Joints of Body

Question 1 What is a joint. Name the 4 types of joints in human body?

Question 2 Explain the working of elbow joint in human body?

Question 3 Explain the working of knee joint in human body?

Question 4 Define the term ligaments?

Question 5 What is a ball and socket joint?

Question 6 In which part of the body you will find pivot joint?

Question 7 What type of joint occur in our skull?

Question 8 What type of joint exist between upper jaw and rest of the skull?

Question 9 Which type of joint is hip joint?

Question 10 What is the function of ligaments in our body?

Also Read NCERT Solutions for Chapter 8 Body Movements

Joints

We can bend or move our body parts only at those places where two or more bones join together. Such places are called joints.

We can bend our arm at the elbow because the bones of the upper arm and lower arm form a joint at the elbow. The place where two or more bones meet in the skeleton is called a joint.

 

Most of the joints allow the bones to move. The amount of movement depends on the type of joint. We can move our head, arms, hands, legs and feet because all these parts have bone joints.

In the freely movable joints like elbow, knee, shoulder, hips the ends of the bones forming the joint are held in place by strong connective tissues called ligaments.

Ligaments connect the bones forming the joints and prevent the bones from falling apart during movement. Ligaments are, elastic and so they can stretch to let the bones move at the joints easily. The ends of the bones at joints are covered with a soft and smooth layer of cartilage. The layer of cartilage allow the ends of the bones to move over each other smoothly without fiction. This prevents damage to the ends of the bones due to wear and tear caused by rubbing over each other.

There is a thick oily liquid between the ends of bones of a freely movable joints. This oily liquid lubricants the cartilage at the ends of bones and reduces friction.

Types of Joints

Hinge joint

A hinge joint allows the movement of bones in only one direction i.e. forward and backward. In a hinge joint, the movement of bones is restricted to one direction by the shape of the ends of the bones which form the joint, and by the ligaments which hold the bones together at the joint.

In our body hinge joint occurs at elbow, knee, finger joints and jaw.

We can bend our arm only in one direction i.e. forward and backward. This is because our elbow is a hinge joint at the lower arm bones. The lower end of upper arm bone is in the shape of a knob and the upper end of the lower arm is in the shape of a cup. The knob of upper arm bone fits into the cup of lower arm bones to form a hinge joint at the elbow. The ligaments hold the upper arm bone and lower arm bone together at the elbow joint.

 

We can bend our legs in only one direction i.e. forward and backward, like a door on its hinges. The knee joint is a hinge joint. At the knee, the lower end of upper leg bone or thigh bone is in the form of a knob and the upper end of the lower leg bone is in the form of a cup. The knob of upper leg bone fits into the cup of lower leg bones to form a hinge joint at the knee. The ligaments hold the upper leg bone and lower leg bones together at the knee joint.

The joints between the bones of our fingers allow only a hinge like movement. So, the finger joints are hinge joints. The lower jaw also forms a hinge joint with the fixed bones of the skull.

Ball and Socket Joint

In the ball and socket joint, one end of the bone has a round shape like a ball which fits into a socket in the other bone.

In the ball and socket joint, the bones can be turned in any direction i.e. forward and backward, side to side and even rotated. The ball and socket joints occur at the shoulder and hips in our body.

A ball and socket joint allow much more movement of bones than a hinge joint.

If we stand up and move our arm around at the shoulder, we will find that we can move forward and backward, and from side to side, and we can also rotate it. This is because shoulder is a ball and socket joint. The head of upper arm bone is round like a ball and the shoulder blade bone has a socket in it. At the shoulder, the ball on the top end of upper arm bone fits into the socket in the shoulder blade to form a ball and socket joint. The ball shaped top end of the upper arm bones can rotate freely in the socket of the shoulder blade so that the arm can be moved in all directions.

If we stand up and move our leg around at the hip, we will find that we can move it forward and backward, and from side to side, and we can also rotate it. This is because hip joint is a ball and socket joint. The upper end of thigh bone is round like a ball whereas the hip bone has sockets. At our hip, the ball on the top end of thigh bone fits into the socket in hip bone to form a ball and socket joint. The ball of the thigh bone can rotate freely in the socket of hip bone so that the ball and socket joint at the hip allows the leg to be moved in all directions.

 

Pivot Joint

In a pivot joint, a cylindrical bone turns in a ring type bone. The pivot joint allow rotation around an axis. A pivot joint exist between our skull and the top vertebra of backbone. A pivot joint between our skull and neck allows our heads to bend up and down from side to side.

Pivot joint occurs in the forearm near the elbow. The forearm has two bones, radius and ulna. In the forearm, the pivot joint makes the radius and ulna bones to twist around each other. The pivot joint in forearm makes us turn our forearm to hold the palm of hand up or down.

Fixed Joints

In some joints, the bones are held so tightly together that they cannot move at all. Such joints are called fixed joints. The function of fixed joints is to provide strength and support to the body or to protect delicate organs which cannot withstand any kind of deformation.

Fixed joints occur in our skull. The plate type bones of our skull are held together by fixed joints and cannot move at all. The hard and strong skull protects a delicate organ of our body called brain.

Skull is made up of number of bony plates connected through fixed joints.

If we open our mouth wide, we will find that we can move our lower jaw away but the upper jaw does not move at all. We cannot move the upper jaw because it is connected to the skull by a fixed joint.

There is a fixed joint between the skull and the upper jaw. We can move the lower jaw because the lower jaw is connected to the skull by a movable joint called hinge joint. Fixed joint also occur in hip bone. The  fixed joints between various hip bones makes our hips very strong. The hip bone is connected to a backbone by a fixed joint.

Notes for Chapter 8 Body Movements Skeleton: Framework of Bones Joints of Body Muscle Contraction and Movement in Animals