Synovial Joint And Its Structures

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Articulations or Joints are specialized anatomical structures at

which the ends of certain bones are joined or the borders of other bones

are juxtaposed. These osseous junctions are secured by ligaments,

fibrous capsule and other binding tissues which restrict movements or

permit varying degrees of movements. Joints vary widely in their

structure, frequently presenting unique morphological features, adapted to

specific functional requirements.

JOINT CLASSIFICATION:

Depending on the morphological characteristics of the joints, they

are classified into,

1. Fibrous Joints – Many of which are immovable and are

united by fibrous tissue (synarthroses).

2. Cartilaginous Joints – Slightly movable, the union between

the bones occurs via cartilage

(amphiarthroses).

3. Synovial Joints – Freely movable (diarthroses)

SYNOVIAL JOINTS:

Synovial Joints are highly evolved articulations which permit free

movements. Because the human lower limbs are concerned with

locomotion and the upper limbs provide a great versatility of movements,

it is not surprising that most of the joints are of the synovial type. The

integrity of a synovial joint results from its ligaments and capsule which

bind the articulation externally and to some extent from the surrounding

muscles. The contiguous bony surfaces are covered with hyaline

cartilage and the joint cavity is surrounded by a fibrous capsule, the inner

surface of which is lined by a synovial layer containing cells that are

thought to secrete the viscous lubricating synovial fluid.

STRUCTURES:

1. Articular Cartilage: Firmly adherent to the articular surfaces of

majority of bones. They are neither innervated nor supplied with

blood vessels.

2. Ligaments: are composed mainly of bundles of collagenous fibres.

They are pliant and flexible to allow perfect freedom of movement.

3. Articular Capsule: Forms a complete envelope for a freely

movable joint and consists of external fibrous layer and internal

synovial layer. The fibrous layer gets attached to the periosteum

along the entire circumferance of the articular end of each bone.

Its flexibility permits movements, yet its strength protects joint

from dislocation.

4. Synovial Membrane: Covers the inner surface of the fibrous

capsule, forming a closed sac called the synovial cavity. It is

composed of loose connective tissue and it has a free surface of

finger like projection called the Synovial Villi. The synovial cavity

contains only enough synovial fluid to moisten and lubricate the

synovial surfaces, but in an injured or inflammed joint, the fluid

may accumulate in painful amounts.

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