The sutures of the skull are also a joint, and those sutures are essentially the cracks that you can see in the skull highlighted there. We also have the intervertebral joints, which are found in our spine in our back.

Lastly, we have the knee joint, which is found in our knee. In terms of the range of motion, we can go through each of these one by one. Our shoulder joint allows for quite a lot of movement. Our spine allows us to lean forward and lean backward, which also permits some movement. Our knee joint allows for movement of our knee.

However, what you'll notice is that the sutures of the skull, the cracks essentially that you can see here highlighted in the skull, are not very mobile. They do not have a great range of motion; they have very low range of motion. For that reason, they have the least range of motion of all the joints here, and we can label the sutures of the skull as number 1. Our spine does allow for some motion; we're able to lean forward and lean back. However, the range of motion of our spine is limited and does not allow for as great of a range of motion as the knee or the shoulder. Thus, the intervertebral joint is going to be number 2 in terms of the order or the ranking of the range of motion. The knee has less range of motion than the shoulder, so we can label the knee joint as number 3, and the shoulder joint has the greatest range of motion of all these joints, and we'll label it as number 4.

Now that we've ranked these four joints in terms of their range of motion, let's focus on their ability to provide structural stability and support. Recall from our last lesson video that there is an inverse relationship between the skeletal mobility of a joint and the structural stability of a joint. The greater one is, the less the other is. The greater the range of motion a joint has, the less stable that joint is. The shoulder joint here has the greatest range of motion of these four joints.

Because it has the greatest range of motion, it also is the least stable. That makes it more prone to injuries such as dislocations, for example. The sutures of the skull, the cracks that you can see here in the skull, are going to have the least range of motion among these four joints. Because it has the least range of motion, it has the greatest structural stability among these four joints. That's going to be very important for the skull to have great structural stability because the skull plays a critical role in protecting our brain.

Of course, we want to prioritize structural stability and support when it comes to the skull and protecting our brain. This here concludes our example problem, and we'll be able to get some practice applying these concepts and learn a lot more about joints as we move forward. So, I'll see you all in our next video.

Why is dislocation of the shoulder joint one of the most common joint injuries?

• A. Most sports put a lot of stress on the shoulder joint.
• B. People often try to lift things that are too heavy.
• C. It has a very large range of motion, meaning it's relatively unstable.
• D. It's designed to dislocate to allow us to have a greater range of motion.

Map of the Lesson on Joints

In this video, we're going to introduce our map of the lesson on joints, which is down below right here. And because this is a map of our lesson, it is essentially a table of contents that you can continuously use to help guide you through our lessons on joints. Now, as we move forward in the lesson, we will also double click to expand and compress portions of the map in order to make this map even more relevant to you as we move forward. Now, the way that we're going to follow this map is from a top to bottom approach, but also from a left to right approach. And so, notice at the very top of the map we have the introduction to joints, which is where we currently are in the lesson.

And moving forward, we are going to cover the functional classes of joints. And as you can see here in this map, there are 3 functional classes of joints. And they are the synarthroses, the amphiarthroses, and the diarthroses. Now, one thing to keep in mind here is that moving forward in our lesson, we are going to use these symbols to represent each of these functional classes. And so, as we'll learn moving forward in our course, the functional classes of joints are categorized based on the amount of movement or the amount of mobility that the joint allows for.

And so, synarthroses are actually immovable joints that do not allow for any movement. And because that's the case, notice that the symbol does not have any movement arrows going around it. Now, the amphiarthroses, as we'll learn moving forward in our course, actually allow for a little movement. And because that's the case, notice that the symbol we use has one movement arrow going around it to remind us that amphiarthroses have a little movement. Now, the diarthroses, as we'll learn moving forward in our course, allow for dynamic or free or large range of movement.

And because that's the case, notice the symbol that we use has multiple movement arrows going around it to represent that dynamic movement of these diarthroses. And so, once again, moving forward in our course, we will utilize these symbols to represent each of these functional classes. Now, what you'll notice is moving forward in our course, we will then cover the structural classes of joints. And notice that there are also 3 structural classes of joints, which are the fibrous joints, the cartilaginous joints, and the synovial joints. And so, notice that there are multiple fibrous joints that include sutures, gomphoses, and syndesmoses.

And what you'll notice is that the sutures are going to be categorized as synarthroses because it has the red s symbol around it. And so, what this means is that the sutures are immovable joints that don't allow for any movement, as we'll learn moving forward in our course. And the same applies for the gomphoses. The gomphoses are a type of fibrous joint that is also categorized as synarthroses because again, it has that red s symbol around it. However, notice that the syndesmoses have the blue a around it, and so it is categorized as amphiarthroses.

