There are many articulations or joints present in the skeleton. Joint or articulations is a point of contact between bones. Joints are classified based upon their structure and the kinds of movements which they permit. Three main types of joints are -
(1) Immovable joints (Synarthroses) : No joint cavity, no movement possible. These joints include -
(i) Sutures : Found between skull bones, sutures are fixed or fibrous joints, articulating bones are held together by white fibrous tissue.
(ii) Gomphoses : It is a type of fibrous joint in which cone shaped peg fits soket. Teeth in mandibles, and maxillary bones.
(iii) Syndesmosis : It is type of fibrous joint with more fibrous tissue than sutures. e.g., distal articulation between Tibia and fibula.
(2) Imperfect joints (Amphiarthroses) slightly movable : Joints in which syanovial cavity is absent. Permit a small amount of movement. Fibrocartilage is placed between the bones. These are cartilaginous joints e.g., Pubic symphysis, between bodies of the vertebrae, between the manubrium and the body of sternum, sacroilliac joint in frog.
(3) Perfect joints (Diarthroses) freely movable : Syanovial cavity and ligaments are present. These are typical joints having articulate surface and syanovial capsule. Syanovial fluid act as a grease in the joint e.g., Joints of elbow, ankle, wrist, hip, knee. Articular cartilage covers the surface of articular bones. Articular cartilage of synovial joint is hyaline cartilage. Synovial joints are surrounded by tubular articular capsule. The articular capsule consists of two layers, outer fibrous capsule and inner synovial membrane. The synovial membrane secretes synovial fluid which lubricates and provides nourishment to articular cartilage. In old age stiffness of joints is due to the decrease in synovial fluid.
(i) Ball and socket joint : Also known as enarthroses. Ball of one bone articulate in socket of another bone. e.g., head of humerus and glenoid cavity of pectoral girdle, femur and acetabulum of pelvic girdle, joint between incus and stapes.
(ii) Hinge joint : Also known as gingulum. Movement is possible in one direction only. e.g., Joint of malleus and incus, knee joint, elbow joint, articulation joint of lower jaw, joint of phalanges of digits.
(iii) Pivot joint : Also known as rotatoria and helps in turning movement. One bone is fixed and second articulate. e.g., Atlas and axial of skull rotate with axis vertebra also known as atlanto axial joint.
(iv) Gliding joint : Also known as arthrodial, limited movement in all more...