Lec 6 - Study Notes: Anatomy & Physiology – Joints (Articulations)

Chapter 8: Joints (Articulations)

Introduction to Joints

Joints, also known as articulations, are anatomical structures where two or more bones meet. They are essential for providing support and enabling movement in the skeletal system.

• Support and Mobility: Bones are reinforced at joints to allow movement while maintaining structural integrity.

• Types of Connections: Bones may be joined by direct contact or by connective tissues such as cartilage or fibrous tissue.

• Key Terms: Articulation (joint), cartilage, fibrous tissue

Joint Classification

Structural Classification

Joints are classified based on the material binding the bones and the presence or absence of a joint cavity.

• Fibrous Joints: Bones joined by dense regular 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.

Functional Classification

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

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

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

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

Strength versus Mobility

Relationship Between Joint Strength and Mobility

There is an inverse relationship between the strength and mobility of a joint.

• Highly Movable Joints: Less strong, more prone to injury (e.g., shoulder joint).

• Strong Joints: Less movable, more stable (e.g., sutures in the skull).

Example: The shoulder joint is highly mobile but less stable compared to the hip joint.

Types of Joints

Synarthrosis (Immovable Joints)

• Fibrous Synarthroses: Sutures (skull), gomphoses (teeth in sockets).

• Cartilaginous Synarthroses: Synchondroses (epiphyseal plates in children).

Amphiarthrosis (Slightly Movable Joints)

• Fibrous Amphiarthroses: Syndesmoses (distal tibiofibular joint).

• Cartilaginous Amphiarthroses: Symphyses (pubic symphysis, intervertebral discs).

Diarthrosis (Freely Movable Joints)

• Synovial Joints: Most common type; includes hinge, ball-and-socket, pivot, saddle, plane, and condyloid joints.

• Key Features: Joint cavity, articular cartilage, synovial fluid, accessory structures.

Synovial Joint Structure

Basic Components

• Articular Cartilage: Covers bone surfaces, reduces friction.

• Joint Capsule: Encloses joint cavity, lined by synovial membrane.

• Synovial Fluid: Lubricates joint, nourishes cartilage.

• Accessory Structures: Cartilage pads (menisci), ligaments, tendons, bursae.

Accessory Structures

• Menisci: Fibrocartilage pads that improve fit and stability.

• Ligaments: Connect bone to bone, provide stability.

• Tendons: Connect muscle to bone, support joint movement.

• Bursae: Fluid-filled sacs that reduce friction.

Movements of Synovial Joints

Types of Movements

• Angular Motion: Changes angle between bones (flexion, extension, abduction, adduction, circumduction).

• Rotation: Bone pivots around its own axis (medial/lateral rotation, pronation, supination).

• Special Movements: Includes inversion, eversion, dorsiflexion, plantar flexion, opposition, reposition, protraction, retraction, elevation, depression.

Examples of Synovial Joints

• Hinge Joint: Allows flexion and extension (e.g., elbow, knee).

• Ball-and-Socket Joint: Allows movement in all directions (e.g., shoulder, hip).

Specific Joints and Ligaments

Temporomandibular Joint (TMJ)

The TMJ is a unique synovial joint that allows movement of the jaw for chewing and speaking.

• Components: Mandibular condyle, articular disc, joint capsule.

• Movements: Elevation, depression, protraction, retraction, lateral excursion.

• Ligaments: Lateral, sphenomandibular, stylomandibular ligaments.

Intervertebral Ligaments

• Anterior Longitudinal Ligament: Connects anterior surfaces of vertebral bodies.

• Posterior Longitudinal Ligament: Connects posterior surfaces of vertebral bodies.

• Ligamentum Flavum: Connects laminae of adjacent vertebrae.

• Interspinous and Supraspinous Ligaments: Connect spinous processes.

Sternoclavicular Joint

• Ligaments: Sternoclavicular, costoclavicular, interclavicular ligaments.

• Function: Connects the clavicle to the sternum, allows movement of the shoulder girdle.

Table: Joint Classification Overview

Structural Type	Functional Type	Example	Movement
Fibrous	Synarthrosis	Suture (skull)	Immovable
Cartilaginous	Amphiarthrosis	Symphysis (pubic symphysis)	Slightly movable
Synovial	Diarthrosis	Shoulder, knee	Freely movable

Key Equations and Terms

• Synovial Fluid Production: $\text{Synovial fluid} = \text{Filtrate of blood plasma} + \text{secretions from synovial membrane}$

• Range of Motion: $\text{ROM} = \text{Angle of movement between bones at a joint}$

Additional info: Some anatomical details and examples were inferred for completeness and clarity.