Articulation: Definition, Structure and Types of Joints
Introduction
In human anatomy, articulation refers to the site where two or more bones meet, or where a bone meets another skeletal structure such as cartilage. These sites are called joints.
Articulations connect different parts of the skeleton, provide stability and allow movement where required. Some joints permit almost no movement, while others allow a wide range of motion.
For example, the joints between the bones of the skull provide stability and protection, whereas the shoulder joint allows the arm to move in several directions.
[IMG 1 — Horizontal labelled diagram showing examples of articulation at the skull, shoulder, elbow, hip and knee]
Structure of an Articulation
The structure of a joint depends on its type. A typical synovial joint, such as the knee, contains several specialized components that support movement and reduce friction.
Articular cartilage: A smooth layer of hyaline cartilage covers the ends of the bones. It reduces friction and helps distribute forces across the joint.
Joint capsule: A connective tissue envelope surrounds the joint and helps hold the articulating bones together. Its outer fibrous layer provides strength.
Synovial membrane: This membrane lines the inner surface of the joint capsule, except over the articular cartilage. It produces synovial fluid.
Synovial fluid: This fluid lubricates the joint and helps nourish the articular cartilage.
Ligaments: Strong bands of connective tissue connect bone to bone and help stabilize the joint.
Joint cavity: The space between the articulating surfaces contains synovial fluid and allows smooth movement.
[IMG 2 — Horizontal labelled cross-section of a typical synovial joint showing articular cartilage, joint capsule, synovial membrane, synovial fluid, joint cavity and ligaments]
Note: These components describe a typical synovial joint. Fibrous and cartilaginous joints have different structures.
Functions of Articulations
Articulations perform several important functions in the body.
Movement: Joints allow bones to move relative to one another. For example, the elbow joint allows the forearm to bend and straighten.
Stability: Joints and their supporting ligaments help maintain the alignment of bones during standing and movement.
Support and weight transfer: Joints such as the hip and knee help transfer body weight through the lower limbs during walking.
Reduction of friction: In synovial joints, articular cartilage and synovial fluid help reduce friction between moving surfaces.
Relationship Between Articulation and Joint Classification
Joints can be classified structurally according to the tissue connecting the bones and functionally according to the degree of movement they permit.
Structural classification | Functional relationship | Example |
|---|---|---|
Fibrous joint | Usually immovable or slightly movable | Skull sutures |
Cartilaginous joint | Immovable or slightly movable | Epiphyseal plate, pubic symphysis |
Synovial joint | Freely movable | Shoulder, hip and knee |
The relationship is not absolute in every case, but it provides a useful overview of how joint structure relates to movement.
Key Concepts
Articulation is the site where bones or other skeletal structures meet.
Joints connect skeletal components and contribute to movement, stability and support.
Synovial joints contain articular cartilage, a joint cavity, synovial fluid and a joint capsule.
Joint structure influences the amount and type of movement possible.
In summary, articulations connect the components of the skeleton and help the body maintain stability while allowing movement. Their structures vary according to their functions, from the rigid connections of the skull to the freely movable joints of the limbs.