If you didn't have any joints, you wouldn't be able bend down to tie your shoes or throw a ball. Joints are found where the bones of your skeleton meet. Learn about the different types of joints and how they differ in how much they let you move.
Inside of you, there are 206 bones that make up your skeleton. These bones act like the frame of a house, allowing you to stand tall. Without them, you would collapse in a heap of soft tissues and have to slither along the ground like a worm. You are able to bend your bony skeleton thanks to joints, which are the areas where bones connect. Without them, you would be able to stand, but you would have to waddle around stiff-legged to get anywhere. Every bone in your body is connected to another bone by a joint, except for one lonely bone found in your neck. I'll tell you the name of that bone and what it does, but you'll have to wait till the end of the lesson.
Your joints differ in the amount of movement they allow. In fact, there are some joints that don't move at all. A perfect example is the immovable joints that hold the individual bones of your skull together. Inside your head, these bones are fused tightly together to protect your brain from getting hurt. But, when you were first born, these joints were not fused; this allowed the bones to flex during birth and made room for your big brain to grow. Did you ever feel the soft spot on a baby's head? At the top of babies' heads is an area that feels soft to the touch. This is part of a joint that has not yet fused, and while it might seem like a place prone to injury, it's actually made of a fairly tough fibrous tissue.
Slightly Movable Joints
You have other joints that allow partial movement called slightly movable joints. A great example is the joints of your spine. The individual bones of your spine, called vertebrae, are connected, and they move in relation to one another, kind of like the cars on a moving train. When you bend over to tie your shoes or twist at your waist, each vertebrae in your back moves a little bit allowing for an overall big movement.
Freely Movable Joints
You also have joints that allow a lot of movement called freely moveable joints. These joints are found mostly in your limbs, which makes sense because movement is really important in these areas of you. Freely movable joints contain synovial fluid, which is a fluid that acts as a lubricant. In fact, this fluid is so important that any joint with this fluid, including a few in your spine, is referred to as a synovial joint. The lubricating fluid helps keep your joints healthy and reduces friction when you are doing repetitive things like pitching nine innings of a baseball game or running long distances.
You have three types of freely movable joints. The ball and socket joints of your shoulders and hips are the most freely movable. The two bones that make up these joints have a funny shape; one is rounded, like a ball and the other is cupped like a baseball glove, or socket. This unique connection allows you to move your shoulder and hip up, down, around and in all kinds of directions.
Another type of freely movable joint is the hinge joints. These only move in one direction, just like the hinge on a door. Can you guess where they are located? If you guessed your elbows and knees, you are correct.
Now, you might notice your lower arm is able to twist. This is not a movement of your elbow joint, but rather this movement is created by the third type of freely movable joint known as pivot joints. Pivot joints allow the rotation of one bone around the other, which is what happens as one bone of your forearm rotates around the other. This type of joint is also found at the top of your neck where the first two vertebrae meet. Thanks to this joint, you can say no, just by swiveling your head from side to side.
And, one last thing - at the start of this lesson I told you there was one bone that is not connected to any other; that bone is called the hyoid bone, and it's found floating in the front of your neck, near the top of your throat. You might be able to feel it in there if you gently touch this area. It's shaped like a 'V,' and while it doesn't connect to another bone, it does connect to your tongue, which gives your tongue a wide range of movement.
Let's review. Joints are the areas where bones connect. Your joints differ in the amount of movement they allow. Immovable joints are joints that don't move at all, like the ones that hold your skull bones together. Slightly movable joints are joints that allow partial movement. You can find some of these in the spine because they join the vertebrae together. Freely moveable joints are joints that allow a lot of movement. These joints are found mostly in your limbs and contain synovial fluid, which is a fluid that acts as a lubricant. Because of this, they are also referred to as synovial joints.
You have three types of freely movable joints:
- The ball and socket joints of the shoulders and hips are the most freely movable.
- Another type is the hinge joints of the elbows and knees that only move in one direction.
- Lastly, we have the pivot joints of the forearm and upper neck that allow the rotation of one bone around the other.
Absorption of this lesson's material could enable you to:
- State the purpose of joints
- Characterize immovable joints and slightly movable joints
- List the three types of freely moveable joints
- Understand the purpose of synovial fluid