Right now, the longest section we're going to talk about are synovial or freely movable joints. These are the most complicated of our joints, but they're also the ones that you're most familiar with. So synovial joints allow for large amounts of movement or smooth movement between bones.
They are freely movable. And the type of movement that you get depends on the type of joint you have, but there are a large variety of movements that can occur. Typically, you're going to see articular cartilage covering the ends of the articulating bones.
And between those bones, you'll see a synovial cavity. This synovial cavity has a nerve and blood supply, and synovial joints are then going to be surrounded by and held together by accessory ligaments. So in the structure of a synovial joint, first you're going to have the two or more articulating bones that are going to be covered on the ends by articular cartilage here in gray to prevent wear and tear of the bone.
Then you have the articular capsule. The capsule consists of a fibrous membrane here on the outside and then a synovial membrane here. on the inside that produces synovial fluid.
So inside the synovial cavity, it will be fluid filled with the synovial fluid that is a lubricant in the joint to help prevent wear and tear of the joint. In this cadaver, you can see clearly that synovial cavity. Now many of your synovial joints are going to have bursa and tendon sheaths. The function of this is to prevent friction between the bone and the overlying skin, muscle, or tendons.
So if it's a bursa, it is a sac-like structure, and it's usually filled with synovial fluid, and it cushions body parts. You can see several here in the knee joint. You can see a bursa here in front of the patella.
You can see these pads, which are bursa, that are pretty evident here, also right here. A tendon sheath is basically a bursa, but instead of being a sac, it's like a tube that's wrapped around your tendons. And you can see those here in the hand, the tendon sheaths, very clear.
Now on your synovial joints, you have different types of movements. These include gliding, extension flexion, adduction, abduction, circumduction, and rotation. and special movements that are associated only with certain bones. So in a gliding joint, it's pretty simple.
It occurs on bones that are relatively flat or cuboidal, and the bones slide across one another like the carpals in the hand and wrist. Then you have extension, flexion, and hyperextension. Extension is any movement that's going to open up a joint. For example, on your elbow. When you unbend or extend your elbow, that opens up the elbow joint.
Flexion is going to close a joint. So if you imagine bending your elbow so that your hand comes up towards your shoulder, that closes the angle of the joint. So that's called flexion. Hyper extension is when you overextend the joint more than 90 degrees. So that occurs regularly here in the head, at the neck.
But other joints can be injured if you hyperextend them because the tendons and ligaments are not meant to move that far. So it can damage those. Abduction and abduction.
Abduction, think of adding. It means you're moving an extremity toward the midline or you're adding it to the body. It also applies to your digits.
And, oh, I got those backwards. When you add them, you pull the, close the digits closer together. When you abduct, you take your digits and separate them.
Notice I got those backwards here on this PowerPoint, but I'll fix it on the one for you. And then finally, abduction is the opposite. It's moving an extremity away.
And this applies to the hand too, if you bend it at the wrist. So looking at what your thumb does, you can add. or abduct it away from the body. Circumduction is where your limb rotates in a circle.
So this includes abduction, adduction, flexion, rotation. But circumduction requires a large variety of movements, and it only applies to your arms and legs. Rotation can apply to your head, where your head rotates right and left, like you're shaking your head no. But it can also apply to your arms. and legs.
So if you're rotating toward the midline, it's called a lateral, I mean, a medial rotation. If you're rotating away from the midline, it's a lateral rotation. Your jaw is one of the joints, the temporomandibular joint that can have special movements associated with it. So elevation and depression are opening and closing the mouth. So if you think of depression as someone sitting there with their mouth hanging open.
Protraction and retraction is movement of the jaw posteriorly and anteriorly. So protraction is the jaw moving anteriorly. So you can think of that as an underbite.
And then retraction is the opposite with the jaw moving toward the rear or the posterior part of the body. In the hand. If you take your thumb and touch the pads of each of the other fingers, that's called opposition. So we say like we have opposable thumbs as opposed to some of the apes or chimpanzees. And then the hand can also do what's called supination and pronation.
Supination is where the palm faces anteriorly, so anatomic position, or pronation where it faces posteriorly. The foot also has special movement, pointing your toes like a gymnast or a diver. That is what's referred to as plantar flexion.
The opposite of that is pointing your toes upward superiorly toward the head. And that's dorsiflexion. Inversion and eversion are bending at the ankle.
So if your feet, the sole of your foot faces toward the midline, that's called inversion. And if it faces... faces away from the midline.
It's called eversion. All right. Now there's several types of joints, six actually, of synovial joints. You can have plane, hinge, pivot, congenital, saddle, and ball, and socket joints.
And we're going to look at each of those. But on this diagram on the right, you can see the general structure of what they look like. So with a plane joint, this is...
allows gliding movements. And you see this as a good example in your carpals and tarsals, your ankle and wrist bones, where the joint and bones can slide across each other. A hinge joint functions just like a door hinge. So your elbow is a really good example of that.
Where it says uniaxial, that means you can only bend in one direction. And you can only open or close your forearm, which makes sense. A pivot joint is a rotation about an axis.
