Bone Articulations and Movement Articulations: Definition Classification of Joints: Functional classification Structural classification Synovial Joints Terminology of Movements

Articulations Articulations (or joints) are places where two or more bones meet - required if motion is to occur - structure and function are interrelated - each articulation balances the need for stability versus the need for mobility

Classification of Articulations Joints can be classified based on: - the amount of motion occurring at the joint - the structure and composition of the joint

Classification of Articulations by Function The classification of joints by function (amount of movement) is as follows: - Synarthroses: little or no movement in the joint (extremely strong joint) example: sutures between bones of the skull - Amphiarthrosis: slightly movable joint (strong, yet slightly mobile joint) example: pubic symphysis, intervertebral discs - Diarthrosis: freely movable joint (weakest type) examples: shoulder, elbow, hip, knee joints

Classification of Articulations by Structure There are three types of joints classified by structure: fibrous, cartilagenous, and synovial joints. Fibrous joints - joints in which bones are held together by fibrous CT - sutures: between bones of the skull - synostosis: two bones grow across joint to form a single bone (fusion of two frontal bones) - syndesmosis: gap between bones wider than in suture (interosseus membrane of radio-ulnar joint) - gomphoses: joints in which one end fits into socket of other bone (teeth held in alveoli by periodontal ligaments; fig 24.6)

Cartilagenous Joints Joints in which bones are united by hyaline of fibrocartilage. - synchondroses: cartilagenous joint in which the bones are joined by hyaline cartilage (example: costal cartilage to sternum) - symphysis: cartilagenous joint in which the bones are joined by fibrous cartilage (example: symphysis pubis, intervertebral discs)

Synovial Joints Synovial joints are those that have a joint cavity containing synovial fluid. Since there is a lot of movement in diarthrotic joints, you need: - extra space between bones - a lubricating fluid to reduce friction. Synovial joints are usually found at the ends of long bones.

Structure of Synovial Joints Features of synovial joints: - enclosed in a joint capsule (outer: fibrous capsule, inner: synovial membrane) - the synovial membrane secretes synovial fluid - the ends of bone are covered by articular cartilage (hyaline) - movement can be mono-axial, biaxial, or multiaxial

Bursae In some joints, the synovial membrane may extend outside the joint itself as a pocket, or bursa. A bursa provides protection between bone and tendons, or between skin and bone.

Types of Synovial Joints Synovial joints can be classified based on the shapes of the adjoining articular surfaces: gliding: manubrio-clavicular joint (monoaxial: one plane) hinge: monoaxial (elbow), convex cylinder of one bone into a concavity of another bone

Types of Synovial Joints Pivot: monoaxial, rotation around a single axis Saddle joint: two saddle-shaped articular surfaces at right angles to each other; biaxial

Types of Synovial Joints Ball and socket: ball (head) of one bone into socket of adjacent bone; multiaxial Condyloid (ellipsoid): like a ball and socket, except ball is more oval; biaxial.

flexion: movement in the anterior/posterior plane that reduces the angle between articulating bones

extension: movement in the same plane that increases the angle between bones

plantarflexion: movement of the foot toward the plantar surface (standing on toes) - dorsiflexion: movement of the foot toward the the shin (note that this is really extension of the foot!)

abduction: moving away from the longitudinal axis of the body in the frontal plane (moving back is adduction) circumduction: combination of flexion, extension, abduction, and adduction that moves the limb in a cone

rotation: turning around the longitudinal axis

Upper limb: pronation: rotation of the forearm so that the palm faces posteriorly - supination: rotation of the forearm so that the palm faces anteriorly

Lower limb: - inversion: turning the ankle so that the plantar surface (sole) faces medially eversion: turning the ankle so that the plantar surface faces laterally

protraction: moving a structure anterioly retraction: moving a structure posteriorly

elevation: moving a structure superiorly depression: moving a structure inferiorly

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