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Chapter 8 The Joints Part A
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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
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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
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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
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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)
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Joints Functional Structural Diarthro. Synarthro. Amphiarthro. Fibrous
Cartilage Synovial Sutures Symphysis Gomphoses Synchondroses Syndesmoses
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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
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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)
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Fibrous Structural Joints: Sutures
Figure 8.1a
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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)
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Fibrous Structural Joints: Syndesmoses
Figure 8.1b
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Fibrous Structural Joints: Syndesmoses (Radius & Ulna)
Figure 7.24
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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
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Tooth: Periodontal Ligament
Figure 23.11
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Structural Cartilaginous Joints
Binding material: Cartilage Presence of cavity: Lack a joint cavity Types: Synchondroses Symphyses
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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)
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Cartilaginous Joints: Synchondroses
Figure 8.2a, b
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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
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Cartilaginous Joints: Symphyses
Figure 8.2c
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Cartilaginous Joints: Symphyses
Figure 7.27a
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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
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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
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Synovial Joints: General Structure; cont’d.
Synovial fluid: Blood filtrate Produced by the synovial membrane capillaries Reinforcing ligaments: Capsular (intrinsic) Extracapsular Intracpsular
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Synovial Joints: General Structure
Figure 8.3a, b
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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
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Synovial Joints: Friction-Reducing Structures
Figure 8.4
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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
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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
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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)
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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
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