There's not as many of those in the body. Some examples between the atlas and axis. Remember the atlas is C1 vertebra. The axis is C2 vertebra. And the axis has a structure called a dens that extends upward and is held by a ligament wrapped around it inside the atlas.
And this allows your head to turn left and right or yes and no. You also see it between the radius and the ulna where the radius, the head of the radius, can actually rotate around or pivot around the ulna. Congular joints, an example is the radiocarpal joint, the radius where it connects to the carpals of the wrist.
And this is a gliding movement similar to what's happening with a joystick. And you can see that here. where the stick will move left, right, up and down many different angles.
And that's called a congeloid joint. Saddle joints, the good example is between the trapezium, which is one of your carpal bones, and the first metacarpal on the side of the thumb. So the one bone sits actually on the other bone, very much like something sitting on a saddle. Ball and socket joints are the most movable of all the joints, which also means they're the less stable. When you sacrifice stability to get mobility.
These are your hip and shoulder joints. Those are the only two. And they allow the most rotation, but that also means they're the most unstable. But in this case, the ball fits in a socket very much like a baseball fits inside a baseball glove. Now, what will affect your contact and range of motion?
The structure and shape of the bones that meet. Only some bones can form certain types of joints. How taut. or strong your ligaments are that hold the joint together, the arrangement and the tension of the muscles surrounding the joint, the contact hormones, for example, relaxin that's produced during pregnancy softens the pubic symphysis to allow for more movement during childbirth, and disuse.
The less you use a joint, the tighter the ligaments are going to become, which means the less flexibility you're going to have. Now to look at a few particular joints, you have the temporomandibular joint. That's where the jawbone articulates with the temporal bone of the skull. And for this connection, you have the mandibular fossa in the temporal bone that accepts the condyle of the mandible, the little projection sticking off the top of the mandible. The atlantoaxial joint.
is the joint between the first and second cervical vertebra. In this, the dens of the C2 vertebra, the axis extends upward where it's held in place by a ligament across this pivot joint between the C1 and C2 vertebra. And that allows your head to shake no left and right.
The glenhumeral joint is a ball and socket joint. This is your shoulder joint. So because it's a ball and socket, it has the widest range of motions.
But it also means it's going to be supported by many ligaments and muscles to keep the stability. So the bones that meet there are the clavicle and the scapula, particularly the acromion and coracoid processes of the scapula. And those are going to articulate with the head of the humerus that fits into the glenoid cavity of the scapula. Also in this joint, you have versa, the subacromial subscapular versa, which are shown here, these little packets here in gray between the connecting bones. And then the inside of the glenoid cavity is lined with articular cartilage called the glenoid labrum.
The elbow joint is an example of a hinge joint. because it only allows for flexion and extension of the forearm. It is supported by radial and ulnar ligaments. There's also an annular ligament that actually wraps around the head of the radius to connect it to the pivot joint of the ulna.
Now in the joint itself, you have the projection, the olecranon of the ulna that actually wraps around the back of the humerus and it articulates with the... olecranon fossa of the humerus that lies between the epicondyles of the humerus. These epicondyles connect to the ligaments that hold the M1 joint together. The hip joint is an example of the ball and socket joint. It's between the head of the femur and the acetabulum or the cavity in the pelvic girdle.
It is what we call a multiaxial joint. because you can get multiple types of movement, including moving your legs, anterior or posterior, medial or lateral, or rotating them. So because it's a ball and socket joint, it has the most movement.
That also means it has the less stability because it's held together mainly by ligaments, ligaments that attach from mostly the ischium of the pelvic girdle to the trochanters, particularly the greater trochanter of the femur. Also notice that inside the acetabulum of the pelvis, that socket, you have the acetabular labrum. The knee joint is the largest joint of the body.
It connects the femur with the tibia. It's supported by a lot of ligaments. You have the tibial and fibular collateral ligaments that are located on either side of the leg. And then going through the middle of the knee, it's very interesting. You have the ACL and the PCL, or the anterior and posterior cruciate ligaments.
You can actually see those better here in this superior view. Notice that the anterior or the ACL connects the tibia and it crisscrosses back to the femur in the back. And then the PCL goes from the tibia in the back to the femur in the front. So the ACL and the PCL actually make kind of cross like an X in the middle of the knee. And so they keep the femur from moving anterior or posterior.
And then you have your side ligaments, your tibial and fibular ligaments that control the stability of the femur on the tibia with left to right sliding. Also notice that you have meniscuses or menisci, which are connective tissue found between the femur and the tibia. And they basically give you padding and support. The tallow cruel.
joint or the ankle joint is a uniaxial hinge joint between the tibia and the talus, the largest of your ankle, but well, I guess calcaneus is technically larger, but one of the larger two tarsal bones. Now you can move your foot more than just this single hinge, but this one allows for dorsiflexion and plantar flexion. The movements for eversion and inversion occur due to sliding between the talus, capanus, and other tarsals, but not between the ankle and the tibia.
Now your ankle is stabilized by ligaments, particularly those that run from the talus to the medial and lateral malleolus. The medial malleolus being on the tibia, the lateral malleolus on the fibula. Those are the bumps of the ankle that you can see.