Main->Readings->5th Grade Readings->Skeleton and Muscles->Part 2

Part 2: Bones and Joints

Bones of the torso

There are two main parts to your skeleton: the bones of your head and torso), and the bones in the arms and legs. (The torso is the main trunk of your body, including your chest and abdomen.)

The bones in the head and torso (known as the "axial skeleton") have complicated shapes. If you look at the vertebral column (what we usually call the backbone) from the side, it is not a straight line, but curved like the letter S, and it is not really just one bone. The backbone is made of over 30 separate bones called vertebrae (VER-tuh-bray). Because it is made of so many bones, the backbone can bend and twist in many different directions.

At one end of the backbone is a very important set of bones, the skull. Part of the skull protects the brain, while part of the skull forms the jaw. The rib cage is attached to the vertebral column a little lower down. The ribs form a light cage around the chest and protect the heart and lungs.

At the lower end of the backbone is the pelvis, a group of wide, large bones which protects the organs and keeps them in place. The pelvis also anchors the legs. Above the rib cage, the collarbones ("clavicles") and shoulder-blades ("scapula") help anchor the arms.

Joints

Bones can move because of the way they are joined together. The place where two or more bones come together is called a joint. The bones at a joint are held together by strong bands of tissue called ligaments which allow the bones to move. However, there are several different kinds of joint, and each one moves differently.

The ball-and-socket joint is found in the hip-bone and the shoulder and allows the most movement of all the joints. One bone (like the femur my student found) has a ball-like knob at the end of it, and the knob fits into a cup-like space on the other side. The ball-and-socket joint is what allows baseball pitchers to throw a ball with such tremendous speed.

The sliding joint is found in the vertebral column and allows small sliding movements. The vertebrae have pads of cartilage between them, and the bones slide over these pads. This is what makes the backbone so flexible.

The pivot joint allows movement turning from side to side, and your head is attached to your vertebral column with this joint. A hole in one bone fits over a pointed part of the other bone, so that one bone can turn on top of the other.

The hinge joint allows bones to move back and forth, and is found in your elbow and knee. It allows bones to move like a hinge in a door.

It might seem funny, but there is one type of joint which doesn't allow any movement at all. A joint between bones that do not move at all is called a fixed joint, and one place the fixed joint is found is in your skull. When babies are born, their skull bones are not joined together yet. In fact, there is a gap between them called the fontanel, or soft spot. However, the bones quickly grow together to protect the brain.

1. fixed joint 2. pivot joint 3. ball-and-socket joint 4. sliding joint 5. hinge joint

In fact, all your life the bones of your skeletal system are changing. They are constantly renewing themselves, making new bone tissue. That is because the bones inside your body are living organs, made of cells and tissues, working together to help your body live and move.

Homework

1. Name three bones of the skeletal system.
2. List two main types of joint and tell where in the body they can be found.
3. What are ligaments?
4. If you were designing a better human body, would the joints all be the same or would there be different kinds? Explain your answer.

If you like, take the quiz on Bones and Joints at www.funbrain.com The secret word is "drturner".

Go on to Part 3: The Muscular System

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This page last modified on April 7, 2003