Chapter 8 The Joints Part A

Objectives: Classify the types of joints in the body Give examples for the different types of joints Label the parts of a typical diarthrotic joint List types of diarthrotic joints with examples List and identify the types of movement allowed by diarthrotic joints

Joints (Articulations) Are the weakest parts of the skeleton Articulation: Site where two or more bones meet Functions of joints Hold the skeleton together Give the skeleton mobility

Classification of Joints: Joints are classified according to: Structure Function Structural classification: Based upon: Material binding bones together Presence or absence of a joint cavity Functional classification: The amount of movement allowed by the joint

Structural and Functional Classes of Joints: Structural classes of joints include: Fibrous Cartilaginous Synovial Functional classes of joints include: Synarthroses (immovable ) Amphiarthroses (slightly movable) Diarthroses (freely movable)

Joints Functional Structural Diarthro. Synarthro. Amphiarthro. Fibrous Cartilage Synovial Sutures Symphysis Gomphoses Synchondroses Syndesmoses

Structural Joints: Fibrous Binding material: Fibrous tissues join bones together Presence of cavity: No joint cavity is present Movement: Most are immovable Types: Sutures Syndesmoses Gomphoses

Fibrous Joints: Sutures Occur: Between the bones of the skull Junctions: Completely filled with short fibers of connective tissue During youth: Sutures bind bones tightly together, but allow growth In middle age: Fibrous tissue ossifies Skull bones fuse Sutures are then called synostoses Movement: Immovable (protective adaptation to the brain)

Fibrous Structural Joints: Sutures Figure 8.1a

Fibrous Joints: Syndesmoses Bones are connected by: A ligament, a cord or band of fibrous tissue or A ligament-like interosseous membrane Movement: Varies from immovable to slightly movable Depends on fiber length Examples include the connection between: The distal ends of the tibia and fibula (short ligament) The radius and ulna (Interosseous membrane)

Fibrous Structural Joints: Syndesmoses Figure 8.1b

Fibrous Structural Joints: Syndesmoses (Radius & Ulna) Figure 7.24

Fibrous Structural Joints: Gomphoses The peg-in-socket fibrous joint Example: Joint between a tooth and its alveolar socket The fibrous connection is: The periodontal ligament

Tooth: Periodontal Ligament Figure 23.11

Structural Cartilaginous Joints Binding material: Cartilage Presence of cavity: Lack a joint cavity Types: Synchondroses Symphyses

Cartilaginous Joints: Synchondroses A plate of hyaline cartilage unites bones All synchondroses are synarthrotic (immovable) Examples include: Epiphyseal plates of children First rib and sternum (manubrium) joint (costal cartilage)

Cartilaginous Joints: Synchondroses Figure 8.2a, b

Cartilaginous Joints: Symphyses Articular bone surfaces: Covered with hyaline cartilage fused to an intervening pad of fibrocartilage Are amphiarthrotic (slightly movable) joints Designed for strength and flexibility Examples: Intervertebral joints Pubic symphysis of the pelvis

Cartilaginous Joints: Symphyses Figure 8.2c

Cartilaginous Joints: Symphyses Figure 7.27a

Structural Synovial Joints Binding material: Hyaline cartilage on opposing bone surfaces Components of the joint cavity Presence of cavity: Presence of a fluid-containing joint cavity Movement: All are freely movable Diarthroses Examples: All limb joints And most joints of the body

Synovial Joints: General Structure All synovial joints have the following features: Articular cartilage: Thin spongy hyaline cartilage on bone surfaces Joint (synovial) cavity: Space containing small amount of synovial fluid Two-layered articular (joint) capsule: Fibrous capsule: External; dense irregular c.t.; continuous with periosteum Synovial membrane: Internal; loose c. t.; covers capsule & internal non-hyaline cartilage surfaces

Synovial Joints: General Structure; cont’d. Synovial fluid: Blood filtrate Produced by the synovial membrane capillaries Reinforcing ligaments: Capsular (intrinsic) Extracapsular Intracpsular

Synovial Joints: General Structure Figure 8.3a, b

Synovial Joints: Friction-Reducing Structures Bursae and Tendon Sheaths: Not part of synovial joints Closely associated with synovial joints Bursae: Flattened, fibrous sacs Lined with synovial membranes Contain a thin film of synovial fluid Common where ligaments, muscles, skin, tendons, or bones rub together Tendon sheath: Elongated bursa Wraps completely around a tendon

Synovial Joints: Friction-Reducing Structures Figure 8.4

Synovial Joints: Stability Stability is determined by three factors: Articular surface shape (minor role): Shallow or noncomplementary surfaces are misfits Ligaments (minor role): Unite bones Prevent excessive or undesirable motion Muscle tone (major role): Low level of contractility in the relaxed state Extremely important in reinforcing: Shoulder & knee joints Arches of the foot

Synovial Joints: Movement Every skeletal muscle is attached to bone or other connective tissue structures Attachment occurs at a minimum of two points Muscle’s origin: Attachment to the immovable bone Muscle’s insertion: Attachment to the movable bone

Synovial Joints: Movement Movement occurs when: Muscles contract across joints Muscle insertion moves toward the muscle origin Movement is described in directional term: Around lines or axis Along planes (transverse, frontal, or sagittal)

Range of Motion allowed by Synovial Joints Nonaxial: Slipping movements only Uniaxial: Movement in one plane Biaxial: Movement in two planes Multiaxial: Movement in or around all three planes