Lecture Notes on Joints

Introduction to Joints

• Joints enable the human body's flexibility and variety of motion.
• Found where bones meet.
• Classified by:
  • Function: Mobility extent
    • Synarthroses: Immovable
    • Amphiarthroses: Slightly movable
    • Diarthroses: Freely movable
  • Structure:
    • Fibrous: Immovable
    • Synovial: Freely movable
    • Cartilaginous: Range of mobility

Fibrous Joints

• Characteristics: Dense fibrous connective tissue, no joint cavity.
• Types:
  • Sutures:
    • Location: Skull
    • Interlocking fibers connected to periosteum, eventually ossify to synostoses.
  • Syndesmoses:
    • Bones connected by ligaments (e.g., fibula and tibia in the leg).
    • Short fibers prevent movement.
  • Gomphoses:
    • Peg-in-socket joints (e.g., tooth and alveolar socket).
    • Ligament: Periodontal ligament.

Cartilaginous Joints

• Characteristics: Bones connected by cartilage, lack joint cavity, not highly movable.
• Types:
  • Synchondroses:
    • Contain hyaline cartilage (e.g., epiphyseal plate in children, first rib's connection to sternum).
  • Symphyses:
    • Made of fibrocartilage, act as shock absorbers (e.g., intervertebral discs, pelvis).

Synovial Joints

• Characteristics: Have a cavity filled with synovial fluid, allow substantial mobility.
• Features:
  • Articular cartilage protects bone ends.
  • Joint cavity with synovial fluid (lubricant reducing friction).
  • Articular capsule: Synovial membrane and fibrous layer.
  • Reinforcing ligaments, nerves, and blood vessels.
  • Additional structures: Fatty pads, fibrocartilage discs (menisci), bursae, tendon sheaths.

Types of Motion in Joints

• Muscle Attachments: Origin (immovable bone) and insertion (movable bone).
• Movements:
  • Nonaxial: Slipping movements.
  • Uniaxial: One plane.
  • Biaxial: Two planes.
  • Multiaxial: In all three planes of space.

Specific Movements

• Gliding: Flat bone surfaces slip over each other (e.g., wrists).
• Angular: Changes angle between bones.
  • Flexion: Decreases angle (e.g., bending head forward).
  • Extension: Increases angle (e.g., straightening elbow).
  • Hyperextension: Extends beyond normal angle.
  • Abduction: Limb moves away from body midline.
  • Adduction: Limb moves toward body midline.
  • Circumduction: Limb makes circular motion.
• Rotation: Bone turns around its axis (hips, shoulders).
  • Internal and external rotation.

Special Movements

• Supination/Pronation: Radius movement around ulna.
• Dorsiflexion/Plantar flexion: Movements in the foot.
• Protraction/Retraction: Movements of the mandible.

Conclusion

• Introduction to skeletal system completed.
• Next topic: Muscles attached to bones and joints.