Did you know that an adult human has \(206\) bones in the body? How are these bones attached to each other? Have we ever thought about how we can walk? What helps us in lifting objects? Joints make all these movements possible. We cannot imagine our daily life without Joints.

In the absence of joints, our body will become stiff, and we will not be able to do any activity. Joints produce flexibility to the skeleton by connecting the bones. All joints have a different way of functioning, and they are involved in other forms of movement. In this article, we will discuss in detail about Joints, Definition, Classification, Functions, etc. Continue reading to know more.

Definition of Joints

A Joint or Articulation is the point where two or more bones or a bone and a cartilage are attached to the body.

Joints are involved for the purpose of allowing body parts to move. Joints hold our bones together and help the skeletal system to complete its functions. The three main joints in the body are fibrous, cartilaginous, and synovial.

Classification of Joints Based on Structure

Joints are classified in two ways based on the structure. First, as per structure, joints are classified into three categories: Fibrous, Cartilaginous, and Synovial.

Fibrous Joints

1. Fibrous Joints do not allow movements; therefore, they are Immovable joints or Fixed joints or Synarthrosis.
2. These joints connect by dense connective tissue consisting of primary collagen fibres and do not have a joint cavity.
3. They protect internal organs, strength to the body and stability to our body structure.
4. Syndesmosis,  Gomphosis, and Sutures are different types of fibrous joints.
   (a) Sutures are found in our skull bones with dentate margins.
5. Other examples of a fibrous joint are the rib cage, pelvic girdle, backbone, and upper jaw.

Cartilaginous Joints

1. This is also known as Amphiarthrosis, which allows limited movement. 
2. In this type of joints, the bones involved are joined together with the help of cartilages.
3. The joint between the adjacent vertebrae in our vertebral column is of this pattern.
4. Synchondroses and Symphyses are two types of cartilaginous joints.
5. The sternocostal joint is an example of the cartilaginous joint.
6. The pubic symphysis of the pelvis is a cartilaginous joint. 
   (a) This is found in the pubic regions of the right and left hip bones are strongly anchored to each other by fibrocartilage.

Synovial Joint

1. Synovial joints or Diarthrosis have a fluid-filled synovial cavity and irregular dense tissues that form the articular capsule. 
2. This is a perfectly movable joint and allows movements in one or more planes.
3. This joint helps in locomotion and many other movements.
4. A synovial capsule covers a synovial joint; the synovial fluid secreted by the synovial capsule lubricates and nourishes the joint.
5. There are six types of synovial joints mentioned in the table below.

Types of Synovial Joints	Structure	Function	Location
Ball and Socket Joint	It is formed by fixing bones into the cavity of other bones.	Ball and socket joints provide movement in multiple planes.	Shoulder and hip joints are examples of this type of joint.
Saddle Joint	This joint is formed between whose articulating surfaces have both concave and convex regions.	The saddle joint shows movement in two planes.	The saddle joint is located between the carpal and metacarpal of the thumb.
Hinge Joint	This joint is formed by the articulation of two or more bones.	Hinge joints provide movement in one plane.	Hinge joints are found in the knee and elbow joints.
Condyloid Joint	This joint is the modified form of the hinge joint.	Condyloid joints allow movement in two planes.	Condyloid joints are found in wrist bones. Joints between metacarpals and phalanges are of this type.
Pivot Joint	It consists of the rounded end of one bone that fits into the ring of another bone.	The pivot joint helps in rotation around the axis.	Pivot joints are present between the atlas and axis and wrist bones.
Gliding Joint	This joint between two bones where the surface of the bones is almost flat enables the bones to slide over each other.	The gliding joint allows sliding movements.	Gliding joints are found between the carpals.

Types of Joints Based on Functions

Joints can be classified into three categories based on functions: immovable or Synarthrosis joints, partly movable or Amphiarthrosis joints, and movable or Diarthrosis joints.

Types of Joints	Movement
Immovable	This type of joint does not allow any movement.Example: skull sutures, articulation of bony sockets and teeth.
Partially Movable	This type of joint allows limited movement.Example: distal joint between tibia and fibula and the vertebrae of the spine.
Movable	This type of joint allows movements in one or more axes. Example: elbow, shoulder, and ankle.

