In this lesson, you will learn about the types, structures, and movements of the joints of the human body. Specifically, this lesson will cover:
1. Types of Joints
Joints are areas of contact between bones in the body, and there are many different types. Ligaments, a type of dense connective tissue, connect the bones at those joints and help to stabilize them as well. Tendons are the connective tissue holding your muscles to your bones.
There are three types of joints in the body: Synovial, fibrous, and cartilaginous.
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- Joint
- A structure that is formed by two or more bones joining together; are held together by ligaments, cartilage or dense-fibrous tissue.
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- Ligament
- A structure composed of dense irregular connective tissue that holds bones together within synovial joints.
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- Tendon
- A tough band of fibrous connective tissue that usually connects muscle to bone.
1a. Synovial Joints
Synovial joints are the most common type of joint in the body. They contain a cavity filled with synovial fluid, which separates the bones. Synovial joints allow for a wide range of motion.
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EXAMPLE
You're able to flex and extend your knee. The knee joint is a type of joint that allows for that range of motion.
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- Synovial Fluid
- Fluid found within synovial joints to reduce wear and tear and to nourish the structures inside of the joint capsule.
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- Synovial Joint
- The most common joint in humans and also the most complex; contains two key characteristics: Surrounded by a joint capsule and contains synovial fluid; also the most highly moveable joint in humans.
1b. Fibrous Joints
In a fibrous joint, there is no cavity between the bones. The bones are joined by a connective tissue that doesn't allow for very much movement.
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EXAMPLE
Your skull is made up of over a dozen type of bones, but those bones are connected by fibrous joints called sutures.
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- Fibrous Joint
- A joint where two or more bones are fused together by tough, fibrous connective tissue (example: skull sutures); this is the least moveable joint of the body.
1c. Cartilaginous Joints
A cartilaginous joint is a type of joint in which cartilage fills the space between bones. This allows for slight movement.
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EXAMPLE
Think of the bones in the spine. In between each of those, there are little pads of cartilage. This eliminates some of the friction between the bones and also allows for a slight bit of movement.
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- Cartilaginous Joint
- A joint where two or more bones are held together by a piece of cartilage (example: vertebrae or pubic bones); these joints are slightly moveable.
2. Types of Motion
Let’s take a more in-depth look at synovial joints. This type of joint allows for a wide range of motion. The different types of motion are:
2a. Flexion and Extension
Flexion and extension are the motions made when bending and straightening. Flexion happens when you flex a muscle to bend a joint. Extension happens when you relax the muscle and let the joint straighten.
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- Flexion
- A type of movement allowed primarily by synovial joints in which an appendage is able to bend; for example, flexion of the bicep muscle pulls the forearm upward by allowing it to bend at the elbow.
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- Extension
- A type of movement allowed primarily by synovial joints in which an appendage is straightened from a flexed position; for example, extension of the arm from a flexed position will return it to its normal resting position.
2b. Rotation and Circumduction
Rotation can occur at synovial joints. To get an example of this type of movement, hold your arm straight out and twist it around its axis. Circumduction happens when an appendage moves in a circular motion. If you do an arm circle, this is an example of circumduction.
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- Rotation
- A type of movement allowed primarily by synovial joints in which an appendage pivots about its axis; holding the arm straight out and twisting it on its axis is an example of rotation.
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- Circumduction
- A type of movement allowed primarily by synovial joints in which an appendage moves in a circular motion; doing arm circles in which the arm moves in a large circular pattern like a windmill is an example of circumduction.
2c. Supination, Pronation & Gliding
Pronation and supination can be demonstrated by your hands and forearms. When you turn your palm and forearm to face upwards or toward your front, this is supination. When you turn them to face down or toward your back, this is pronation.
The joints in your wrist also allow for gliding. You can wave your hand back and forth as the joints in your wrist enable this gliding motion.
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- Supination
- A type of movement allowed primarily by synovial joints in which the forearm and palm face upward or toward your front.
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- Pronation
- A type of movement allowed primarily by synovial joints in which the forearm and palm face downward or toward your back.
2d. Abduction and Adduction
Abduction and adduction are also possible. If you lift your arm straight up away from your center, you are abducting it. If you lower it back down to your side, you are adducting it.
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- Abduction
- A type of movement allowed primarily by synovial joints in which an appendage is moved away from the body’s center; lifting your arm up and away from your side is an example of abduction.
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- Adduction
- A type of movement allowed primarily by synovial joints in which an appendage moves closer to the body’s center; lowering your arm closer to your side from a lifted position is an example of adduction.
The contact points between your bones are called joints. There are three main types of joints in your body: Synovial, cartilaginous, and fibrous joints. Synovial joints allow for the widest range of motion.
Keep up the learning and have a great day!
