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).