Joints

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• Joints

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Objectives Joints

• Define joint or articulation.
• Classify joints structurally and functionally.
• Describe the general structure of fibrous joints.
  Name and give an example of each of the three
  common types of fibrous joints.
• Describe the general structure of cartilaginous
  joints. Name and give an example of each of the
  two common types of cartilaginous joints.
• .Name and describe (or perform) the common types
  of body movements.

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Joints (Articulations)

• Articulationsite where two or more bones meet
• Functions of joints
• Give skeleton mobility
• Hold skeleton together

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Functional Classification of Joints

• Based on amount of movement allowed by the joint
• Three functional classifications
• Synarthrosesimmovable
• Amphiarthrosesslightly movable
• Diarthrosesfreely movable

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Structural Classification of Joints

• Based on material binding bones together and
  whether or not a joint cavity is present
• Three structural classifications
• Fibrous
• Cartilaginous
• Synovial

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Fibrous Joints

• Bones joined by dense fibrous connective tissue
• No joint cavity
• Most are synarthrotic (immovable)
• Three types
• Sutures
• Syndesmoses
• Gomphoses

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Fibrous Joints Sutures

• Rigid, interlocking joints containing short
  connective tissue fibers
• Allow for growth during youth
• In middle age, sutures ossify and are called
  synostoses

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(a) Suture
Joint held together with very short, interconnecti
ng fibers, and bone edges interlock. Found only
in the skull.
Suture line
Dense fibrous connective tissue
Figure 8.1a
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Fibrous Joints Syndesmoses

• Bones connected by ligaments (bands of fibrous
  tissue)
• Movement varies from immovable to slightly
  movable
• Examples
• Synarthrotic distal tibiofibular joint
• Diarthrotic interosseous connection between
  radius and ulna

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(b) Syndesmosis
Joint held together by a ligament. Fibrous tissue
can vary in length, but is longer than in
sutures.
Fibula
Tibia
Ligament
Figure 8.1b
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Fibrous Joints Gomphoses

• Peg-in-socket joints of teeth in alveolar sockets
• Fibrous connection is the periodontal ligament

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(c) Gomphosis
Peg in socket fibrous joint. Periodontal ligamen
t holds tooth in socket.
Socket of alveolar process
Root of tooth
Periodontal ligament
Figure 8.1c
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Cartilaginous Joints

• Bones united by cartilage
• No joint cavity
• Two types
• Synchondroses
• Symphyses

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Cartilaginous Joints Synchondroses

• A bar or plate of hyaline cartilage unites the
  bones
• All are synarthrotic

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(a) Synchondroses
Bones united by hyaline cartilage
Sternum (manubrium)
Epiphyseal plate (temporary hyaline
cartilage joint)
Joint between first rib and sternum (immovable)
Figure 8.2a
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Cartilaginous Joints Symphyses

• Hyaline cartilage covers the articulating
  surfaces and is fused to an intervening pad of
  fibrocartilage
• Strong, flexible amphiarthroses

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(b) Symphyses
Bones united by fibrocartilage
Body of vertebra
Fibrocartilaginous intervertebral disc
Hyaline cartilage
Pubic symphysis
Figure 8.2b
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Synovial Joints

• All are diarthrotic
• Include all limb joints most joints of the body

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Synovial Joints

• Distinguishing features
• Articular cartilage hyaline cartilage
• Joint (synovial) cavity small potential space

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Synovial Joints

• Distinguishing features
• 3. Articular (joint) capsule
• Outer fibrous capsule of dense irregular
  connective tissue
• Inner synovial membrane of loose connective tissue

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Synovial Joints

• Distinguishing features
• 4. Synovial fluid
• Viscous slippery filtrate of plasma hyaluronic
  acid
• Lubricates and nourishes articular cartilage

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Ligament
Joint cavity (contains synovial fluid)
Articular (hyaline) cartilage
Fibrous capsule
Articular capsule
Synovial membrane
Periosteum
Figure 8.3
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Synovial Joints

• Distinguishing features
• 5. Three possible types of reinforcing ligaments
• Capsular (intrinsic)part of the fibrous capsule
• Extracapsularoutside the capsule
• Intracapsulardeep to capsule covered by
  synovial membrane

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Synovial Joints

• Distinguishing features
• 6. Rich nerve and blood vessel supply
• Nerve fibers detect pain, monitor joint position
  and stretch
• Capillary beds produce filtrate for synovial fluid

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Synovial Joints Friction-Reducing Structures

• Bursae
• Flattened, fibrous sacs lined with synovial
  membranes
• Contain synovial fluid
• Commonly act as ball bearings where ligaments,
  muscles, skin, tendons, or bones rub together

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Coracoacromial ligament
Subacromial bursa
Humerus resting
Cavity in bursa containing synovial fluid
Bursa rolls and lessens friction.
Humerus head rolls medially as arm abducts.
Humerus moving
(b) Enlargement of (a), showing how a
bursaeliminates friction where a ligament (or
otherstructure) would rub against a bone
Figure 8.4b
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Synovial Joints Friction-Reducing Structures

• Tendon sheath
• Elongated bursa that wraps completely around a
  tendon

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Acromion of scapula
Coracoacromial ligament
Joint cavity containing synovial fluid
Subacromial bursa
Fibrous articular capsule
Hyaline cartilage
Tendon sheath
Synovial membrane
Tendon of long head of biceps brachii muscle
Fibrous capsule
Humerus
(a) Frontal section through the right shoulder
joint
Figure 8.4a
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Stabilizing Factors at Synovial Joints

• Shapes of articular surfaces (minor role)
• Ligament number and location (limited role)
• Muscle tone, which keeps tendons that cross the
  joint taut
• Extremely important in reinforcing shoulder and
  knee joints and arches of the foot

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Synovial Joints Movement

• Muscle attachments across a joint
• Originattachment to the immovable bone
• Insertionattachment to the movable bone
• Muscle contraction causes the insertion to move
  toward the origin
• Movements occur along transverse, frontal, or
  sagittal planes

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Synovial Joints Range of Motion

• Nonaxialslipping movements only
• Uniaxialmovement in one plane
• Biaxialmovement in two planes
• Multiaxialmovement in or around all three planes

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Summary of Characteristics of Body Joints

• Consult Table 8.2 for
• Joint names
• Articulating bones
• Structural classification
• Functional classification
• Movements allowed

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Table 8.2 (1 of 4)
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Table 8.2 (2 of 4)
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Table 8.2 (3 of 4)
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Table 8.2 (4 of 4)
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Movements at Synovial Joints

• Gliding
• Angular movements
• Flexion, extension, hyperextension
• Abduction, adduction
• Circumduction
• Rotation
• Medial and lateral rotation

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Movements at Synovial Joints

• 4. Special movements
• Supination, pronation
• Dorsiflexion, plantar flexion of the foot
• Inversion, eversion
• Protraction, retraction
• Elevation, depression
• Opposition

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Gliding Movements

• One flat bone surface glides or slips over
  another similar surface
• Examples
• Intercarpal joints
• Intertarsal joints
• Between articular processes of vertebrae

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Gliding
(a) Gliding movements at the wrist
Figure 8.5a
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Angular Movements

• Movements that occur along the sagittal plane
• Flexiondecreases the angle of the joint
• Extension increases the angle of the joint
• Hyperextensionexcessive extension beyond normal
  range of motion