Answers
A. FIBROUS JOINTS (SUTURE AND SYNDESMOSIS)
Suture
Name two sutures in the cranium.
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You should be aware of the two main sutures :
1. The sagittal suture which in the midline
from the top of the skull backwards. Also note the lambdoid suture at the posterior end of the sagittal suture. Together with the sagittal suture it forms an inverted letter Y. |
Do sutures allow movement between the bones?
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Sutures are immovable joints. But note that in the foetus the unossified connective tissue between bones forms a broader band and the bones are softer. Passive movement therefore does take place between bones. During birth the bones forming the sutures can be approximated and may even overlap ("override"). |
Are sutures retained throughout life?
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No. The fibrous tissue undergoes ossification and sutures are obliterated. However : There is no fixed timeline for this process and it is not a reliable method of estimating the age of a person from the fusion of sutures. Fusion of bones usually begins on the inner surface. |
Developmentally, what do sutures represent?
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Unossified areas in the skull. |
Syndesmosis
Identify syndesmoses between the shafts of the radius and ulna, and tibia and fibula. Name these two syndesmoses.
Do syndesmoses allow movement between the bones?
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Some movement is possible at syndesmoses. In most cases it is passive movement. |
Are syndesmoses retained throughout life?
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Yes! |
Should any ligament between bones be classified as a syndesmosis?
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No. Majority ligaments are accessory structures of synovial joint. However, some ligaments and membranes which are not parts of synovial joints are nowadays formally classified as syndesmoses. You need not worry about them! Just remember that the interosseous ligaments of the forearm and the leg are called the "middle joints" between the respective bones. |
B. CARTILAGENOUS JOINTS (SYNCHONDROSIS AND SYMPHYSIS)
Synchondroses
Where in the body are synchondroses found?
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Wherever there are growing bones which ossify in cartilage! |
Do synchondroses allow movement between the bones?
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No. A synchondrosis is functionally not a joint at all - it is a growth mechanism. |
Should we even consider a synchondrosis as a joint? J
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See the answer above. |
What kind of cartilage connects the bones in a synchondrosis?
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Hyaline cartilage. |
Are synchondroses retained throughout life?
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If you see the answers to the first two questions (and the next) this should be obvious. |
What is synostosis?
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At the end of growth period the last of the cartilage is replaced by bone and the "two bones" become continuous. This is called synostosis. |
Symphyses
Do symphyses allow movement between the bones?
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Some degree of movement is possible. This is due the fact that white fibrocartilage is deformable. |
What kind of cartilage connects the bones in a symphysis?
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White fibrocartilage. But note that while the white fibrocartilage is thick, each bone is covered also with a thin layer of hyaline cartilage. |
Are symphyses retained throughout life?
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Yes, that is what distinguishes them from synchondroses. |
Apart from the pubic symphysis, where else in the body are symphyses found?
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Intervertebral discs - that is, joints between bodies of vertebrae. Also between the manubrium and the body of the sternum. |
C. SYNOVIAL JOINTS
D. CLASSIFICATION OF SYNOVIAL JOINTS
Examine the atlas and axis.
How is the dens of the axis held in position?
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By a ring of bone and fibrous tissue. Three fourths of the ring are formed by the atlas, the remaining by the transverse ligament of the atlas. In the picture, the blue structure is the dens, the green band is the ligament. (The yellow circle represents the spinal cord).
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What are the possible movements between these two bones?
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Rotation. When the atlas rotates it carries the head with it. |