The Skeletal System
Category : 6th Class
The human skeleton or skeletal system is made up of 206 bones. A baby has 300 bones in all. But as it grows, some of the bones fuse together or join. Before we learn more about bones and the joints where they are joined together, let us take a look at the functions of the skeletal system.
The bones of our body act as a framework or give it shape. Without bones, our body could be a shapeless mass, e.g. like the body of a snail. The bones give our body support, like the pillars of a building or the frame over which an idol- maker makes an idol. The bones also protect delicate internal organs. For example, the skull protects the brain, which lies inside it, and the ribs protect the heart and lungs. The third function of the bones is to help us move. It is the movement of the bones that helps us bend, run, walk, and so on.
Twenty-two bones make up the skull. These are the hardest of all the bones in the body. Some of these form the cranium, or the cover for the brain. The rest are the facial bones, which give shape to the face. Two hollows, or sockets, formed by the facial bones protect the eyes. All the bones of the skull except the one forming the lower jaw are fixed firmly, and cannot move. Only the bone of the lower jaw is capable of movement, which helps us eat and speak.
Fig. Most of the bones of the skull are fixed. Only the lower jaw can move.
The spine is also called the vertebral column or backbone, the spine consists of 33 small bones known as vertebrae (singular: vertebra). The vertebrae are hollow at the centre and are joined together to form a tube, through which runs the spinal cord.
One of the functions of the vertebral column is to protect the spinal cord. The other functions are to hold the body up and help us bend forward, backward, sideways and twist from the waist.
Of the 33 vertebrae, seven are in the neck or down to the upper chest, 12 vertebrae are extended to the back, and five making up the lower back between the hips and chest. The last nine vertebrae are fused into two segments, coccyx and sacrum. They are fixed and make us to sit properly. Coccyx is also called tail bone. The vertebrae in the neck allow us to move our head from side to side and bend the neck forward and backward. The vertebrae also act like a spring, cushioning the head, so that the brain does not get jerked around when we run or jump.
Running through the centre of the chest is the breastbone, or sternum. Joined to it are 10 pairs of strong, flexible bones called ribs. The ribs curve around and join the chest vertebrae at the back, to form a protective cover for the lungs and heart, called the ribcage. Another two pairs of ribs are joined only to the backbone. These are called floating ribs. The ribs are attached to the sternum in such a way as to allow the ribcage to expand when we inhale, or breathe in.
The Shoulder Bones
You can feel the collar bones quite easily on either side of the neck. Quite often, they can be seen too. Each collar bone is attached to a shoulder blade and to the breastbone. The shoulder blade and collar bone not only give shape to the shoulder, but also help in the movement of the arm. The top of the upper arm bone fits into the shoulder blade in such a way as to allow the arm to move freely. The human shoulder allows more mobility than the shoulder of most other mammals.
The Bones of the Arm and Hand
The arm has two parts, the upper arm and the forearm, joined at the elbow. One long bone runs through the upper arm, while two bones give shape to the forearm. The bone of the upper arm is joined to the bones of the forearm at the elbow and fits into the shoulder blade at the shoulder.
The bones of the forearm are also attached to the wrist, which is formed by eight small bones. Five long bones form the palm. They are joined to the wrist bones at one end and the finger and thumb bones at the other end. Each finger has three bones, while the thumbs have two bones.
The Hip Bones
Each hip bone is formed by three bones fused together. The two hip bones are joined to the five fused vertebrae in the hip region. The two hip bones are referred to as the pelvis, and together with the vertebrae they are joined to, form the pelvic girdle. The thigh bones fit into depressions or sockets in the hip bones.
Fig. The hip bones
The pelvis, or rather the pelvic girdle, helps us walk, run, stand and sit. It supports the weight of the body when we stand or sit and transmits the movement of the legs to the whole body.
The Bones of the Leg
One long bone runs through each thigh. One end of each bone is attached to the pelvis. The other end is attached to the leg bones at the knee. The thigh bones are the largest bones in the body.
Each leg has two bones joined to the thigh bone at one end, and the ankle bones at the other. Each ankle is made up of seven bones, which are attached to the five bones that run through most of the foot. The five bones of the foot are attached to the bones of the toes. All the toes, except the big toe, have three bones each. The big toe has only two bones.
The bones of the foot and ankle are arranged in such a way that they form an arch or bridge. This arch helps to support the weight of the body when we stand, walk or run. People who do not have this arch, or are flat-footed, find it difficult to walk or run for long stretches.
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