CH.8

Joints - articulations

Sites where two or more bones meet

Function : hold skeleton together

Provide mobility

• Structural :

  • Absence / presence of joint cavity

  • Material binding bones together

    • Fibrous : no joint cavity

    • Cartilage: no joint cavity

    • Synovial: joint cavity

• Functional :

  • Amount of movement allowed at a joint

Synarthroses : immovable

• Fibrous

Amphiarthroses: slightly moveable

Diarthroses: freely moveable joints

• Synovial joints

• More moveable = less stable

• Fibrous Joints

  • Most are synarthrosis

  • Connected by collagen fibers

  • 3 types :

    • Gomphosis

      • Teeth, peg in socket

      • Ligament holds tooth in socket

        • Periodontal ligament

    • Suture

      • Seams between cranial bones

      • Middle age: fuse and ossify

        • Synostoses

    • Syndesmosis

      • Bones connected by ligament

      • Movement depends on length of ligament (fibers)

      • Large movement at interosseous membrane :

        • Ligament Between bones connecting radius/ulna and tibia/fibula

• Cartilaginous joints

  • Connected by cartilage

  • 2 Types :

    • Synchondroses

      • United by hyaline cartilage

      • After epiphyseal plate closes

      • Synarthrosis

    • Symphyses

      • United by fibrocartilage (stronger)

      • Intervertebral disc

      • Pubic symphysis

• Synovial joints

  • Fluid filled joint cavity

  • Diarthrotic - freely moveable

  • Nearly all joints of limbs

  • 6 distinguishing features:

    • Articular cartilage - avascular

      • Hyaline cartilage cover opposite bone surfaces

    • Joint cavity

      • Space with small amount of synovial fluid

    • Synovial fluid

      • Slippery fluid in cavity

        • Primarily of water/plasma and hyaluronic acid

    • Articular capsule (two-layer)

      • Outer - fibrous layer

      • Inner- synovial membrane

    • Reinforcing ligaments

      • Capsular : thickening of fibrous layer

      • Extracapsular : extra capsule outside capsule

      • Intracapsular: deep to the capsule, covered in synovial membrane

    • Blood vessels & Nerves

      • Innervate the capsule

      • Detect pain ; most monitor joint positions and stretch

  • Some synovial joints

    • Fatty pads - knee and hip joints

      • Cushioning between fibrous layer and synovial membrane or bone

    • Articular discs (menisci)

      • Fibrocartilage

      • Seperates articular surfaces to :

        • Improve fit of bone ends

        • Stabilize joint

        • Reduce wear and tear

• Structures associated with synovial joints

  • Burase - bags of lubricant

    • Lined with synovial membrane

    • Reduce friction between a ligament and a bone

  • Elongated bursae

    • Tendon Sheats

      • Help reduce friction

• 3 factors influencing stability of synovial joint

  • Shapes of articular surfaces : minor role

    • Hip joint

  • Ligament number and location : limited role

  • Muscle tendons: most important

    • Cross a joint

    • Muscle tone keeps tendons taut (tense)

      • Reinforced shoulder and knee joints

      • Arches of foot

• Movements allowed by synovial joints

  • Muscles attach to bone at minimum 2 points

    • Origin - attaches to immovable bone

    • Insertion - attaches to movable bone

  • Muscle contraction across joints

    • Insertion moves towards origin

  • Movement along various planes

  • Range of motion

    • Nonaxial

      • Slipping movements only

    • Uniaxial

      • Movement in one plane

    • Biaxial

      • Movement in two planes

    • Multiaxial

      • Movement in all three planes

• General types of movements in synovial joints

  • Gliding

    • Repression

  • Angular movements

    • Increase/decrease angle between two bones

      • Extension, flexion, hyperextension

      • Abduction (away from midline)

      • Adduction (towards midline)

      • Circumduction (cone space)

  • Rotation

    • Medial / lateral rotation