Articulations: Structure and Function of Joints

Chapter 8: Articulations

Introduction to Articulations

Articulations, or joints, are anatomical structures where two or more bones meet. They play a crucial role in movement, stability, and growth within the skeletal system.

• Definition: An articulation is the site where two bones are joined together.

• Importance: Joints are essential for enabling movement, providing stability, and allowing bones to lengthen during development.

Functions of Joints

• Connect Bones: Joints physically link bones together, forming the framework of the skeleton.

• Enable Movement: Muscles and tendons exert force across joints, allowing for a wide range of movements.

• Provide Stability: Joints that allow little or no movement are highly stable, protecting underlying structures (e.g., skull joints).

• Allow Long Bones to Lengthen: The epiphyseal plate is a temporary joint that enables long bones to grow during development.

Classification of Joints

Functional Classification

Joints are classified by the degree of movement they allow and their stability.

• Synarthrosis: No movement between articulating bones; provides maximum stability.

• Amphiarthrosis: Small amount of movement; offers a balance between stability and mobility.

• Diarthrosis: Freely moveable joints; allow a wide variety of movements but are less stable.

Structural Classification

Joints are also classified by the type of connective tissue linking the bones and the presence or absence of a joint cavity.

• Fibrous Joints: Bones united by dense regular collagenous connective tissue; no joint space; functionally synarthroses or amphiarthroses.

• Cartilaginous Joints: Bones connected by cartilage; no joint space; functionally synarthroses or amphiarthroses.

• Synovial Joints: Bones separated by a fluid-filled joint cavity; functionally diarthroses.

Fibrous Joints

General Features

Fibrous joints are connected by collagen fibers, providing stability and permitting little to no movement.

Types of Fibrous Joints

• Sutures: Found between bones of the skull; interlocking projections held by short collagen fibers. Very stable (synarthroses). With age, sutures may fuse to form a synostosis.

• Gomphoses: Joint between a tooth and its alveolus in the mandible or maxilla. The tooth is anchored by the periodontal ligament. Stable synarthrosis.

• Syndesmoses: Articulating bones joined by an interosseous membrane or ligament (dense regular collagenous connective tissue). Found between the radius and ulna (forearm) and the fibula and tibia (leg). These are amphiarthroses, allowing limited movement.

Summary Table: Joint Classifications

Classification	Type of Tissue	Joint Space	Functional Class	Examples
Fibrous	Dense regular collagenous CT	No	Synarthrosis/Amphiarthrosis	Sutures, Gomphoses, Syndesmoses
Cartilaginous	Cartilage	No	Synarthrosis/Amphiarthrosis	Epiphyseal plate, Intervertebral discs
Synovial	Synovial membrane/fluid	Yes	Diarthrosis	Knee, Shoulder, Elbow

Example:

The suture between the parietal and frontal bones of the skull is a fibrous joint, providing stability and protecting the brain.

Additional info: The notes above cover the introductory and foundational aspects of joint classification and fibrous joints. For a complete study guide, further details on cartilaginous and synovial joints, as well as joint movements, would be included in subsequent sections.