What are Joints?

A joint is the point where two or more bones are connected. Joints hold the bones together and help in movement of the skeletal system in different directions. It is also called an articular surface. These are present to allow different types of movements. For example, the connection between a tooth and the jawbone is known as a joint. The rib cage is also a type of joint which provides protection to heart, lungs, liver, and spleen.

How are Joints attached to Bones?

Bones that are close to other  bones are attached to each other by long fibrous straps called ligaments. Ligaments are present near the knee joints, elbow joints and shoulder joints and other joints. Cartilage is a flexible, rubbery substances in joints, which provides support and protection to bones against injury. It also provides cushioning to the bones.

Tendons are tough connective tissues which connect bone to muscles. These muscles control the movement of the joints. Human body contains 206 bones, which develop before the birth of the fetus. During fetal development, the skeleton forms first. Initially, it is made up of flexible cartilage, which undergoes ossification within a few weeks. Osteoblasts, the bone forming cells are active in children and young people, which promote the growth of the bones. Osteoblasts are also important and involved in the repair of fractures.

Note: From head to toes, bones provide support and shape to the body.

Different Types of Joints

A joint is a point where two or more bones meet. There are three types of joints:

• Fibrous joints which do not show any movement
• Cartilaginous joints which are partially movable, and
• Synovial joint which are freely movable and thus are also called movable joints.

Synovial joint

Synovial joint is also known as diarthrosis. It is composed of a fibrous joint capsule which is filled with synovial fluid. It mainly connects the fibrous joint capsule with the bones or cartilage. A synovial joint is made up of cartilage which is a smooth material that covers the surface of the bones. Example, knee and shoulder joints. Synovial joints are of six types which includes hinge joint (allow movement in only one direction, example, elbow and knee joint), pivot joint (also known as rotatory joint, example joint between ulna and radius), ball and socket joints (allow movement in all direction, example shoulder joint), saddle joint (does not allow rotation but provide back and forth; and side to side movement, example joint at the base of the thumb), and gliding joints (example wrist), condyloid joint (do not allow rotation movement, example joints in the jaw).

Note: These synovial joint cavities are filled with clear fluid.

Cartilaginous Joints

In the cartilaginous joints, the bones are held together by cartilages. There are two types of cartilage: hyaline cartilage (glass-like translucent cartilage) and fibrocartilage (mainly composed of collagen).

Fibrous joints

Fibrous joints are fixed and are unable to move (immovable). Theimmovable joints includesutures, gomphosis, syndesmosis.

Note: Cartilage is a tissue which covers the surface of the bone at the joint.

Synovial membrane is connective tissue which lines the inner surface of the synovial joint capsule. Synovial membrane secretes a sticky fluid. Joints hold the skeleton together and provide support for the movement.

Joints help in the Movement of Bones in Different Directions

There are different types of joints, some joints do not show any type of movement, for example, skull. The bones of skull are joined together by sutures and are referred to as synarthrodial joints or immovable joints.

Some joints exhibit movement in different directions. They are of different types:

• Ball and socket joints are present in shoulder and hip region and provide rotating, backward, and forward movements to the bones.
• Hinge joints are present in the fingers, elbows, knees and toes.It results in bending movements.
• Pivot joint are the neck joints which provide rotating movement.
• Ellipsoidal joints are the wrist joint which allow bone movement in all direction.

Note: These joints are coming under the mobile joints.

The stern costal joints

Stern costal joints connects the true rib’s costal region to the sternum. It is a type of synovial joint which is also known as stern chondral joints.

Bones in babies

Babies after birth have approximately 300 bones. Some of these bones are fused during the growth and result in 206 bones in adults. Out of 206 bones, 80 are in axial skeleton and 126 in appendicular skeletal.

What Type of Joints is in Leg?

Hinge joint is present in the leg. It consists of two articulations. The first between femur and tibia, the second between femur and patella.

What are the Three Major Leg Bones?

The leg bones are composed of the thigh-bone(femur), the shin-bone(tibia), and the fibula present below the knee cap.

What are the Strongest and Smallest Joints in the Body?

The longest and strongest joint in the body is the hip joint. It is surrounded by muscles and ligaments.

Stapes is the smallest bone in the body, also known as stirrup.

Which Joints are in the Vertebral Region?

The ribs are connected to the vertebral column by costovertebral joints. It is a synovial joint. It forms the synovial planar joint.

Where are the Axillary Joints Located?

The region below the shoulder joint which connects the arm to the shoulder is called the axillary region. This region contains two types of joints: the shoulder joints and the acromioclavicular joint.

What are the Functions of the Joint?

Joints hold the skeleton together, provide support and help in the movement of the body.

• Joint provide mobility to different parts of the body or skeletal system and
• Certain joints provide protection to the internal organs which are vital for humans.

Content and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, and research especially for

• B.Sc. (Bachelor of science) in zoology.
• B.Sc. in General physiology.
• M.Sc. (Master of science) in Human physiology.
• Masters in anatomy and physiology.

Related Concepts

• Movement of different body parts
• Skeletal system

Practice Problem

• What is abduction adduction in joints?

Solution: In humans, both abduction and adduction are the movements of the synovial joints. Abduction is the movement away from the midline of the body. Adduction is the movement towards the midline of the body. Extension, flexion and rotations are also movements of the synovial joints in the human skeletal system.