Joints: Structure, Types, Functions, Practice Problems and FAQs

We all are worried about our looks. You all know that our skeletal system plays an important role in giving this look. You all know that the skeleton must have something that holds it together right? Because if that was not the case we would just collapse into a pile of bones as the bones would slip over each other and fall. Just like we see the skeletal system down. 

                                              GIF: Skeletal system

So what is that thing that holds our bones together? These structures are called joints. The whole skeleton is held together by joints. Joints are what make the body whole. It is also what lets us do most actions that we do on a daily basis. Did you know, there are places in our bodies where bones meet but don’t move at all! For example, the skull is a primary example of this. When we were born, we had bony plates in our heads separated by connective tissue that allowed our skull and brain to grow. As the time passes, these are replaced by ‘sutures’, bony material that connects the various plates. Yes, these are considered joints, but they don’t move. Now you feel more interested. Let us see more about joints in this article.

Table of contents

• Joints
• Types of joints
• Function of joints
• Practice problems
• FAQs

Joints

Joints are points of articulation between bone and bone, or bone and cartilage. These hold our skeleton in place and stop us from falling into piles on the floor. Due to the presence of a number of joints, the movement of the different body parts and the whole body is possible. But there are exceptions also as we discussed in the introduction. 

Types of Joints

On the basis of structure and mobility, there are three types of joints as follows:

• Fibrous joints (where there is no movement present)
• Cartilaginous joints (where only slight movement is present)
• Synovial joints (where there is presence of considerable movements)

                                                                 Fig: Types of joints

Fibrous joints or fixed joints

Fibrous joints will not allow any movement. Here there is no space between the bones and bones are held together firmly. This type of joint is present in the flat skull bones which normally fuse end-to-end. This is done with the help of dense fibrous connective tissues and they form sutures. It results in the formation of the cranium or skull. Sutures are the point of fusion of skull bones. The articulation of the roots with sockets of maxilla and mandible are also examples of this type of joint.

                                                                 Fig: Fibrous joint

Cartilaginous joints or slightly movable joints

In these types of joints, the bones involved are joined together normally with the help of fibrocartilages. These joints are also called symphysis. The joint between the adjacent vertebrae in the vertebral column is an example for this type of joint and it permits limited movements. Another example is the joints at the pubic symphysis. 

                                Fig: Cartilaginous joints

Synovial joints or freely movable joints

Synovial joints allow considerable movement. They are present between articular cartilage, and found in several places across the body. These joints help in many types of movements that we make. The fluid in the cavity acts like the engine oil in the car engine. 

Structure of synovial joint

A synovial joint possesses the following parts: 

Synovial cavity

It is the space between the two articulating bones that is filled with synovial fluid. 

Joint capsule

It is the fibrous capsule seen in continuation with the periosteum of articulating bones and it joints the articulating bones. It is highly innervated. It does not possess blood and lymph vessels and hence receives the nutrition from the surrounding blood supply through diffusion or by convection (exercise). It consists of two layers such as the outer fibrous membrane (contains ligaments) and the inner synovial membrane. Synovial membrane secretes the shock absorbing, lubricating, and joint-nourishing synovial fluid.

Articular cartilage

The bones of a synovial joint are normally covered by a layer of hyaline cartilage. It lines the epiphysis of the joint end of bone. It provides a smooth and slippery surface. This cartilage absorbs shock and reduces the friction during movements.

                                                 Fig: Synovial joint

Types of synovial joints

Based on the location the synovial joints are divided into six different types as follows: 

• Gliding joint
• Condyloid joint 
• Hinge joint 
• Ball and socket joint
• Saddle joint
• Pivot joint

Pivot joint

The pivot joint is also called the rotary joint or trochoid joint. It is characterised by one bone that can swivel in a ring formed from a second bone. Examples include the joint between the first (atlas) and second vertebrae (axis) in the neck. It is also seen between the radius and ulna. 

                              Fig: Pivot joint

               GIF: Pivot joint

Gliding joint

The gliding joint is also called the plane joint. It allows limited movement and is characterised by smooth surfaces that can slip over one another. Rotations or twisting is not possible because the bones are packed closely together by ligaments. It is found between the carpals of the hand and tarsals of the feet. 

