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13.9: Skeletal System Joints

Difficulty Level: At Grade Created by: CK-12
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What allows running?

Running. A means of terrestrial locomotion allowing humans and other animals to move rapidly on foot. The knees, which connect one part of the leg to the other, have to allow the legs to move. The knee is a joint, the part of the skeletal system that connects bones.

Joints

A joint is a place where two or more bones of the skeleton meet. With the help of muscles, joints work like mechanical levers, allowing the body to move with relatively little force. The surfaces of bones at joints are covered with a smooth layer of cartilage that reduces friction at the points of contact between the bones.

Types of Joints

There are three main types of joints: immovable, partly movable, and movable.

For a video about these types of joints, go to the link below. http://www.youtube.com/watch?v=SOMFX_83sqk

  • Immovable joints allow no movement because the bones at these joints are held securely together by dense collagen. The bones of the skull are connected by immovable joints.
  • Partly movable joints allow only very limited movement. Bones at these joints are held in place by cartilage. The ribs and sternum are connected by partly movable joints.
  • Movable joints allow the most movement. Bones at these joints are connected by ligaments. Movable joints are the most common type of joints in the body, so they are described in more detail next.

Movable Joints

Movable joints are also known as synovial joints. This is because the space between the bones is filled with a thick fluid, called synovial fluid, that cushions the joint (see Figure below).

A movable, or synovial, joint is protected and cushioned by cartilage and synovial fluid.

There are a variety of types of movable joints, which are illustrated in Figure below. The joints are classified by how they move. For example, a ball-and-socket joint, such as the shoulder, has the greatest range of motion, allowing movement in several directions. Other movable joints, including hinge joints such as the knee, allow less movement.

You can watch an animation of movable joints and how they function at this link:

Types of Movable Joints in the Human Skeleton. Movable joints can move in a variety of ways. Try moving each of the joints indicated in the diagram. Can you tell how their movements differ? Other joints in the human skeleton that are not depicted here include saddle, elipsoid, and plane joints.

Summary

  • Joints are places where two or more bones of the skeleton meet.
  • With the help of muscles, joints allow the body to move with relatively little force.
  • Some joints can move more than others.

Practice I

Use this resource to answer the questions that follow.

  1. Describe the motion of the following joints:
    1. shoulder,
    2. knee,
    3. neck,
    4. wrist.

Practice II

Review

1. Define immovable joint, and give an example of bones that are connected by this type of joint.

2. Describe the movement of a pivot joint, such as the elbow.

Notes/Highlights Having trouble? Report an issue.

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Vocabulary

TermDefinition
ball-and-socket joint Movable joint with the greatest range of motion, allowing movement in several directions; examples include the shoulder.
collagen Protein fibers in the extracellular matrix of bone and cartilage.
hinge joint Movable joint allowing less movement than a ball-and-socket joint; examples include the knee.
immovable joint Joint that does not allow movement because the bones at these joints are held securely together by dense collagen.
movable joint Joint that allows the most movement; bones at these joints are connected by ligaments.
partly movable joint Joint that allows only very limited movement; held in place by cartilage.
synovial fluid Fluid that cushions a synovial joint.
synovial joint A moveable joint; space between the bones is filled with synovial fluid.

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Date Created:
Feb 24, 2012
Last Modified:
Aug 28, 2016
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