Joints Course Materials

Joints ● ● ● Articulation between two or more bones Function: ○ Support the body ○ Allow movement ○ Protect soft organs underneath Classification: ○ Functional (degree of movement) ○ Structural (anatomical features) Functional classification 1. Synarthrosis - no movement 2. Amphiarthrosis - little movement 3. Diarthrosis - freely movable Structural classification ● Anatomical features such as: ○ Connective tissue uniting bones ○ Presence/absence of space between articulating surfaces (more space = more movement) ● All components of connective tissue → ECM, collagen, elastin in different amounts, composition, orientation in that tissue ● Elastic is not really in joints (other cavities) Type of specialised connective tissue Bony Osseous (bone) tissue binds the bones together Components Formed when 2 bones fuse together Function Immovable (synarthrosis) Location Skull → frontal bone fuses together into one Support Osteoblasts Protection Osteoclasts No evidence of separate bones Movement Osteocytes (osteoblasts surrounded by the product that they secreted) Calcium storage Long bones (epiphyseal line) ECM Fibrous Chondrocytes Two bones separated by dense regular collagenous connective tissue Collagen based 3 types: Suture More ECM 1. Suture (immovable) - Holds the joints together without the bones fusing together - Fibrous connective tissue above, below Cranial cavity (don’t want the bones to move to protect the soft organs) Gomphosis and between surfaces 2. Gomphosis ‘bolt’ (immovable) - A little bit of movement at the joint to absorb some of the pressure from biting down 3. Syndesmosis (limited movement) - Bandage that wraps the bones together - Maintain their position within the limb but still allowing some movement - Allows for a little bit of movement and weight bearing - Where the teeth are embedded into the mandible and maxilla Syndesmosis - Where the two smaller long bones of the upper and lower limbs join - Allows a little bit of movement e.g. radius can move over the ulna - E.g. the tibia malleolus can spread to absorb some weight but bones don't separate Cartilaginous PRIMARY Synarthrosis Synovial joints Two bones separated by cartilage (no space for movement) Synchondrosis (hyaline) Support Cartilaginous joints Chondrocytes trapped within the cartilage Protection Epiphyseal bones - Diaphysis and epiphysis is separated by the epiphyseal plate (block of cartilage), synchondrosis during develop until it becomes a bony joint Resists compression Lots of ECM The collagen looks like glasslike strands Creates a smooth, frictionless surface Costochondral joint - Little bit of movement but not much - Majority of movement is at the connection between the cartilage and sternum - Gives thoracic cage flexibility (respiration, CPR) SECONDARY Amphiarthrosis Symphysis (fibrocartilage) Weight bearing/support Shock absorption Chondrocyte Protection Collagen fibres Lots of ECM Rough in appearance and looks worn out Intervertebral discs - Only in the movable regions of the vertebral column - Fibres arranged in a ring shape → important for shock absorption, weight bearing - Capable of movement because of the presence of the cartilage (not bone to bone) Fibres are arranged haphazardly to resist stresses in multiple directions Pelvic bone - Shock absorption when force comes up through the lower limb → acetabulum → pelvis → absorbed in the symphysis until it's redistributed (no pain when we walk, run, jump) Synovial joint Synovial fluid - Lubrication of articular surfaces - Shock absorption - Nourishment (articular cartilage is aneural but is still a living tissue that gets nutrients through diffusion) Joint (synovial cavity) - Creates an environment for the frictionless movement of synovial joints Diarthrosis Movements: - Flexion and extension - Abduction and adduction - Rotation - Tight FC = less movement - Loose FC = more movement Ligaments (bone to bone) - Dense regular connective tissue that connects bone to bone - Strong ligaments = ↑ Articular hyaline cartilage - Covered in cartilage but the cartilage doesn’t bind them together - Avascular and aneural for protection - Fibrous capsule - The fibrous capsule is dense connective tissue and it is continuous with the periosteum (outermost layer of the bone) - Seals joint off so the synovial fluid can't get out, binds articulating bones together - Restricts movement or allow movement (based on if the joint is stable or mobile) - more movement in a particular plane but not in another - Synovial membrane - Produces the synovial fluid Elastic (not present in the joint looked at today) present in the joint looked at today) Chondrocytes Elastic fibres ECM - - - - joint stability Weak ligaments = ↓ joint stability Prohibits movements in undesirable directions (knee brace doesn’t allow sideways movement of the knee) Determines ROM around the joint May hold important structure in position Can be inside or outside the fibrous capsule ‘Bandaids that hold the bone together’ Bursae - Fluid filled ‘balloons’ - Reduce friction in that area where there is rubbing between tissue types - Provides cushioning so that the skin can move over the bone without tearing it - Overuse injury → inflammation of the bursae → pain and pressure - Found where friction between tissues happens on a daily basis Detecting and producing sound Ligaments Bursae - Areas of high stress - Between skin and bone - Between tendon and bone - Between muscle and bone Ears, epiglottis of the larynx