A closer look at synovial joints

Question 1

What are the different types of joints?

Answer 1

1. Fixed/fibrous joints
2. Cartilaginous joints
3. Synovial joints

Question 2

What are fibrous joints?

Answer 2

They have no joint cavity and the bones are held together by fibrous tissue. This allows no movement whatsoever.

Question 3

What are cartilaginous joints?

Answer 3

These have no joint cavity, but there is cartilage between the bones of the joint. They allow limited movement and are most common in the vertebral column.

Question 4

What are synovial joints?

Answer 4

They have a fluid filled cavity surrounded by an articular capsule. The bones articulating are covered in hyaline cartilage. They are freely mobile joints.

Question 5

What are the four general features of synovial joints?

Answer 5

1. Hyaline cartilage - covers the ends of the bones forming the joint.
2. Fibrous articular capsule - the joint surfaces are enclosed by a sleeve of fibrous connective tissue lined with a Smooth membrane called the the synovial membrane.
3. Joint cavity - the articular capsule encloses the joint cavity, which contains lubricating synovial fluid.
4. Reinforcing ligaments - the fibrous capsule is reinforced by strong bands called ligaments, which join bone to bone and hence make the joint more stable.

Question 6

Where are bursae, menisci and tendon sheaths found?

Answer 6

They are often found near where tendons (muscle to bone) are in contact with the bone. They are mostly apparent in the knee joint.

Question 7

What are bursae?

Answer 7

They are fluid filled sacs between the tendon and the bone and help to reduce friction.

Question 8

What are menisci?

Answer 8

Menisci or semi lunar (half-moon shaped) cartilage act as shock absorbers.

Question 9

The structure and function of articular/hyaline cartilage:

Answer 9

Structure - glassy smooth cartilage that is spongy, covering the ends of the bones.

Question 10

The function of articular/hyaline cartilage:

Answer 10

Function - prevents friction, absorbs compression.

Question 11

Structure of two layered joint capsules:

Answer 11

The outer layer - the fibrous capsule - is tough and fibrous. The inner layer - the synovial membrane - covers all the internal joint surfaces except the articular cartilage.

Question 12

Function of two layer joint capsules:

Answer 12

Reduces friction between the articular cartilage, nourishes the articular cartilage, rids the joint of debris.

Question 13

What is a ligament?

Answer 13

A band of strong fibrous tissue that connects one bone to another.

Question 14

Structure of bursa:

Answer 14

Flattened fibrous sacs lined with a synovial membrane containing a thin film of synovial fluid.

Question 15

Function of bursa:

Answer 15

Prevents friction at sites where muscles, ligaments, tendons or bones may rub together.

Question 16

Structure of meniscus:

Answer 16

A wedge of white fibrocartilage that improves the fit between adjacent bond ends.

Question 17

Function of meniscus:

Answer 17

Increases joint stability and reduces friction between joints.

Question 18

What is the function of pads of fat?

Answer 18

Fatty pads are located between capsule, bone or muscle, increasing joint stability and reduces friction between joint surfaces.

Question 19

Name the different types of synovial joints:

Answer 19

Plane/gliding, hinge, pivot, condyloid, saddle, ball and socket.

Question 20

What is a ball and socket joint?

Answer 20

• Consists of the spherical head of one bone that fits into a round socket of another bone
• They are multiracial joints allowing movements in all axes

Question 21

What is a saddle joint?

Answer 21

• Each articular surface has both convex and concave areas like a saddle
• These are biaxial joints, moving side to side and back and forth, but the bone cannot move about its long axis

Question 22

What is a condyloid joint?

Answer 22

• The egg-shaped surface of one bone fits into an oval concavity of another bone, with bone of these surfaces being oval
• They move from side to side and back and forth, but the bone cannot move about its long axis
• Movement occurs around the two axes hence these joints are bixial

Question 23

What is a pivot joint?

Answer 23

• The rounded end of one bone fits into a sleeve or ring of another bone
• Because the rotating bone can only rotate around its long axis, pivot joints are also uniaxial

Question 24

What is a hinge joint?

Answer 24

• The cylindrical end of one bone fits into the trough shaped surface of another bone
• Angular movement is allowed in just one plane, like a mechanical hinge

Question 25

What is a plane/gliding joint?

Answer 25

• The articular surfaces are essentially flat and only short slipping or gliding movements are allowed
• The movement of the plane joints are non axial, that is gliding does not involve any rotation around an axis