Freely movable joints are called diarthroses.
Diarthroses, also known as synovial joints, represent the most common type of joint found in the adult human body. Their defining characteristic is the presence of a joint cavity, a space between the articulating bones, which allows for a wide range of motion.
Key Features of Diarthroses:
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Articular Cartilage: The ends of the bones within a diarthrosis are covered with hyaline cartilage, referred to as articular cartilage. This smooth, resilient tissue reduces friction during movement and helps to protect the underlying bone.
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Joint Cavity: A fluid-filled space separating the articulating bones. This cavity contains synovial fluid.
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Synovial Fluid: This viscous fluid lubricates the joint, reducing friction and providing nutrients to the articular cartilage. It is produced by the synovial membrane.
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Synovial Membrane: This membrane lines the joint cavity (except for the articular cartilage) and produces synovial fluid.
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Articular Capsule: A fibrous connective tissue structure that surrounds the joint, providing support and stability. It is continuous with the periosteum of the articulating bones. The articular capsule may contain ligaments.
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Ligaments: Strong bands of connective tissue that connect bones to each other, further stabilizing the joint and preventing excessive movement.
Examples of Diarthrotic Joints:
- Shoulder Joint: Allows for a wide range of motion, including flexion, extension, abduction, adduction, and rotation.
- Hip Joint: Provides stability and supports weight-bearing while allowing for a significant range of motion.
- Knee Joint: A complex hinge joint that allows for flexion and extension, as well as some rotation.
- Elbow Joint: Primarily a hinge joint, allowing for flexion and extension.
- Wrist Joint: Allows for flexion, extension, abduction, and adduction.
In summary, diarthroses are freely movable joints characterized by a joint cavity filled with synovial fluid, articular cartilage, and supporting structures like ligaments and the articular capsule. They are essential for a wide range of movements in the human body.
