Lecture Notes on Joints

Introduction to Joints

• Joints enable body flexibility and movement where bones meet.
• Joints can be classified by:
  • Function: Refers to the extent of mobility.
    • Synarthroses: Immovable
    • Amphiarthroses: Slightly movable
    • Diarthroses: Freely movable
  • Structure: Refers to anatomical design.
    • Fibrous joints: Generally immovable
    • Cartilaginous joints: Range of mobility
    • Synovial joints: Freely movable

Structural Classification of Joints

Fibrous Joints

• Dense fibrous connective tissue; no joint cavity.
• Types:
  1. Sutures: Found only in the skull, interlocking fibers that ossify to form synostoses.
  2. Syndesmoses: Bones connected by ligaments, e.g., radius and ulna.
  3. Gomphoses: Peg-in-socket, e.g., teeth in alveolar sockets with periodontal ligament.

Cartilaginous Joints

• Bones connected by cartilage; no joint cavity.
• Types:
  1. Synchondroses: Hyaline cartilage, e.g., epiphyseal plate, first rib-sternum connection.
  2. Symphyses: Fibrocartilage, compressible, e.g., intervertebral discs, pubic symphysis.

Synovial Joints

• Have a fluid-filled cavity; highly mobile.
• Structure includes:
  • Articular Cartilage: Covers bone ends.
  • Joint Cavity: Contains synovial fluid for lubrication.
  • Articular Capsule: Composed of synovial membrane and fibrous layer.
  • Reinforcing Ligaments, Nerves, and Blood Vessels.
  • Additional Features: Some have fatty pads, menisci, bursae, and tendon sheaths.

Types of Motion in Joints

• Muscles: Origin (immovable bone) and insertion (movable bone) facilitate movement.

• Movement Axes:

  • Non-axial: Slipping movements.
  • Uniaxial: Movement in one plane.
  • Biaxial: Movement in two planes.
  • Multiaxial: Movement in all three planes.

• Types of Movements:

  • Gliding: Flat bone surfaces slide over each other.
  • Angular: Changes angle between bones.
    • Flexion: Decreases angle
    • Extension: Increases angle
    • Hyperextension: Beyond normal range
    • Abduction: Away from midline
    • Adduction: Toward midline
    • Circumduction: Circular movement
  • Rotation: Bone turns around own axis.
    • Internal or external rotation

• Special Movements:

  • Supination and Pronation (forearm)
  • Dorsiflexion and Plantar flexion (foot)
  • Protraction and Retraction (mandible)

Conclusion

• This overview of joints sets the foundation for understanding muscles and the mechanics of the human body.