(i) sockets and between skull bones. (ii)

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(i) Fibrous joints or immovable or fixed joints. (Synarthroses) (ii) Cartilaginous joints. (Amphiarthroses) (iii) Synovial joints. (Diarthroses)

(i) Fibrous joints:

These joints are immovable or fixed joints. Joints do not show any movement due to the presence of strong and tough white cartilaginous fibres, E.g., joints in tooth sockets and between skull bones.

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(ii) Cartilaginous joints:

They are slightly movable joints.

Discs of white fibro cartilage, strong but more elastic and compressible than the white fibrous tissue, hold the bones together at the joints between the bodies of the vertebrae, at the symphysis pubis, and between the sternum and ribs. The bones make some movements at such joints through compression of the discs of the cartilage.

(iii) Synovial joints:

These joints are perfect joints and allow free movements in one or more directions. Synovial joints are of different types depending upon the nature of articulation and degree of movement. Bones ends bear synovial membranes and enclose a cushion of synovial fluid. Synovial fluid lubricates the joints to allow nearly frictionless movement of bones on each other and nourishes the structures participating in the joint. It also serves to keep the bones held together like a film of water between two glass plates does.

(1) Synovial cavity: i. Contain mucin, a lubricant for joint surfaces. ii. Reduce friction between joint surfaces. iii.

Allow movements of nutrients and respiratory gases. (2) Hyaline cartilage: i. Contains no blood vessels or nerves.

Ii. Reduce friction between bones during movement. iii. Because of its elastic property, it also acts as shock absorber. (3) Fibrous capsule: i. Formed by number of ligaments.

ii. Arrangement in such a way as to cope effectively with the particular stresses suffered by the joint. (4) Synovial membrane: i. Secretes synovial fluid (a clear sticky fluid) into the synovial cavity.

ii. Act as water proof seal preventing escape of synovial fluid. iii. Allow movement of nutrients and respiratory gases. Synovial joints are of the following types: (a) Ball and socket joints (= enarthroses): The ‘head’ of one bone fitting with the ‘socket’ of the other bone and allowing free movement in all planes. E.

g. shoulder joint and hip joint. (b) Hinge joints (= ginglymi): The perfect joints which allow the movements only in a single plane. In this articular end of one bone is deeper convex and that of other is deeper concave. E.g. elbow joint and knee joint.

(c) Pivot joints (= rotary joints or rotaria): One of the two bones is fixed in its place and bears a peg like process over which rotates the other bone. E.g. atlas along with the skull rotating over the odontoid process of axis vertebra in mammals and upper ends of radius and ulna.

(d) Saddle joints: Similar to ball and socket joints but both ball and socket are poorly developed and movements are comparatively less free. It allows the bone with convex head to move in much direction. E.g. the joint between the metacarpal of thumb with the carpals below. (e) Gliding joints: The joints which permit sliding of the articulating bones on each other. E.

g. joint between radio-ulna and carpals, between the zygapophyses of successive vertebrae, between sternum and clavicle. (f) Angular (or ellipsoid or condyloid) joints: These joints allow the movements in two directions, i.

e., side to side and back and forth. E.g., wrist joints and metacarpopharyngeal joints.


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