Meaning, it allows for a little movement, as we'll learn moving forward in our course. Now, when it comes to the cartilaginous joints, there are 2 types and they are the synchondroses and the symphysis. Now, the synchondroses are categorized as synarthroses because again, it has that red s around it. Meaning that it is going to be an immovable joint that does not allow for any movement. And then the symphyses have the blue a around it, which means that they are categorized as amphiarthroses, meaning that they allow for a little movement.

And so you can see how the functional classes of joints overlap with the structural classes of joints in that fashion. Now, when it comes to the synovial joints, it turns out that they are all categorized as diarthroses, meaning that they allow for dynamic or a wide range of movement. And so what you'll notice is that we've got different types of synovial joints listed here, including plane joints, hinge joints, pivot joints, condylar joints, saddle joints, ball and socket joints. And notice that all of them have this symbol here that represents the diarthroses. And so, moving forward in our course, we'll be able to again utilize these symbols for synarthroses, amphiarthroses, and diarthroses, and we'll be able to learn a lot more about each of these different types of joints.

And so this here concludes our brief lesson on the map of the lesson on joints, and I'll see you all in our next video.

Which of the following is a correct description of syndesmoses?

• A. Fibrous synarthrosis.
• B. Cartilaginous amphiarthrosis.
• C. Fibrous amphiarthrosis.
• D. Fibrous diarthrosis.

Here’s what students ask on this topic:

What are the main functions of joints in the human body?

Joints, or articulations, serve two essential functions in the human body. First, they facilitate skeletal mobility, allowing for a range of movements such as bending, twisting, and rotating. This is crucial for performing everyday activities and complex motions. Second, joints provide structural stability, ensuring that the skeleton maintains its integrity and supports the body's weight. The balance between mobility and stability is important; for example, the shoulder joint allows extensive movement but is less stable, making it more prone to injuries. In contrast, the joints connecting teeth to the jawbone are highly stable but allow minimal movement.

How are joints classified functionally and structurally?

Joints are classified both functionally and structurally. Functionally, they are categorized based on their range of movement: synarthroses (immovable), amphiarthroses (slightly movable), and diarthroses (freely movable). Structurally, joints are divided into three types: fibrous, cartilaginous, and synovial. Fibrous joints include sutures and gomphoses, which are typically immovable, and syndesmoses, which allow slight movement. Cartilaginous joints include synchondroses (immovable) and symphyses (slightly movable). Synovial joints, such as hinge and ball-and-socket joints, are all freely movable and allow for a wide range of dynamic movements.

What is the difference between synarthroses, amphiarthroses, and diarthroses?

Synarthroses, amphiarthroses, and diarthroses are functional classifications of joints based on their mobility. Synarthroses are immovable joints, such as the sutures in the skull, which provide stability. Amphiarthroses are slightly movable joints, like the symphysis pubis, allowing limited movement while maintaining stability. Diarthroses are freely movable joints, such as the shoulder and hip joints, which permit a wide range of movements but are less stable and more prone to injuries. Understanding these classifications helps in comprehending how different joints contribute to both movement and stability in the skeletal system.

What are the different types of synovial joints and their functions?

Synovial joints are classified into several types based on their shapes and the movements they allow. These include plane joints (allowing gliding movements, e.g., intercarpal joints), hinge joints (allowing flexion and extension, e.g., elbow), pivot joints (allowing rotational movement, e.g., atlantoaxial joint), condylar joints (allowing movement in two planes, e.g., wrist), saddle joints (allowing movement in two planes with greater freedom, e.g., thumb), and ball-and-socket joints (allowing the most extensive range of movement, e.g., shoulder and hip). Each type of synovial joint is specialized to facilitate specific types of movements, contributing to the overall flexibility and functionality of the skeletal system.

Why are shoulder joints more prone to injuries compared to other joints?

The shoulder joint, a type of ball-and-socket joint, is more prone to injuries due to its extensive range of motion. This joint allows for dynamic movements in multiple directions, making it less stable compared to joints with limited mobility. The trade-off between mobility and stability means that while the shoulder can perform complex movements, it is also more susceptible to dislocations, strains, and other injuries. The surrounding muscles, tendons, and ligaments provide some stability, but the high degree of movement increases the risk of injury, especially during activities that involve heavy lifting or sudden, forceful motions.