- Joint is the point where two or more bones meet. Joints allow different degrees of movement.
- There are many articulations or joints present in the skeleton.
- Joints are classified based upon their structure and the kinds of movements which they permit.
- Three main types of joints are
i. Immovable joints (Synarthroses)
ii. Imperfect movable joints (Amphiarthroses)
iii. Perfect movable joints (Diarthroses)
IMMOVABLE JOINTS OR FIXED JOINTS
No joint cavity, no movement possible. These are without sinovial capsule and ligaments. These joints include.
Found between skull bones, Sutures are fixed or fibrous joints, articulating bones are held together by white fibrous tissue.
Teeth in mandibles, present in premaxillary and maxillary bones.
Ethmoid bone in vomer (one bone fits into slit in another)
IMPERFECT MOVABLE JOINTS
- With or without joint cavities, permits a small amount of movement. Fibrocartilage is placed between the bones.
- These joints are also called cartilaginous joints or slightly movable joints. Sinovial capsule and ligaments also absent.
Eg. Between successive vertebrae,
Between bones of the pubic symphysis,
Sacro-iliac joint in frog.
PERFECT MOVABLE JOINTS
- Movable joints are called synovial joints.
- Synovial joint has a synovial or joint cavity, a space between articulating bones.
- Articular cartilage covers the surface of articulating bones.
- Articular cartilage of synovial joint is hyaline cartilage.
- Synovial joints are surrounded by a 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 synovia) fluid.
CLASSIFICATION OF SYNOVIAL JOINTS
i. Synovial joints are furtherclassified according to the movements they permit. The main types are ball and socket joints, hinge joints, gliding joints, pivot joints, saddle joints, ellipsoid joints, etc.
ii. Ball and socket joint is a type of sinovial joint which allows movement in all directions. In this joint one articular face is in the form of a socket and the other is in the form of a spherical head. The head of bone can rotate freely inthe socket of the other allowing free movement. Shoulder and hip joints are of this type.
iii. Hinge joint is a type of sinovial joint which allows movement in one plane. Elbow joint, knee joint and joints between phallanges of digits are of this type.
vi. Pivot joint is a sinovial joint in which one of the two bones is fixed and the other rotates over it. Ex: Head joint and the joint between radius and ulna.
v. Gliding joint is a sinovial joint in which the end of one bone glides across the surface of a part of the other bone. The joints of wrist, ankle, sternum, clavicle and that of zygapophyses of vertebrae are of this type.
vi. Saddle joints between carpals and radius, permit movements in two planes at right angles to each other.
vii. Ellipsoid joints permit movements of articulating bones around two axes.
viii. Ellipsoid joints are formed between the toe bones and some bones in the sole of foot.
Movements are produced at joints by contractions of skeletal muscles inserted into the articulating bones.