Human Anatomy and Physiology Chapter 08: Joints

Human Anatomy and Physiology - Chapter 08: Joints

Why This Matters

  • Understanding joints is crucial for treating injuries (e.g., ankle sprains).

8.1 Classification of Joints

  • Joints (articulations): sites where two or more bones meet.

  • Functions: provide mobility and stability to the skeleton.

  • Classification Types:

    • Structural:

    • Fibrous Joints: no joint cavity, bones connected by fibrous tissue.

    • Cartilaginous Joints: no joint cavity, bones united by cartilage.

    • Synovial Joints: fluid-filled joint cavity allows free movement.

    • Functional:

    • Synarthroses: immovable joints.

    • Amphiarthroses: slightly movable joints.

    • Diarthroses: freely movable joints.

  • Structural classifications are generally more definitive.

8.2 Fibrous Joints

  • Bones joined by dense fibrous connective tissue, usually immovable.

  • Types of Fibrous Joints:

    • Sutures:

    • Interlocking joints of the skull, allow growth during youth.

    • In middle age, they ossify and fuse (synostoses).

    • Syndesmoses:

    • Bones connected by ligaments, movement varies based on fiber length.

    • Examples:

      • Short fibers (little to no movement): inferior tibiofibular joint.

      • Long fibers (more movement): interosseous membrane of radius and ulna.

    • Gomphoses:

    • Peg-in-socket joints, example: teeth in alveolar sockets, connected by periodontal ligament.

8.3 Cartilaginous Joints

  • Bones united by cartilage, lack a joint cavity, and are generally not highly movable.

  • Types of Cartilaginous Joints:

    • Synchondroses:

    • Bones united by hyaline cartilage, mostly synarthrotic.

    • Examples: Epiphyseal plates, cartilage between 1st rib and sternum.

    • Symphyses:

    • Fibrocartilage unites bones, strong and slightly movable.

    • Examples: intervertebral joints and pubic symphysis.

8.4 Synovial Joints

  • Bones separated by a fluid-filled cavity, all are diarthrotic (freely movable).

  • Features of Synovial Joints:

    • Articular Cartilage: Covers ends of bones to prevent crushing injuries.

    • Joint Cavity: Small, fluid-filled space unique to synovial joints.

    • Articular Capsule:

    • Thick fibrous layer and an inner synovial membrane creating synovial fluid.

    • Synovial Fluid:

    • Viscous fluid that lubricates and nourishes articular cartilage, removes debris.

    • Reinforcing Ligaments:

    • Types include capsular, extracapsular, and intracapsular.

    • Nerve and Blood Supply:

    • Nerves detect pain, muscle tone stabilizes joints.

    • Other Features:

    • Fatty pads for cushioning, articular discs to improve joint fit.

Bursae and Tendon Sheaths

  • Bursae: Fluid-filled sacs that reduce friction.

  • Tendon Sheaths: Elongated bursae around tendons subjected to friction.

Factors Influencing Stability of Synovial Joints

  • Shape of Articular Surface: Minor role, shallow surfaces are less stable.

  • Ligament Number and Location: More ligaments create stronger joints.

  • Muscle Tone: Most important for joint reinforcement (e.g., shoulder, knee).

Movements Allowed by Synovial Joints

  • Joints allow multiple planes of movement:

    • Nonaxial: only slipping movements.

    • Uniaxial: movement in one plane.

    • Biaxial: movement in two planes.

    • Multiaxial: movement in all planes.

  • General Types of Movements:

    • Gliding: Flat surfaces sliding (e.g., intercarpal joints).

    • Angular Movements: Involve changes in angle (e.g., flexion, extension).

    • Rotation: Twisting movements around an axis (e.g., shoulder rotations).

Special Movements

  • Supination/Pronation: Rotation of radius and ulna.

  • Dorsiflexion/Plantar Flexion: Movements of the foot at ankle.

  • Inversion/Eversion: Movements of the foot.

  • Protraction/Retration: Movements of the jaw.

  • Elevation/Depression: Movements of the mandible.

  • Opposition: Movement of the thumb touching fingers.

Types of Synovial Joints

  • Six types based on shape and movement:

    • Plane: Flat surfaces.

    • Hinge: Allows flexion and extension (e.g., elbow).

    • Pivot: Allows for rotation (e.g., neck).

    • Condylar: Biaxial movement (e.g., knuckles).

    • Saddle: Fit like a rider and a saddle (e.g., thumb).

    • Ball-and-Socket: Multiaxial movement (e.g., shoulder, hip).

This structured overview summarizes the key aspects of joints from the Human Anatomy and Physiology text, focusing on classifications, structures, movements, and their importance in health and treatment.