Joints and Their Movement

These are the few common joints and their movements.

Joint	Type	Movement
Elbow	Hinge	Flexion and Extension
Knee	Hinge	Flexion and Extension
Hip	Ball and Socket	Flexion, Extension, Abduction, Adduction, rotation, and Circumduction
Shoulder	Ball and Socket	Flexion, Extension, Abduction, Adduction, rotation, and Circumduction

Additional Information: Lever System

A lever system is a rigid bar where movement takes place along the joint on a fixed point called the fulcrum of the lever. Joints in the human body also function as levers. Let us have a look at how the joints can be classified as levers. The three types of levers are:

Type of Lever	Example
First-Class Lever (fulcrum between effort and load).	Found between the atlas vertebra and occipital bone of the skull. When the head moves up, the common is the fulcrum, contraction of the back muscle is the effort and the facial portion of the skull acts as load or resistance.
Second Class Lever (load is between fulcrum and effort)	Found in the ankle joint. When the human body is moved upwards on toes, the ball of the foot is the fulcrum, the contraction of calf muscles to pull the heel upward is the effort, and the body is the load or resistance.
Third Class Lever (effort is between fulcrum and load)	Found in the elbow of the forearm. At the time of biceps curl, the elbow joint is the fulcrum, the contraction of the biceps brachii muscles is the effort, and the weight of the forearm is the load or resistance.

Function of Joints

These are the main functions of joints:

1. It permits stability to the skeletal system.
2. It helps in walking, running, lifting things, grasping, and gripping an object.
3. It protects vital organs of our body by providing a protective enclosure.
4. It helps in multiple movements of our organs.

Disorder of Joints

Common disorders of the Joints are:

1. Arthritis: Inflammation of joints. It results in pain, swelling, and stiffness of the joint, and over a period, it can damage the joint. This can be of many types like Rheumatoid arthritis, Osteoarthritis, etc.
2. Gout: Inflammation of joints due to accumulation of uric acid crystals. This is also called gouty arthritis.
3. Bursitis: Inflammation of fluid-filled sac (Bursa) that cushions the joints.

Do You Know?

Summary

A Joint or Arthrosis is a part where two or more bones meet. In general, a human body has around 300 joints altogether, which works in a specific way to complete different functions of the human body. Fibrous, cartilaginous, and synovial are the three types of joints in our body. The basic function of joints is to provide structural stability and to allow movement. 

Frequently Asked Questions

Q.1. How to make bones and joints strong?
Ans: Bones and joints can be made stronger by eating an anti-inflammatory diet and maintaining body weight.

Q.2. How many joints are there in the human body?
Ans: There are around 250 to 350 joints in the human body.

Q.3. Why do bone joints make a sound?
Ans: The sound comes from the air bubble in the synovial fluid that gets trapped and then released during movements. 

Q.4. How to lubricate joints?
Ans: We can lubricate joints by consuming a lot of water and food containing omega-3 fatty acids.

Q.5. What is arthritis?
Ans: Inflammation of joints. It causes swelling, stiffness, and pain in the joint and over a period it can damage the joint. 

Q.6. What is the strongest joint in the body?
Ans: The strongest joint in the body is the Hip.

Q.7. What is the study of joints called?
Ans: Study of joints is called Arthrology (Greek Arthros = joints; Logos = study). 

Q.8. What is the anatomy of a joint?
Ans: Synovial joints have a fluid-filled synovial cavity and irregular dense tissues that form the articular capsule. A synovial capsule covers a synovial joint; the synovial fluid secreted by the synovial capsule lubricates and nourishes the joint.

Q.9. What is Kinesiology?
Ans: Kinesiology is the scientific study of human or non-human body movement. Kinesiology addresses physiological, biomechanical, and psychological dynamic principles and mechanisms of movement. 

Q.10. What is a joint function?
Ans: These are the main functions of joints:
1. It permits stability to the skeletal system.
2. It helps in walking, running, lifting things, grasping, and gripping an object.
3. It protects vital organs of our body by providing a protective enclosure.
4. It helps in multiple movements of our organs.

Now that you are provided with all the necessary information on Joints in Human and we hope this detailed article is helpful to you. If you have any questions about this article, ping us through the comment box below and we will get back to you as soon as possible.