Anatomy & Physiology Study Notes: Chapter 9 – Joints

Joints (Articulations)

Introduction to Joints

Joints, or articulations, are locations where two or more rigid elements of the skeleton meet. They play a crucial role in providing movement and stability to the skeleton, and their structure enables resistance to crushing, tearing, and other mechanical forces.

• Definition: A joint (from the Greek root arthro) is a point of contact between bones, cartilage, or teeth.

• Functions: Permit movement, provide stability, and allow for growth of bones.

Classification of Joints by Function

Joints are classified based on the amount of movement they allow:

• Diarthrosis: Freely movable joints (e.g., shoulder, knee).

• Amphiarthrosis: Slightly movable joints (e.g., intervertebral discs).

• Synarthrosis: Immovable joints (e.g., sutures of the skull).

Classification of Joints by Structure

Joints are also classified by their structural characteristics:

• Fibrous Joints: Bones joined by dense connective tissue; no joint cavity.

• Cartilaginous Joints: Bones joined by cartilage; no joint cavity.

• Synovial Joints: Bones separated by a fluid-filled joint cavity; most movable type.

Summary Table: Joint Classes

The following table summarizes the main types of joints, their structural characteristics, examples, and mobility:

Structural Characteristics	Types	Mobility
Adjoining bones united by collagen fibers	1. Suture (short fibers) 2. Syndesmosis (longer fibers) 3. Gomphosis (periodontal ligament)	Immobile (suture, gomphosis); Slightly mobile and immobile (syndesmosis)
Adjoining bones united by cartilage	1. Synchondrosis (hyaline cartilage) 2. Symphysis (fibrocartilage)	Immobile (synchondrosis); Slightly mobile (symphysis)
Adjoining bones separated by a joint cavity, covered with articular cartilage, and enclosed within an articular capsule lined with synovial membrane	1. Plane 2. Hinge 3. Pivot 4. Condylar 5. Saddle 6. Ball-and-socket	Freely movable (diarthrosis); movement depends on joint type

Fibrous Joints

Types of Fibrous Joints

Fibrous joints are connected by dense connective tissue and do not have a joint cavity. They are generally immovable or allow very limited movement.

• Suture: Found only in the skull; bones are tightly bound by minimal fibrous tissue. Example: Coronal suture between frontal and parietal bones.

• Syndesmosis: Bones are connected by ligaments; movement depends on the length of the fibers. Example: Distal tibiofibular joint.

• Gomphosis: Peg-in-socket fibrous joint. Example: Tooth held in its socket by the periodontal ligament.

Functional Significance

• Provide stability and protection (e.g., sutures protect the brain).

• Allow for slight movement where needed (e.g., syndesmosis in the ankle).

Example: Daily Activity

• Example: The knee joint (a synovial joint) is used in walking and provides both movement (flexion and extension) and stability to support body weight.

Additional info: The images referenced in the slides illustrate the anatomical features of each joint type, showing the connective tissue and bone relationships.