                     Fig: Gliding joint

                GIF: Gliding joint

Condyloid joint

It is also called the ellipsoid joint. This joint allows movement in two directions such as side to side and back and forth. But it does not allow any rotation. In this joint an oval shaped condyle of one bone fits into an elliptical concavity of the other. Examples include the joint between the metacarpals and phalanges of the fingers. It is present in the wrist. 

                     GIF: Condyloid joint

Ball and socket joint

Ball and socket joint permits movement in all directions. This joint features the rounded head of one bone sitting in the cup of another bone. It is the most freely movable joint. Examples include shoulder joint and hip joint. 

Shoulder joint

In this joint the head of the humerus fits into the glenoid cavity of the pectoral girdle.

Hip joint

In this joint the head of the femur fits into the acetabulum of the pelvic girdle. 

            Fig: Ball and socket joint

Hinge joint

The hinge joint allows movement only in one plane. In this joint reel like surface of one bone fits into the concave surface of the other bone. Examples include elbow joint and knee joint. It is also present in the articulation between the occipital condyles of the skull and atlas vertebra. 

              Fig: Hinge joint

                    GIF: Hinge joint

Saddle joint

In this type of joint, a projection of one bone fits in saddle-shaped depression in another bone. It allows side to side and back and forth movement. But will not allow rotation movement. Examples include the joint between carpal and metacarpal of the thumb.

                  Fig: Saddle joint

                  GIF: Saddle joint

Function of joints

The main functions of the joints are as follows:

• It hold bones together
• It helps the skeletal system to bear the weight of the body.
• It allows movements in coordination with muscles.

Practice Problems

Q 1. Match column I with column II and find out the correct option from below. 

a) a - i, b - ii, c - iii
b) a - ii, b - i, c - iii
c) a - ii, b - iii, c - i 
d) a - iii, b - ii, c - i

Answer: Joints are the articulations between bones or bones and cartilages. They are important for the movement of bony parts. There are three types of joints as follows:

• Fibrous joints - They are commonly found in the skull where flat skull bones are connected by the dense white fibrous connective tissues. This type of joint does not allow any movement. The points of fusion between the skull bones are called sutures.
• Cartilaginous joints - Bones are joined together with the help of flexible connective tissue called cartilages here. This type of joint allows limited movement. Examples include the joints between the adjacent vertebra in the vertebral column.
• Synovial joints - These are the joints which allow considerable movement as they contain synovial fluid (thick and clear lubricating liquid) between the articulating (joining) surfaces of two bones. In this, bones articulate with each other like joints of the shoulder, hip, elbow, etc. Hence the correct option is a.

Q 2. Which prevents the leg bones from rubbing against each other when the knee moves back and forth while a person walks? 

a. Smooth muscle sheath
b. Articular cartilage
c. Synovial fluid
d. Both b and c

Answer: The joint here is a type of synovial joint called the hinge joint. A layer of smooth articular cartilage is present between the articular (adjoining) surfaces of the bones in this joint. Along with it, a clear thick liquid is present between the joints called synovial fluid. It lubricates the surfaces that glide past each other. Hence, it prevents the bones from rubbing against each other when the knee moves back and forth while a person walks. So the correct option is d.

Q 3. Which of the following options is not correct?

a. Joint - Between the humerus and pectoral girdle
Type - Ball and socket joint

b. Joint - Between the atlas and axis
Type - Pivot joint

c. Joint - Between the carpal and metacarpal of thumb
Type - Hinge joint

d. Joint - Between the carpals
Type - Gliding joint

Answer: Joints are points of articulation between bone and bone, or bone and cartilage. The common examples of joints in the given question are as follows:

• Saddle joint - Examples include carpometacarpal joint. It is the joint between carpal and metacarpal of the thumb. It does not allow rotation but allows back and forth and side to side movements.
• Pivot joint - Examples include the joint between the atlas (first cervical vertebra) and axis (second cervical vertebra). It allows swivelling movement. It is also called rotatory or trochoid joints.
• Hinge joint - Examples include elbow and knee joint. It is made up of two or more bones with articular surfaces that are covered by synovial fluid which reduces friction.
• Ball and socket joint - Examples include hip and shoulder joints. It is a type of joint which allows movement in all the three planes. It is also called spheroidal joints.
• Gliding joint - Examples include the joint between the carpals and tarsals. It permits limited movement and allows slipping of one smooth surface over another. It is also called a plane joint. Hence the correct option is c.

