Study Notes on Chapter 8: The Skeletal System: Articulations

Chapter 8: The Skeletal System: Articulations

Introduction

• Definition of Joints (Articulations)

  • Joints are connections between bones that may or may not permit movement.

  • Involved structures: Cartilage, synovial fluid, and dense connective tissues hold joints together.

• Functional Classification of Joints

  • Joints are classified by the degree of movement they allow:

  • Immovable or slightly movable joints are typically found in the axial skeleton.

  • Freely movable joints are more common in the appendicular skeleton.

Classification of Joints

Functional Classification of Articulations

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• Table 8.1: Functional Classification of Articulations
  

  Functional Category	Description	Example
  SYNARTHROSIS	No movement	Suture, Gomphosis
  AMPHIARTHROSIS	Little movement	Syndesmosis, Symphysis
  DIARTHROSIS	Free movement	Synovial joints
  Structural Classification of Articulations

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  • Table 8.2: Structural Classification of Articulations
    

    Structure Type	Functional Category	Example
    BONY FUSION	Synostosis	Synarthrosis
    FIBROUS JOINT	Suture, Gomphosis, Syndesmosis	Synarthrosis, Amphiarthrosis
    CARTILAGINOUS JOINT	Synchondrosis, Symphysis	Synarthrosis, Amphiarthrosis
    SYNOVIAL JOINT	Monaxial, Biaxial, Triaxial	All diarthroses
    Types of Joints

    Synarthroses (Immovable Joints)

    • Sutures:

      • Found only in the skull.

      • Bones interlock and are held together by short, dense connective tissue fibers.

    • Gomphosis:

      • The joint between a tooth and the alveolar fossa of the maxillae or mandible.

      • Periodontal ligaments connect the tooth to the bone.

    • Synchondrosis:

      • Hyaline cartilage separates the ends of the bones.

    • Synostosis:

      • Occurs when bones fuse to form one bone.

    Amphiarthroses (Slightly Movable Joints)

    • Syndesmosis:

      • Bones connected by relatively long connective tissue ligaments.

    • Symphysis:

      • Bones are joined by a fibrocartilage pad.

    Diarthroses (Freely Movable Joints)

    • Synovial Joints:

      • Typically located at the ends of long bones in the upper and lower limbs.

      • Characteristics of Synovial Joints:

      • Joint capsule

      • Articular cartilages

      • Joint cavity filled with synovial fluid

      • Synovial membrane lining the joint capsule

      • Accessory structures (ligaments, tendons)

      • Sensory nerves and blood vessels

    • Functions of Synovial Fluid:

      • Lubricates the surfaces of the articular cartilages.

      • Nourishes chondrocytes within articulating cartilage due to pressure changes during joint activity.

      • Acts as a shock absorber by distributing pressure.

    Articular Form and Function

    Types of Movement

    • Linear Movements: Movement in a straight line.

    • Angular Movements: Changes in angle between body parts.

    • Rotation: Movement about an axis.

    • Special Movements: Unique movements at specific joints.

    Special Movements

    • Ankle Movements:

      • Eversion/Inversion: Movement of the foot.

      • Dorsiflexion/Plantar Flexion: Flexing and extending the ankle.

    • Vertebral Movements:

      • Lateral flexion: side bending motion of the spine.

    • Thumb Movements:

      • Opposition and Reposition: Unique thumb motion.

    Additional Special Movements

    • Protraction: Movement anteriorly in the horizontal plane.

    • Retraction: Movement posteriorly in the horizontal plane.

    • Elevation: Movement cranially in the vertical axis.

    • Depression: Movement caudally in the vertical axis.

    Angular Movements

    • Abduction: Movement away from the midline of the body.

    • Adduction: Movement toward the midline.

    • Flexion: Decreasing the angle between body parts.

    • Extension: Increasing the angle.

    • Circumduction: Circular movement that combines flexion, extension, abduction, and adduction.

    Structural Classification of Joints

    • Plane joints: Nonaxial joints allow for gliding movements.

    • Multiaxial joints: Allow movement in multiple axes (e.g., Ball and socket joints).

    • Hinge joints: Allow flexion and extension.

    • Pivot joints: Allow rotational movements, e.g., between the first two cervical vertebrae.

    • Condylar joints: Allow for flexion/extension and abduction/adduction.

    • Saddle joints: Allow for biaxial movements.

    Representative Articulations

    Movements of the Vertebral Column

    • Possible movements include:

      • Anterior flexion (bending forward)

      • Extension (bending backward)

      • Lateral flexion (bending to the side)

      • Rotation (twisting)

    Table of Axial Skeleton Articulations

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    • Table 8.3: Articulations of the Axial Skeleton
      

      Element	Joint Type	Type of Articulation	Movements
      Skull	Various	Synarthroses (suture or synostosis), Gomphosis	None
      Vertebral Column	Intervertebral	Amphiarthrosis	Slight movement
      Atlanto-occipital	Diarthrosis	Condylar diarthrosis	Flexion/extension
      Hip bones/femur	Ball-and-socket diarthrosis	Flexion/extension, adduction/abduction
      Knee	Complex, functions as hinge	Flexion/extension
      Aging and Articulations

      • Rheumatism: Pain and stiffness affecting the skeletal and muscular systems.

      • Arthritis: Includes all rheumatic diseases affecting synovial joints.

      • Both conditions are common among older individuals, reflecting the aging of the skeletal system.

      Bones and Muscles

      • The skeletal and muscular systems are structurally and functionally interdependent, forming a single musculoskeletal system.