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

fibrousconnectivetissue

Sutureline

(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

Fibrocartilaginousintervertebraldisc

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!