Study Notes: Anatomy & Physiology – Joints (Chapter 8)

Joints: Classification, Structure, and Movements

Objectives

• Understand how different joints are classified.

• Learn the anatomical structures of different joints.

• Identify the different types of movements of synovial joints.

Classification of Joints

Structural Classification

Joints, also called articulations, are sites where two or more bones meet. They are classified based on the material binding the bones and the presence or absence of a cavity.

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

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

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

Functional Classification

Joints are also classified by the amount of movement they allow:

• Synarthroses: Immovable joints.

• Amphiarthroses: Slightly movable joints.

• Diarthroses: Freely movable joints (primarily synovial joints).

Fibrous Joints

Types of Fibrous Joints

• Sutures: Rigid, interlocking joints of the skull; allow for growth during youth, but ossify in adulthood (synostoses).

• Syndesmoses: Bones connected by ligaments; movement depends on length of ligament (e.g., distal tibiofibular joint).

• Gomphoses: Peg-in-socket joints (e.g., teeth in alveolar sockets); connected by the periodontal ligament.

Cartilaginous Joints

Types of Cartilaginous Joints

• Synchondroses: Bones united by hyaline cartilage (e.g., epiphyseal plate, joint between first rib and sternum).

• Symphyses: Bones united by fibrocartilage; strong, flexible (e.g., intervertebral joints, pubic symphysis).

Synovial Joints

General Structure

Synovial joints are characterized by the presence of a fluid-filled joint cavity and are the most movable type of joint.

• Articular Cartilage: Hyaline cartilage covering bone ends.

• Joint (Articular) Cavity: Small, fluid-filled space.

• Articular Capsule: Two layers—outer fibrous capsule and inner synovial membrane.

• Synovial Fluid: Viscous, lubricating fluid within the cavity.

• Reinforcing Ligaments: Strengthen the joint.

• Nerves and Blood Vessels: Supply the joint.

Bursae and Tendon Sheaths

• Bursae: Flattened sacs containing synovial fluid; reduce friction between tissues.

• Tendon Sheaths: Elongated bursae wrapped around tendons subjected to friction.

Factors Influencing Stability of Synovial Joints

• Articular Surface Shape: Determines possible movements and stability.

• Ligament Number and Location: More ligaments generally increase stability.

• Muscle Tone: Most important factor; keeps tendons taut.

Movements Allowed by Synovial Joints

Types of Movements

• Gliding: Flat bone surfaces slide over one another (e.g., intercarpal joints).

• Angular Movements: Change the angle between bones.

  • Flexion: Decreases the angle.

  • Extension: Increases the angle.

  • Abduction: Movement away from the midline.

  • Adduction: Movement toward the midline.

  • Circumduction: Limb describes a cone in space.

• Rotation: Bone turns around its own long axis (e.g., rotation of head, humerus, femur).

• Special Movements: Include supination, pronation, inversion, eversion, protraction, retraction, elevation, depression, opposition.

Types of Synovial Joints

Synovial joints are classified by the shape of their articular surfaces and the movements they allow:

• Plane: Nonaxial, gliding movements (e.g., intercarpal joints).

• Hinge: Uniaxial, flexion and extension (e.g., elbow).

• Pivot: Uniaxial, rotation (e.g., proximal radioulnar joint).

• Condyloid: Biaxial, flexion/extension and abduction/adduction (e.g., wrist).

• Saddle: Biaxial, similar to condyloid but allows greater movement (e.g., thumb).

• Ball-and-Socket: Multiaxial, most freely moving (e.g., shoulder, hip).

Table: Structural and Functional Characteristics of Body Joints

Joint Type	Structural Classification	Functional Classification	Examples
Suture	Fibrous	Synarthrosis (immovable)	Skull
Syndesmosis	Fibrous	Amphiarthrosis (slightly movable)	Distal tibiofibular joint
Gomphosis	Fibrous	Synarthrosis	Tooth in socket
Synchondrosis	Cartilaginous	Synarthrosis	Epiphyseal plate
Symphysis	Cartilaginous	Amphiarthrosis	Pubic symphysis
Synovial	Synovial	Diarthrosis (freely movable)	Shoulder, knee, hip

Key Terms and Definitions

• Articulation: Site where two or more bones meet.

• Synovial Fluid: Viscous fluid that lubricates and nourishes joint structures.

• Bursa: Fluid-filled sac that reduces friction between tissues.

• Tendon Sheath: Elongated bursa that wraps around a tendon.

Examples and Applications

• Shoulder Joint: Ball-and-socket synovial joint; allows multiaxial movement.

• Elbow Joint: Hinge synovial joint; allows flexion and extension.

• Intervertebral Joints: Symphysis cartilaginous joints; allow slight movement and absorb shock.

Formulas and Equations

• Range of Motion (ROM): The degree of movement that occurs at a joint, often measured in degrees.

• Joint Stability: Influenced by the following relationship: $\text{Stability} \propto \text{Shape of Articular Surface} + \text{Number of Ligaments} + \text{Muscle Tone}$

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for college-level Anatomy & Physiology students.