Joints Classification

• Functional Classification of Joints


  the functional classification of joints = based on the amount of movement allowed at the joint

  synarthroses = immovable joints

  amphiarthroses = slightly movable joints

  diarthroses = freely movable joints
• Location of Synarthroses, Amphiarthroses, Diarthroses


  (diarthroses) freely movable joints predominate in the appendicular skeleton (limbs)

  immovable joints (synarthroses) + slightly movable joints (ampiarthroses) r largely restricted to the axial skeleton

  this localisation of functional joint types makes sense cos the less movable the joint, the more stable it is likely to be
• Fibrous Joints


  in fibrous joints, the bones r joined by the collagen fibres of connective tissue

  no joint cavity is present

  the amount of movement allowed depeds on the length of the connective tissue fibres

  most fibrous joints r immovable, altho a few r slightly movable
• 3 Types of Fribrous Joints


  sutures

  syndesmoses

  gomphoses
• Fibrous Joints - Sutures 


  occur only between bones of the skull

  the wavy articulating bone edges interlock + the junction is completely filled by minimal amount of v short connective tissue fibres that r continous w the periosteum
• Fibrous Joints - Structure of Sutures


  the junction that is filled in v short connective tissue fibres results in nearly rigid splices that knit the bones together, yet allow the skull to expand as the brain grows during youth
• Fibrous Joints - Ossification of Sutures


  during middle age, the fibrous tissue ossifies + the skull bones fuse into a single unit

  at this stage, the closed sutures = synostoses

  cos movement of the cranial bones would damage the brain, the immovable nature of sutures is a protective adaptation
• Fibrous Joints - Syndesmoses


  in syndesmoses, the bones r connected exclusively by ligaments, cords or bands of fibrous joints

  the amount of movement allowed at a syndesmosis depends on the length of the connecting fibres

  the connecting fibres r longer than those in sutures, but vary in length
• Fibrous Joints - Syndesmoses' Length of Connecting Fibres


  if the fibres r short as in the ligament connecting the distal ends of the tibia + fibula, lil or no movement is allowed

  if the fibres r long as in the ligament-like interosseous membrane connecting the radius + ulna, a large amount of movement is possible
• Fibrous Joints - Gomphoses


  a gomphosis = a peg-in-socket joint

  the only example is the articulation of a tooth w its bony alveolar socket

  the fibrous connection in this case = short periodontal ligament
• Cartilaginous Joints


  in cartilaginous joints, the articulating bones r united by cartilage

  like fibrous joints, they lack a joint cavity + r not highly movable

  the types of cartilaginous joints:

  synchondroses + symphyses
• Cartilagionus Joints - Synchondroses

  a bar/plate of hyaline cartilage unites the bones at a synchrondrosis

  virtually all synchondroses r synarthrotic (immovable)

  e.g. the immovable joint beween the costal cartilage of the 1st rib + the manubrium

  
• Cartilagionus Joints - Symphyses

  symphysis = joint where fibrocartilage unites the bones

  = amphiarthrotic joints designed for strength w flexibility

  since fibrocartilage is compressible + resilient, it act as a shock absorber + permits a limited amount of movement at the joint

  even tho fibrocartilage is the main element of a symphysis, hyaline cartilage is also present in the form of articular cartilages on the bony surfaces

  e.g. intervertebral joints

  
• Synovial Joints


  synovial joints r those in which the articulating bones r separated by a fluid-containing joint cavity

  this arrangement permits substantial freedom of movement

  = freely movable diarthroses

  nearly all joints of the limbs r synovial
• Synovial Joints - Articular Cartilage

  articular cartilage = glassy-smooth hyaline cartilage covers the opposing bone surfaces

  these thin but spongy cushions absrob compression placed on the joint + thereby keep the bone ends from being crushed
• Synovial Joints - Joint Articular Cavity

  the joint cavity is a feature that is unique to synovial joints

  it contiains a small amount of synovial fluid

  the cavity is a potential space cos it is normally almost nonexistent but can expand if fluid accumalates during inflammation
• Synovial Joints - Articular Capsule

  the joint cavity is enclosed by a 2 layered articular capsule

  the tough external fibrous layer = dense irregular connective tissue that's continous w the periostea of the articulating bones

  = strengthens the joints so that the bones r not pulled apart

  inner layer = synovial membrane = loose connective tissue

  besides lining the fibrous layer internally, it covers all internal joint surfaces that r not hyaline cartilage

  function of synovial membrane = to make synovial fluid
• Synovial Joints - Synovial Fluid

  synovial fluid = small amount of slippery fluid that occupies all free spaces w in the joint capsule

  this fluid is derived largely by filtration from blood flowing thru the capillaries in the synovial membrane

  also found w in the articular cartilages, providing a slipper, weight-bearing film that reduces friction between the cartilages

  w out this lubricant, rubbing would wear away joint surfaces + excessive friction woud overheat + destroy the joint tissues
• Synovial Joints - Reinforcing Ligaments

  synovial joints r reinforced + strengthened by a no of bandlike ligaments

  most often, these r capsular ligaments, which r thickened parts of the fibrous layer
• Synovial Joints - Nerve Supply

  synovial joints r richly supplied w sensory nerve fibres that inervate the capsule

  some of these fibres detect pain = awareness of joint injury

  monitoring joint stretch is one of the several ways the nervous system senses our posture + body movements
• Synovial Joints - Blood Supply

  richly supplied w blood vessels, most of which supply the synovial membrane

  there, extensive capillary beds produce the blood filtrate that is the basis of synovial fluid
• Synovial Joints - Bursae & Tendon Sheaths

  bursae + tendon sheaths r not strictly part of synovial joints, but theyr ro ften found closely associated w in them

  essentially bags of lubricant, they act as ball bearings to reduce friction between adjacent structures during joint activity
• Synovial Joints - Bursae

  bursae = flattened fibrous sacs lined w synovial membrane + containing a thin filament of synovial fluid

  they occur where ligaments, muscles, skin, tendons or bones rub together
• Synovial Joints - Tendon Sheaths

  tendon sheath = elongated bursa that wraps completely around a tendon subjected to friction

  they r common where several tendons r crowded together w in narrow canal - e.g. in the wrist