Biol 2301 Lecture 10

Joints Overview

  • Joints are where bones meet, also known as articulations.

  • Classified by function (movement) and structure (binding materials).

Joint Classification

  • By Structure:

    • Fibrous: joined by fibrous tissue

    • Cartilaginous: joined by cartilage

    • Synovial: fluid-filled cavities between bones

  • By Movement:

    • Synarthroses: immovable

    • Amphiarthroses: slightly movable

    • Diarthroses: freely movable

Joint Mobility

  • Range of Motion: Normal extent of mobility at synovial joints; measured in degrees.

  • Degrees of Freedom: Number of movement axes at a joint, relevant to synovial joints.

Factors Affecting Joint Stability

  • Articular Surface Shape: Impacts movement.

  • Ligament Count & Position: More ligaments enhance stability.

  • Muscle Tone: Critical for stability, keeps tendons taut.

Fibrous Joints

  • Gomphoses: Peg-in-socket joints (teeth); Synarthrosis.

  • Sutures: Interlocking skull bones; Synarthrosis.

  • Syndesmoses: Connected by ligaments; Amphiarthrosis (e.g., ulna + radius).

Cartilaginous Joints

  • Synchondroses: Articulations with hyaline cartilage; immobile (e.g., epiphyseal plate).

  • Symphyses: Fibrocartilage pad allows slight mobility (e.g., pubic symphysis).

Synovial Joints

  • Enclosed by an articular capsule; classified as diarthroses.

  • Contains synovial fluid for lubrication; features articular cartilage and ligaments.

Bursae & Tendon Sheaths

  • Bursae: Sac-like structures reducing friction.

  • Tendon Sheaths: Elongated bursae around a tendon.

Classification of Synovial Joints

  • Based on movement and structure:

    • Non-axial: Plane joint (gliding).

    • Uniaxial: Hinge and pivot joints.

    • Biaxial: Condyloid and saddle joints.

    • Triaxial: Ball-and-socket joints.

Movements at Joints

  • Gliding: One surface slides over another.

  • Angular Movements: Include flexion, extension, abduction, adduction, circumduction.

  • Rotational Movements: Include medial/lateral rotation, pronation, supination.

  • Special Movements: E.g., dorsiflexion, plantarflexion, eversion, inversion.

Skeletal Muscles as Levers

  • Levers consist of a stiff structure (bone) moving around a pivot (joint).

  • Types of levers:

    • First Class: Resistance and effort act on opposite sides of pivot.

    • Second Class: Both forces act on the same side; mechanical advantage.

    • Third Class: Most common; muscle force and resistance are on the same side.

Specific Joints

  • Temporomandibular Joint: Allows varied motion; involves hinge-like and gliding actions.

  • Glenohumeral Joint: Ball and socket; large head of humerus and shallow glenoid cavity.

  • Elbow Joint: Composite joint with hinge for flexion/extension and pivot for pronation/supination.

  • Hip Joint: Ball and socket; stable due to deep acetabulum and ligaments.

  • Knee Joint: Primarily hinge joint with complex structure involving menisci and ligaments.