Joints: Structure and Functions

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  • 0:05 What Makes Movement Possible
  • 0:28 The Joint and Joint Capsule
  • 1:11 The Synovial Membrane
  • 1:54 Bursa
  • 2:15 The Meniscus
  • 2:54 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem is a doctor of veterinary medicine and has taught science and medicine at the college level.

Find out what part of your body is affected when you tear your meniscus, how synovial fluid is made, what the synovial membrane helps to comprise, what a joint is, and why a joint capsule is important.

What Makes Movement Possible

We are well aware that the skeleton is responsible for supporting and protecting our body. However, if all of the bones of the skeleton were fused together, we wouldn't be able to do anything! We, literally, wouldn't be able to move. Thankfully, our body has certain structures that allow for movement despite the relative rigidity of bone itself.

The Joint and Joint Capsule

Synovial joints have joint capsules, which are sacs that enclose the joint cavity.
Joint Capsule

These structures, which allow for motion, are called joints and are places where two or more bones come together in order to allow for the movement and support of our body.

The most common type of joint in your body, called a synovial joint, has what's known as a joint capsule, which is a sac composed of the fibrous and synovial membranes that surround a joint in order to enclose a space, called a joint cavity.

The joint cavity within the joint is filled with a protective fluid called synovial fluid. If there was no joint capsule, the joint space would have nothing with which to hold in the protective synovial fluid.

The Synovial Membrane

Without synovial fluid, the cartilage at the end of each bone would wear away due to friction.
Joint Friction

This synovial fluid in the joint cavity is formed by the synovial membrane, which is a thin membrane that combines with the fibrous membrane to form the joint capsule. This synovial fluid looks a bit like egg whites, which helps explain why the word 'ovum,' or egg, helps to make up the word syn-ovium.

If you were wondering, this fluid functions to provide lubrication for the movement of the bones that make up a joint. If there was no synovial fluid, the cartilage at the end of each bone would wear away very quickly due to quite a bit of friction, and this would eventually cause you a lot of pain.


For added protection, many joints have something called a bursa, which is a synovial fluid-filled sac that helps to reduce the friction between a bone and a muscle or a bone and a tendon. Basically, the bursa is like a fluid-filled pillow. It cushions the impact between the two structures that surround it.

The Meniscus

Another form of added protection in some joints, namely the knee joint, is a structure called a meniscus, which is a structure made out of fibrous cartilage that reduces the friction in a joint. It also helps to disperse the weight in a load-bearing joint more evenly in order to avoid putting too much pressure on any one area of the joint.

I'm pretty sure many of you have heard of the meniscus, at the very least indirectly. Many times, when an athlete has 'torn cartilage' in the knee, it's not just any old cartilage that has been torn - it's specifically a torn meniscus.

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