Q 4. What are the different types of synovial joints? Explain them.

Answer: Synovial joints allow considerable movement. They are present between articular cartilage, and found in several places across the body. Based on location synovial joint is divided into six different types as follows:

• Saddle joint - Examples include carpometacarpal joint. It is the joint between carpal and metacarpal of the thumb. It does not allow rotation movement but allows back and forth and side to side movements.
• Pivot joint - It allows swivelling movement and is present between the first and the second cervical vertebrae i.e atlas and axis. It is also called rotatory or trochoid joints.
• Hinge joint - Examples include elbow and knee joints. The hinge joint allows movement only in one plane. It is made up of two or more bones with articular surfaces that are covered by synovial fluid which reduces friction.
• Ball and socket joint - Examples include hip and shoulder joints. It is a type of joint which allows movement in all the three planes. It is also called spheroidal joints.
• Gliding joint - Examples include the joint between the carpals and tarsals. It permits limited movement and allows slipping of one smooth surface over another. It is also called a plane joint.
• Condyloid joint - It is also called the ellipsoid joint. This joint allows movement in two directions such as side to side and back and forth. But it does not allow any rotation. In this joint an oval shaped condyle of one bone fits into an elliptical concavity of the other. Examples include the joint between the metacarpals and phalanges of the fingers. It is present in the wrist.

Q 5. What are joints? State its function .

Answer: Joints are points of contact between bone and bone, or bone and cartilage. These hold the skeleton in place and stop us from falling into piles on the floor. The main function of the joint is to hold bones together, bear the weight of the body, and allow movement in coordination with muscles.

Q 6. Explain the different types of joints?

Answer: Joints are points of contact or articulation between bone and bone, or bone and cartilage. On the basis of structure and mobility, there are three types of joints as follows: 

• Fibrous joints - These joints do not allow any movement. This type of joint is shown by the flat skull bones which fuse end-to-end with the help of dense fibrous connective tissues in the form of sutures, to form the cranium. Sutures are the point of fusion of skull bones.
• Cartilaginous joints - The bones involved are joined together with the help of cartilages here. The joint between the adjacent vertebrae in the vertebral column is of this pattern and it permits limited movements.
• Synovial joints - They allow considerable movement. They have a fluid filled synovial cavity. They are present between articular cartilage, and found in several places across the body. These joints help in many types of movements that we make. Examples include the joint between carpals and metacarpals. 

FAQs

Q 1. How many joints are there in the human body?
Answer: The human body comprised 270 bones at birth. It later decreases to 206 due to fusion of some of the bones as we progress in age. The joints connect bone to bone or bone to cartilage. There are around 360 joints in the human body. 

Q 2. How are the joints named in a common way?
Answer: Joints are of three types as follows:

• Simple joint - It possesses two articulation surfaces. Examples include shoulder joint and hip joint.
• Compound joint - It possesses three or more articulation surfaces. Examples include radiocarpal joints.
• Complex joint - It possesses two or more articulation surfaces and an articular disc. Examples include knee joints. 

Q 3. Write down the number of joints present in the ankle?
Answer: The ankle possesses two joints. It is called the ankle joint or talocrural joint. It is a synovial joint that connects the bones of the leg such as the tibia and fibula, with the talus of the foot. It is considered as a complex hinge joint which possesses two articulations.

Q 4. How many bones are there in a baby?
Answer: Body of a baby possesses around 300 bones at birth. These bones eventually fuse to form the 206 bones. Some of the skeletal parts of the baby are made completely of cartilage whereas some other parts are partly made of cartilage.

Related Topics