Chapter 9 - Articulations (Joints) Notes

Chapter 9 - Articulations (Joints)

Overview of Articulations

• Articulations (Joints): Specialized structures that determine the direction and distance of movement between bones.
• Range of Motion (ROM):
• Joint strength decreases as mobility increases.
• Example: The shoulder exhibits the greatest mobility but is also the most prone to dislocation and injury.

Functional Categories of Joints

1. Synarthrosis (No movement)

• Characteristics: Bony edges are closely opposed, may interlock.
• Purpose: Prevent movement for stability in certain areas.
• Example Types:
  • Suture: Located in the skull; consists of interlocked bones bound by dense fibrous connective tissue.
  • Gomphosis: Binds teeth to their sockets with periodontal ligaments.
  • Synchondrosis: A rigid cartilaginous bridge, e.g., between first pair of ribs and sterilum, or epiphyseal cartilage in long bones.
  • Synostosis: Fused, immovable joints (e.g., frontal suture of the skull).

1. Amphiarthrosis (Little movement)

• Allows more movement than synarthroses but is stronger than freely movable joints.
• Examples:
  • Syndesmosis: Bones connected by ligaments (e.g., distal tibia-fibula connection).
  • Symphysis: Bones connected by a pad of fibrocartilage (e.g., pubic symphysis).

1. Diarthrosis (Free movement)

• Types: Also known as Synovial joints, categorized based on planes of motion:
  • Monaxial: Movement in one plane (e.g., elbow, ankle).
  • Biaxial: Movement in two planes (e.g., ribs, wrist).
  • Triaxial: Movement in three planes (e.g., shoulder, hip).

Synovial Joint Structures

• Articular Cartilage: Provides protection and reduces friction at joints.
• Articular Capsule: Surrounds joints and provides stability.
• Synovial Membrane: Lines the joint and produces synovial fluid.
• Synovial Fluid: Lubricates the joint and nourishes cartilage.
• Joint Cavity: Space within the joint filled with synovial fluid.

Accessory Structures in Synovial Joints

• Meniscus: A fibrocartilage pad that improves fit of bone ends and absorbs shock.
• Fat Pads: Local masses of adipose tissue that protect articular cartilage and act as packing material.
• Accessory Ligaments and Tendons:
• Support and strengthen joints.
• Tendons connect muscle to bone; help facilitate movement.
• Bursae: Sacs of synovial fluid that reduce friction.

Stabilizing Factors

• Joint capsules and ligaments (collagen fibers) limit range of motion to prevent injuries.
• The shape of articulating surfaces, along with menisci, also restrict movement in certain directions.
• Other structures like bones, muscles, and fat pads contribute to stability.

Joint Injuries

• Dislocation (Luxation): Complete dislocation causing damage to articular cartilage and ligaments.
• Subluxation: Partial dislocation.
• Sprains: Injuries to ligaments.
• Strains: Injuries to muscles or tendons.

Types of Dynamic Motion of the Skeleton

• Linear Motion: Gliding movements.
• Angular Motion: Includes movements that increase or decrease angle at joints.
• Circumduction: Circular movement around a joint.
• Rotation: Movement around an axis; includes internal and external rotation.

Angular Motion Examples

• Flexion: Decrease angle at a joint.
• Extension: Increase angle at a joint.
• Abduction: Movement away from the midline.
• Adduction: Movement toward the midline.

Special Movements

• Dorsiflexion: Lifting the foot upward.
• Plantarflexion: Pointing the toes downward.
• Opposition: Movement of the thumb toward the fingers.
• Lateral Flexion: Bending sideways.
• Protraction: Moving a part forward.
• Retraction: Moving a part backward.
• Elevation: Raising a body part.
• Depression: Lowering a body part.