Joints of Endoskeleton:
Bones are articulated with one another by joints. In movable parts of body, these joints act as fulcra on which the bones move as levers to bring about the desired movements. All joints may be classified into the following categories:
- Movable joints (diarthroses)
- Immovable joints (synarthroses)
Movable joints are classified into the following categories:
1. Perfect Joints:
In perfect joints the ends of articulating bones are covered with a thin cap of hyaline articular cartilage. The entire joint is enclosed within a tough synovial capsule. The wall of the capsule is composed of an outer dense fibrous layer and less dense, more cellular inner synovial layer. The cavity of the capsule is called synovial cavity and is filled with a sticky and lubricating synovial fluid. Perfect joint permits considerable movement of articulating bones without friction. Such joints are further reinforced by strong and elastic ligaments outside the synovial capsule. Their ligaments help in bringing the articulating bones back to their normal positions after movement. The perfect joints are of the following types:
i. Ball and socket joints (enarthroses)-
In such a joint, the ball-like end or ‘head’ of one bone fits into a socket or concavity of the other. The bone with the ball-like end can be freely rotated around. Examples of ball and socket joints include articulation of humerus bones in the glenoid cavities of pectoral girdle at shoulders and that of femur bones in the acetabula of pelvic girdle in pelvis.
ii. The hinge joints (ginglymi)-
In this case, a protuberance at the end of one bone fits into a corresponding depression of the other in such a manner that the bone with protuberance can swing like a door on its hinges only in one direction. Examples of hinge joints include knee and elbow joints and between the phalanges of digits.
iii. Pivotal or Rotary joints (rotatoria)-
In such a joint, one of the bones is fixed and bears a peg-like projection or the pivot. The other fitting over the pivot by a concavity freely rotates around. Example of pivotal joint is the first vertebra (atlas), carrying the skull, rotates freely on the peg-like odontoid process of the second vertebra (axis).
iv. The saddle joints-
These are like ball and socket joints, but both the ball and socket are poorly developed. Hence, the ball-bearing bones can be rotated around, but not very efficiently. Examples of saddle joints include metacarpal and carpal of thumb.
v. The gliding joints (arthrodia)-
In these, the articulating bones can slide upon one another at the joint, but movement is naturally restricted. Examples of gliding joints include the joints between the zygapophyses of successive vertebrae and that between the radio-ulna and carpals.
2. Imperfect Joints:
Ligaments and the synovial capsule are absent in such joints. Hence, the cartilage-tipped ends of the bones articulate directly with one another. Such joints allow little movement of articulating bones. The pubic symphysis in the pelvic girdle and between the vertebrae is example of such a joint.
Immovable joints include:
1. Sutures, which are the lines of junction between skull bones. Sutures are zigzag lines in which the serrated margins of articulating bones are interlocked.
2. Gomphoses in which a bony projection on one bone fits into a socket of the other as in the case of teeth in mandibles, premaxillary and maxillary bones.
3. Shindylases in which one bone fits into a slit in another as in the articulation of ethmoid bone with the vomer.
He has done his graduation with Mathematics Honors from Calcutta University in 2008.He has completed the final semester of MCA in Feb'2013 and developed an eLearning website in ASP.NET with C# as the major project of the MCA curriculum.He has worked as a Project Trainee in NIVT, Kolkata from Aug'2012 to Jan'2013.read more
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