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  • The joints of the skeleton define the motion of the body and its limitations.

  • Hey welcome to another lesson on Proko. This lesson is about the types of joints in the

  • human body.

  • As artists we really only need to learn the synovial joints, like the shoulder and knee,

  • because they move. Joints that are fibrous and cartilaginous hardly move, and some, like

  • the connection of the two pubic bones, don't move at all. When you're learning how to draw,

  • pay attention to synovial joints, and keep your thoughts away from pubic bones.

  • If you know where the hinge joint is on this foot, you know that it won't do this or this

  • when you stand on your toes. It will do this. We need to know the position of that hinge

  • joint to make squash and stretch look like the real thing.

  • Synovial Joints

  • There are 6 types of synovial joints. They have varying shapes, but the important thing

  • about them is the movement they allow. Joints determine what positions our bodies can take.

  • We learn them to invent poses. And we learn the limits to stretch the limits.

  • The 6 types of synovial joints are: Hinge, Pivot, Ball & Socket, Ellipsoid, Saddle, and

  • Plane. Let's go through them one by one.

  • Hinge

  • The hinge is a very simple joint. It allows movement only on one axis. It's structure

  • prevents rotation this way, or this way. The head of one bone wraps around the cylindrical

  • head of the other, allowing a very stable rotation this way.

  • Going back to the terminology from last week, the hinge joint allows flexion and extension.

  • That's it! Thats all it does, but it does it well. Like the hinges on a door, allow

  • it only to open or close. The best example of it is the elbow. Here's the rotation on

  • a simplified skeleton. Flexion and extension.

  • So if the elbow only allows flexion and extension, how is it that we are able to twist the forearm?

  • Well, let's take a look at the next joint..

  • Pivot

  • The pivot joint also allows rotation at only one axis. However, it rotates along the long

  • axis. A cylindrical bone fits into a ring of bone and ligament, like with the radio-ulnar

  • joint just below the elbow. The cap on the radius bone fits nicely into this notch on

  • the ulna bone. Ligaments complete the ring, holding the bone in place and allow the radius

  • only to rotate inside of it.

  • The result on the forearm is what we call pronation and supination. During pronation,

  • the base of the radius rotates over and around the head of the ulna. The ulna stays relatively

  • still. Remember, the hinge joint at the elbow, prevents the ulna from twisting. So all of

  • that twisting happens at the radius.

  • And by the way, the distal joint of the ulna and radius is also a pivot joint. The combination

  • of the pivot at the top and at the bottom creates that twisting motion for pronation

  • and supination.

  • Ball & Socket

  • The ball & socket is the champion of all joints. Hooray for the ball and socket! It's structure

  • is just like how it sounds. A ball inside of a socket. This simple and effective structure

  • allows it to move in all axes - flexion, extension, abduction, adduction, rotation, and circumduction.

  • The two ball and socket joints of the body are at the hip and the shoulder. The hip has

  • a deep socket, which gives it stability, but limits some range of motion. The shoulder

  • joint has a shallower socket, which gives it greater range of motion, but takes away

  • some stability. Maybe that's why a dislocated shoulder is so common.

  • Ellipsoid

  • The ellipsoid joint is very similar to a ball & socket. However, the ligaments and its oval

  • shape prevent rotation. But it still has the ability to rotate on two axes, which allows

  • flexion/extension, abduction/adduction, circumduction. Circumduction is just a combination of all

  • the others in a circular motion.

  • The ball, or oval head also slides inside the socket. When it rotates along the wider

  • plane, you can see how it pops out too much from the socket. So, it slides in back to

  • center.

  • A great example of an ellipsoid joint is the wrist, aka radiocarpal joint. The group of

  • carpal bones rotate inside the socket of the radius.

  • Saddle

  • The saddle joint is similar to the ellipsoid, but the rotation is limited mostly because

  • of the bone structure. The structure of the saddle is very interesting. Both bones have

  • a concave and convex surface. Convex means the surface sticks out, like a hill. Concave

  • means the surface curves in, like a hole or a cave. The concave plane of one fits on the

  • convex plane of the other. It's like a 3D yin yang! Or a cowboy on a horse! The saddle

  • makes the bottom piece and the cowboy's legs make the top piece.

  • The legs of the top piece, which wrap around the body of the bottom piece allow a rotation

  • this way. The body of the top piece can glide inside of the legs of the bottom piece.

  • So, this unique structure allows the joint to flex, extend, abduct, adduct, circumduct,

  • and very slightly rotate.

  • An example of a saddle joint on the body is the carpometacarpal joint of the thumb.

  • Let's see that baby in action!

  • Plane

  • Finally, the plane joint. Not really as interesting as the others, but deserves our love anyway.

  • It's basically two flat-ish surfaces, one on top of the other. These surfaces can glide

  • or rotate.

  • They usually come in groups, like the carpals of the hand and the tarsals of the foot. Ligaments

  • hold these bones together, but might allow some rotation and gliding.

  • Another plane joint is the acromioclavicular joint. That's the one between the clavicle

  • and acromion process of the scapula. When we elevate the shoulder, the angle in here

  • will adjust to keep the scapula vertical.

  • The Spine

  • I mentioned in the beginning that cartilaginous joints are not important for artists, except

  • in one, big, important case: your spine. We'll talk about that, in the next lesson.

  • Assignments

  • For this lesson, there's two assignments.

  • The first assignment is to find these joints on yourself and study the movement.

  • I've posted 6 close-up images of Skelly's joints in the description under this video.

  • Your second assignment is to draw them as simple versions. When you try to put them

  • into perspective, you may find it difficult, but I will have Marshall help you understand

  • how to do it. Post your drawings in the facebook group, at facebook.com/groups/anatomy4artists.

  • Marshall, the perspective master will help to critique your assignments in the facebook

  • group. Later, Marshall will do a demo to show you how to simplify your forms and move them

  • around.

  • Last week we studied the language of anatomy. Just looking at a long list of terms can be

  • daunting and difficult to remember. That's why I put together a PDF ebook that visually

  • defines all these terms. This ebook is available as a premium feature at proko.com/anatomy.

  • This week I've included another PDF ebook showing which of the 6 types every joint in

  • the body is classified as. And again it's shown visually, rather than just a list, so

  • you can print these out as reference.

  • Another premium feature you'll see this week when you login to your account, is a 3D model

  • of Robo Skelly. This is a skeleton with simplified forms. Simplified forms are a lot easier to

  • understand, to remember and are more practical to apply to your drawings. So, you can zoom

  • in and rotate around Robo Skelly directly in your browser. This will help you with the

  • assignment this week and upcoming lessons when we study the skeleton in detail.

  • To get all the premium features, go to proko.com/anatomy

The joints of the skeleton define the motion of the body and its limitations.

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B2 中高級

關節的6種類型--藝術家的人體解剖學。 (The 6 Types of Joints - Human Anatomy for Artists)

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    vulvul 發佈於 2021 年 01 月 14 日
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