Joints

Articulations Articulations (joints) are places where two or more separate bones in the body meet Bones will endure extreme friction if they rub against each other, therefore all joints have at least one of these two traits: – Immobile – Padded with other tissues such as cartilage

Structural Classification of Joints Based on material binding bones together and whether or not a joint cavity is present Three structural classifications: Fibrous joint Cartilaginous joint Synovial joint The only movable one

Functional Classification of Joints Based on amount of movement allowed by the joint Three functional classifications: Synarthrosis—immovable Amphiarthrosis—slightly movable Diarthrosis—freely movable

Fibrous Joint A fibrous joint is always completely immobile (synarthrosis) Composed of dense fibrous connective tissue Major example are the sutures in the skull Dense fibrous connective tissue Suture line (a) Suture Joint held together with very short, interconnecting fibers, and bone edges interlock. Found only in the skull.

Cartilaginous Joint A cartilaginous joint is composed of hyaline cartilage attached to both bones and is often a synarthrosis Sometimes a disc of fibrocartilage sits between the articular cartilages of the bones – This is called a symphysis – This type of joint is an amphiarthrosis Fibrocartilaginous intervertebral disc Pubic symphysis Body of vertebra Hyaline cartilage (b) Symphyses Bones united by fibrocartilage

Cartilaginous Wear Remember that cartilage is ossified to bone over time – This continues slowly in adulthood! Many cartilaginous joints becomes less flexible over time – This includes the cartilage of the ribcage and the pubic symphysis

Synovial Joint Any joint that is designed to move more than 2 millimeters is a synovial joint – This includes knee, elbow, shoulder, jaw, etc. Each end of the bone is covered in cartilage, the space between the bones is filled with synovial fluid, and the entire joint is covered in the fibrous capsule

Synovial Joint Structure The fibrous capsule protects the joint from the outside The synovial fluid prevents the cartilage or bone from ever grinding against each other Additionally, ligaments hold the bones together – Ligaments are prevented from wearing down bone or cartilage by fluid-filled membrane sacs called bursae (sing. bursa)

Anatomy of Major Joints

Basic Joint Movements Synovial joints have many types of joints and movements – Flexion/Extension – Abduction/Adduction – Circumduction – Rotation These will be covered in lab as well – There are many more specialized movements not covered here

Flexion/Extension Movement in the sagittal plane – Decreased angle = flexion – Increased angle = extension – Beyond straight = hyperextension Vertebral joints (amphiarthroses) may collectively perform flexion/extension as well

Adduction/Abduction Movement in the frontal plane – Away from body = abduction – Adding to body = adduction Available in many appendicular joints

Circumduction and Rotation Circumduction is to inscribe a cone (simultaneous use of flexion/extension and adduction/abduction) – What joints can perform circumduction? Rotation is to rotate in place – What joints can perform rotation?

Joint Inflammation A joint may become inflamed with age – Referred to as arthritis – Rheumatoid arthritis is an immune reaction to the joint – Osteoarthritis is a wearing down of the cartilage on a joint and the subsequent thickening of the bone due to friction If a bursa becomes inflamed it is called bursitis

That’s all folks! Have an excellent weekend! Don’t forget to take the online quiz! Next week: Electrical activity, then muscles!