How Do Synovial Joints Work in the Human Body?
We may say that a joint is a point where two or more things are connected. In this joint of the human body, it is the place where two bones connect. Joint means a junction or in other words, a strong connection that connects the bones, cartilage and together. Joint is necessary for all time movement in the body involving bones. Muscles generate force used to carry out movements through various joints. The ease and degree of movement at different joints vary with a lot of different factors. They can be classified based on two things.
Classification of Joints
Immovable
A joint which does not allow any kind of movement is known as Synarthrosis. The suture of the skull and gomphosis connecting teeth to the skull are some examples of synarthrosis.
Slightly Movable
The slightly movable joint is called amphiarthrosis, which usually allows very little movement at one of the joints.
Examples of this amphiarthrosis are some of the intervertebral disks present in the spine and also pubic symphysis located in the hip and lower portion of the body.
Freely Movable
These kinds of freely movable joints are known as diarthrosis joints. Diarthrosis is said to have the highest degree of moving of any kind of joint and also includes the elbow, the wrist, shoulder, and knee.
These joints, also classified based on the structure of the material present in the body, are as follows:-
A fibrous joint
Cartilaginous joints
Synovial joint
Synovial Joint
This is the most usable and most common kind of joint, which is found between bones that move against each other. A synovial joint is called diarthrosis, joins cartilage or bones with a fibrous joint. These joints allow bones to rotate around each other and to slide past each other. The synovial joint has a joint cavity filled with fluid, together with muscles, ligaments, tendons, the capsule keeps the bones of the joint in place. This arrangement allows movements. The membrane that lines up the capsule produces oily synovial fluid and lubricates the joints, reducing friction and wear and tear.
Structural Features of Synovial Joints
These joints are explained by the presence of a joint cavity and their walls are formed by articular capsules. Synovial joints are more complex than the other types of joint and their structural components include
Synovial fluid
Articular capsule
Articular cartilage
Reinforcing ligaments
Joint cavity or capsules
Types of Synovial Joints
Synovial joints are also called diarthrosis joints and almost all the joints present in our body are synovial joints. There are almost six different kinds of synovial joint and mainly classified based on their shapes of the articulating surface of bones that form each other.
Plane Joints
Plane joints are also known as gliding joints or arthrodial joints. Plane joints allow sliding and gliding movements that the articular surfaces of the bones are flat meaning they only allow movement to occur in uniaxial joints.
Plane joints present between ankle joints and carpals of the wrist that produce different types of movements are:-
Twisting
Back-and-forth
Nonaxial movement
Hinge Joints
Hinge joints are the types of joints with cylindrical projections, which hardly resemble the hinge of a door or a window. These are uniaxial joints with a single plane motion that permit extension.
The hinge joints are located in the elbow.
Pivot Joints
Pivot joints are known as a trochoid joint, rotary joint, in vertebrate anatomy, a freely movable joint that allows only rotational movement around a single axis. The moving bones rotate within a ring that is formed from an adjoining ligament and second bone.
Examples of pivot joints are the first and second bones of the neck which allows the head to move back and forth. Joint of the wrist, that allows the palm to move.
FAQs on Synovial Joints: Definition, Types & Importance
1. What is a synovial joint?
A synovial joint is the most common and freely movable type of joint found in the human body. It is uniquely characterised by a fluid-filled space, known as the synovial cavity, which separates the articulating bones. This structure allows for a wide range of smooth, frictionless movements.
2. What are the key characteristics of a typical synovial joint?
A typical synovial joint has several distinct features that facilitate movement and provide stability. These include:
Articular Cartilage: A smooth layer of hyaline cartilage that covers the ends of the bones, reducing friction.
Joint Capsule: A fibrous sac that encloses the joint, providing strength and support.
Synovial Cavity: The space between the bones that is filled with synovial fluid.
Synovial Fluid: A viscous fluid that lubricates the joint, absorbs shock, and nourishes the cartilage.
Reinforcing Ligaments: Tough bands that connect bone to bone, preventing excessive movement.
3. What are the six main types of synovial joints, with examples from the human body?
Based on the shape of their articulating surfaces, synovial joints are classified into six main types:
Ball-and-Socket Joint: Allows multi-axial movement. Examples include the shoulder and hip joints.
Hinge Joint: Permits movement in one plane (flexion/extension). Examples include the elbow and knee joints.
Pivot Joint: Allows rotational movement around a central axis. An example is the joint between the first and second cervical vertebrae (atlas and axis).
Gliding (Plane) Joint: Allows for limited gliding movements. Examples are the joints between the carpal bones in the wrist.
Saddle Joint: Allows movement in two planes, like a rider in a saddle. The prime example is the carpometacarpal joint of the thumb.
Condyloid Joint: Permits movement in two planes but no rotation. An example is the knuckle (metacarpophalangeal) joint.
4. Why is synovial fluid crucial for the proper functioning of these joints?
Synovial fluid is vital for several reasons. Firstly, it acts as a lubricant, significantly reducing friction between the articular cartilages during movement. Secondly, it functions as a shock absorber, distributing pressure and protecting the joint from impact. Lastly, it is responsible for transporting nutrients to the articular cartilage and removing metabolic waste, as cartilage lacks a direct blood supply.
5. How does the structure of a synovial joint directly enable a wide range of motion?
The structure of a synovial joint is perfectly adapted for mobility. The presence of a synovial cavity means the bones are not directly connected, allowing for a greater degree of freedom compared to other joint types. The smooth articular cartilage and lubricating synovial fluid work together to create an almost frictionless surface, enabling bones to glide past one another effortlessly and perform complex movements.
6. What is the primary difference between a synovial joint and a cartilaginous joint?
The primary difference is the presence of a joint cavity. Synovial joints possess a fluid-filled synovial cavity, which allows them to be freely movable (diarthroses). In contrast, cartilaginous joints have no joint cavity; the bones are directly joined by cartilage, which restricts movement, making them only slightly movable (amphiarthroses).
7. What happens to a synovial joint in a common disorder like osteoarthritis?
In osteoarthritis, the protective articular cartilage within a synovial joint progressively degenerates and wears down. This loss of cartilage leads to increased friction between the bones, causing pain, inflammation, and stiffness. As the condition worsens, the amount of lubricating synovial fluid can decrease, and bony spurs may form, further limiting joint mobility and function.
