CHARACTERSTICS OF SYNOVIAL JOINT .

CHARACTERSTICS OF SYNOVIAL JOINT .

All synovial joints have certain characterstics in common.

1. Articular Or Hylaine Cartilage :

2. Capsule Or Capsular Ligament

3. Synovial Membrane

4. Other Intracapsular Structures

5. Extracapsular Structures

6. Nerve And Blood Supply .

v ARTICULAR OR HYLAINE CARTILAGE:

Ø The parts of the bones which are in contact are always covered with hyaline cartilage.

Ø It provides a smooth articular surface and is strong enough to absorb compression forces and bear the weight of the body.

Ø The cartilage lining , which is up to 7 mm thick in young people, becomes thinner and less compressible with age .

Ø This leads to increasing stress on other structures in the joint.

Ø Cartilage has no blood supply and receives its nourishment from synovial fluid.

v CAPSULE OR CAPSULAR LIGAMENT:

o The joint is surrounded and enclosed by a sleeve of fibrous tissue which holds the bones together.

o It is sufficiently loose to allow freedom of movement but strong enough to protect it from injury.

v SYNOVIAL MENBRANE :

This is composed of epithelial cells and is found.

1. Lining the capsule.

2. Covering those parts of the bones within the joint not covered by articular cartilage.

3. Covering all intracapsular structures that do not bear weight.

v SYNOVIAL FLUID :

· This is a thick sticky fluid, of egg-white consistency , secreted by synovial membranes into the synovial cavity.

· Little sacs of synovial fluid or bursae are present in some joints, e.g. the knee.

· They act as cushions to prevent friction between a bone and a ligament or tendon, or skin where a bone in a joint is near the surface.

FUNCTIONS:

1. Synovial fluid provides nutrients for the structures within the joint cavity .

2. Contains phagocytes , which remove microbes and cellular debris.

3. Act as a lubricant

4. Maintains joint stability

5. Prevents the ends of the bones from being separated , as does a little water between two glass surfaces.

v OTHER INTRACAPSULAR STRUCTURES:

· Some joints have structures within the capsule , but outside the synovial membrane ,which assist in maintenance of stability , e.g . fat pads and menisci in the knee joint.

· When these structures do not bear weight they are covered by synovial membrane.

v EXTRACAPSULAR STRUCTURES:

Ø LIGAMENTS that blend with the capsule provide additional stability at most joints.

Ø MUSCLES or their tendons also provide stability and stretch across the joints they move .

Ø When the muscle contracts it shortens , pulling one bone towards the other.

v NERVE AND BLOOD SUPPLY :

Nerves and blood vessels crossing a joint usually supply the capsule and the muscles that move it.

MOVEMENTS AT SYNOVIAL JOINTS.

movements at any given joint depends on various factors, such as the tightness of the ligaments holding the joint together ,how well the bones fit and the presence or absence of intracapsular structures.