Fetal Skull and Fontanelles

• Fontanelles

  • Definition: Soft spots between skull bones covered with fibrous tissue.

  • Allow for skull expansion as the brain grows in a fetus and early childhood.

  • Notable areas:

    • Anterior Fontanelle: Between parietal and frontal bones.

      • Known as the 'soft spot'; can see baby's pulse here.

    • Posterior Fontanelle: Between parietal and occipital bones.

    • Sphenoidal (Lateral) Fontanelle: Between sphenoid, frontal, temporal, and parietal bones.

    • Mastoid Fontanelle: Between temporal, occipital, and parietal bones.

  • Gradual ossification: Typically begins around 24 months but may take years to fully close.

Joints

• Definition: Any location where two bones meet.

• Classification:

  • Functional classification: Based on movement.

    • Synarthrosis: Immovable joint (example: sutures in the skull).

    • Amphiarthrosis: Slightly movable (example: rib connections to the sternum via costal cartilage).

    • Diarthrosis: Freely movable joint (example: hip or shoulder).

  • Structural classification: Based on composition.

    • Fibrous joints: Typically immovable, for example, skull sutures.

    • Cartilaginous joints: Slightly movable, with cartilage between bones (example: pubic symphysis).

    • Synovial joints: Freely movable with a joint cavity.

Synovial Joints

• Characteristics:

  • Joint cavity present, filled with synovial fluid.

  • Articular cartilage: Smooth hyaline cartilage that reduces friction on joint surfaces.

  • Fibrous capsule: Encloses joint, providing stability.

  • Synovial fluid: Lubricates the joint and reduces friction.

  • Ligaments: Dense connective tissue structures connecting bones. Example: ACL (anterior cruciate ligament) in the knee.

• Example: Glenohumeral Joint (Shoulder Joint):

  • Contains fibrous capsule connecting glenoid cavity of scapula to humerus.

  • Synovial membrane: Lines the fibrous capsule and produces synovial fluid.

  • Bursae: Fluid-filled sacs reducing friction where ligaments or tendons may interact with bones.