Anatomy CH 9

Chapter 9: Articulations (Joints)

Introduction to Articulations

• Definition: A joint (articulation) is the meeting point of rigid elements of the skeleton.

• Terminology: The Greek root "arthro" is commonly used in relation to joints.

Types of Joints

• Examples of Joints:

  • Bone to bone

  • Bone to cartilage

  • Teeth in bony sockets (alveoli)

Structural Classification of Joints

• Basis: Based on material binding bones and presence or absence of a joint cavity.

• Types:

  1. Fibrous Joints: Connected by fibrous material; typically immobile or slightly mobile.

  2. Cartilaginous Joints: Connected by cartilage; lack a joint cavity; slight mobility.

  3. Synovial Joints: Have a joint cavity and allow for significant movement.

Functional Classification of Joints

• Basis: Classified on the movement capabilities.

• Categories:

  1. Synarthrosis: Immovable joints (e.g., skull).

  2. Amphiarthrosis: Slightly movable joints (e.g.,between vertebrae).

  3. Diarthrosis: Freely movable joints (most joints in limbs).

Detailed Overview of Joint Types

1. Fibrous Joints

• Characteristics: No joint cavity; connected by fibrous connective tissue.

• Types:

  • Gomphosis: Teeth in bony sockets connected by periodontal ligament; can allow minor movement.

  • Sutures: Found in the skull; interlocking edges allow for growth during childhood. Become synostosis in middle age (immobilized).

  • Syndesmosis: Bones connected by ligaments; allows slight movement (e.g., between radius and ulna).

2. Cartilaginous Joints

• Characteristics: Bones united by cartilage; no joint cavity.

• Types:

  • Synchondrosis: Hyaline cartilage connects bony ends (immobile), found in epiphyseal plates and rib-sternum connections.

  • Symphysis: Fibrocartilage connects bones, allowing slight movement (e.g., intervertebral discs and pubic symphysis).

3. Synovial Joints

• Characteristics: Most complex type with joint cavity; all are diarthrotic (freely movable).

• Examples: Shoulder, knee, elbow, and temporomandibular joints (TMJ).

Components of Synovial Joints

• Hyaline Cartilage: Covers the ends of bones to absorb compression.

• Joint Cavity: Contains synovial fluid to reduce friction.

• Articular Capsule: Outer fibrous layer + inner synovial membrane (produces synovial fluid).

• Synovial Fluid: Acts as lubricant and dissipates tension.

• Bursae: Fluid-filled sacs that cushion the joint.

Types of Movements in Synovial Joints

• Gliding Movements: Sliding movements (e.g., between carpal and tarsal bones).

• Angular Movements:

  • Flexion and Extension: Decrease or increase angle between bones.

  • Abduction and Adduction: Move away from or toward midline.

  • Circumduction: Movement describes a cone.

• Rotational Movements: Turning around a bone’s axis (medial vs. lateral rotation).

• Special Movements:

  • Elevation and Depression: Upward and downward movement (e.g., shoulders).

  • Dorsiflexion and Plantar Flexion: Foot movements upward and downward.

  • Inversion and Eversion: Sides of the foot moving medially or laterally.

  • Opposition: Thumb touching the tips of fingers.

Factors Influencing Joint Stability

• Articular Surfaces: Generally minor role except in the knee, elbow, and hip.

• Ligaments: More ligaments = increased stability, but excessive stretching can weaken joints.

• Muscle Tone: Most significant factor; keeps tendons tight and stabilizes joints.

• Proprioceptors: Provide feedback about body position, assisting in stability.

Focus on Major Joints

• Shoulder Joint (Glenohumeral Joint): Most mobile but least stable; supported by rotator cuff muscles.

• Knee Joint: Largest and most complex; includes ligaments and menisci for stability.

• Temporomandibular Joint (TMJ): Easily dislocated; only freely movable joint in the skull.

• Elbow Joint: Commonly dislocated; important in motion and stability.

• Hip Joint: Strong but can become weak in flexed positions.

Joint Disorders and Injuries

• Sprains: Damage to ligaments; slow healing due to low vascularization.

• Dislocations: Joints displaced from normal position.

• Torn Cartilage: Common in knees (menisci tears).

• Bursitis and Tendonitis: Inflammation of bursa or tendons.

• Arthritis: General inflammation; different types include:

  • Gouty Arthritis: Painful swelling in joints, often in the big toe.

  • Osteoarthritis: Wear and tear inflammation.

  • Rheumatoid Arthritis: Autoimmune attack on joint tissues.

Conclusion

• Understanding the types, structures, functions, movements, and potential disorders of joints is crucial for studying human anatomy and physiology.