ch 9_Articulations_lecture_Mulhern-recorded part I

Chapter 9: Joints

Overview

  • Joints (articulations): connections where two bones meet; site of body movement.

  • Movement involves a trade-off between mobility and strength.

  • Classified using two schemes: Structural (anatomy) and Functional (range of motion).

Classification of Joints

Structural Classifications

  • Fibrous: bones connected by fibrous tissue.

  • Cartilaginous: bones connected by cartilage.

  • Bony (Ossification): two bones fuse together.

  • Synovial: freely movable joints.

Functional Classifications

  • Synarthrosis: immovable joint.

  • Amphiarthrosis: slightly movable joint.

  • Diarthrosis: freely movable joint.

Synarthrosis (Immovable Joints)

  • Very strong with no movement; critical for function.

  • Types include:

    • Suture: found in skull; edges interlock.

    • Gomphosis: connects teeth to bony sockets via periodontal ligament.

    • Synchondrosis: bones bridged by hyaline cartilage (e.g., ribs and sternum).

    • Synostosis: formed when bones fuse (e.g., mandibular bones in infants).

Amphiarthrosis (Slightly Movable Joints)

  • More movable than synarthrosis; stronger than diarthrosis.

  • Types include:

    • Syndesmosis: bones connected by ligaments (e.g., distal tibia-fibula).

    • Symphysis: bones connected by fibrocartilage (e.g., pubic symphysis).

Synovial Joints (Diarthrosis)

  • Freely movable; located at the ends of long bones.

  • Surrounded by joint capsule containing:

    • Inner synovial membrane.

    • Outer fibrous capsule.

    • Synovial fluid that fills the joint cavity.

    • Articular cartilage covering articulating surfaces.

Synovial Fluid

  • About 3 mL, similar to egg yolk.

  • Functions:

    • Lubrication: reduces friction.

    • Nutrient distribution: absorbs/diffuses nutrients and waste.

    • Shock absorption: viscosity increases with pressure.

Structure of a Synovial Joint

  • Components:

    • Quadriceps tendon, patella, joint capsule, synovial membrane, articular cartilage.

  • Accessory structures include ligaments, fat pads, bursa, and meniscus, contributing to joint stability.

Accessory Structures

  • Cartilages: Meniscus (fibrocartilage pad).

  • Fat pads: to protect articular cartilages and fill space during movement.

  • Ligaments: connect bone to bone; support joints leading to potential sprains when overstretched.

  • Tendons: attach muscle to bone (not part of the joint).

  • Bursae: small pockets of synovial fluid for cushioning.

Stabilization of Synovial Joints

  • Prevents damage from excessive movements through:

    • Collagen fibers of the joint capsule and ligaments.

    • Shape of articulating surfaces and menisci.

    • Other support structures (bones, muscles, fat pads, tendons).

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