Question

Discuss three articulations in the human body. Talk about their classifications. Please include references

Answer 1

Ans:

A joint or articulation is a location at which two bones come into contact. They are constructed to allow for different degrees of movement and provide mechanical support. There are three main types of articulations or joints in the human body based on structures: Fibrous, Cartilaginous and Synovial.

Structural Classification: Structurally, joints are classified as:

(1) Fibrous Joints: Fibrous joints are connected by tight and inflexible layers of dense connective tissue, consisting mainly of collagen fibers. These are fixed joints where bones are united by a layer of white fibrous tissues. Such immovable joints are also called as synarthroses. The skull bones are connected by fibrous joints called sutures.

Examples of fibrous joints are: (i) Cranial sutures: joining the bones of the cranium, (ii) Gomphoses: the joints between the roots of the teeth and their sockets and in maxilla and mandible.

(2) Cartilaginous Joints: Cartilaginous joints are connected entirely by cartilage. They allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. There are two types of cartilaginous joints: Synchondroses and Symphyses. In synchondroses, the bones are joined by hyaline cartilage and in symphyses, the bones are joined by fibrocartilage.

Examples of cartilaginous joints are: (i) Intervertebral joints - Symphyses (bones are joined by fibrocartilage), (ii) Epiphyseal plate of a child's long bone - Synchondroses (bones are joined by hyaline cartilage).

(3) Synovial Joints: Synovial joints, also known as diarthrosis joint, joins bones with a fibrous joint capsule. There are seven types of synovial joints: (i) Plane joints (gliding joint) (ii) Hinge joints, (iii) Pivot joints, (iv) Condyloid joints, (v) Saddle joints, (vi) Ball and socket joints. (vii) Compound or bicondyloid joints.

Examples of synovial joints are: (i) Joints between the axis and atlas, Joint between forearm bones and wrist - Pivot joints, (ii) Hip joints - Ball and Socket joints, (iii) Elbow, Interphalangeal and Joint between talus and tibia/ fibula - Hinge joints.

Functional Classification: Functionally, Joints can be classified as:

(1) Synarthrosis Joints: Synarthroses are joints with very little mobility and allow no movement. There are fusion of two bones, at a point that practically becomes one bone. In humans, the plates of the cranium are initially seperated from each other and later on fuse together as child grows into adult.

(2) Amphiarthroses Joints: These are slightly movable joints which allow a little movement. The joints at the surface of two bone are covered with a hyaline cartilage and are joined by strands of fibrocartilage. Most of the amphiarthroses joints are cartilaginous.

(3) Diarthroses Joints: Also called as synovial joints. Diarthroses (freely movable articulations) includes the greater number of the joints in the body. In this type of joint, bony surfaces are covered with articular cartilage and connected by ligaments lined by synovial membrane. The joint may be divided completely or incompletely by an articular disk.