Bones ’n’ muscles in motion
 

A diagram showing ball-and-socket joint at the hip.

Who isn’t familiar with the human form? Everyone of us knows what exactly a human being looks like, at least on the exterior, but few of us are really familiar with what’s inside us, hidden by the largest organ of the body - the skin! We have only seen the parts inside our bodies in pictures, scans, X-rays or through medical exhibits. So, let’s take a peek into the human body - to see what’s beneath the skin.

Initially, we’ll check out the bone structure or the skeleton as it’s called because it plays a key role. It is the skeleton that supports the body, anchors the muscles and protects various organs, like the heart, brain and lungs.

In fact, it is the bones that give the human body structure and form. If not for the skeletal system, your body will crumble up into a shapeless mass of skin and flesh. You’ll end up a puddle of skin and guts on the floor! How weird that would be.

The human skeleton as you may already know comprises 206 bones. These bones are formed by living matter nourished by blood. There are different kinds of bones that make up the skeleton; big bones, small bones, long bones and short bones which are called by various names.

Long bones, such as thigh bones, consist of bone marrow, in which red and white blood cells are formed. Bone marrow by the way is a yellow, jelly-like substance. It is organic matter.

Different bones have different functions. For instance, the bones in the head - called the cranium or skull protects the vital organ and the major part of the nervous system, the cerebrum or the brain and also the eyes, middle and inner ears.

It’s like a helmet. The rib cage protects the spine and the sternum organs such as the lungs, major blood vessels and the heart. The vertebrae or the spinal column is what supports the spinal cord and keeps the skeletal structure upright.

As each bone in the body has a special job to do, they all have to work together; they help you to stand tall, protect the inner parts of the body and store minerals for use by cells in other parts of the body.

The tiniest bone in your body is called the stirrup and guess where it’s located? Inside your ears! The largest bone or femur is in your upper leg. More than half the bones in your body consist of the tiny bones in your hands and feet.

We know that the bones help form the human structure, but how do these bones, which are so stiff and solid help you to bend your arms and legs, hands and feet, and the neck and spine?

With the assistance of joints (the area where two bones come together). These joints are held together with something called ligaments - bands of tough fibrous connective tissues. The sockets of some of the joints are lined with a fluid that makes movement easy in most parts of the body.

In the event bones can move with respect to one another, the joint is said to be articulated. At all articulated joints in your body such as the elbows and knees, the bones are held together by the tough cords - ligaments.

There is also a pad of cartilage between the bones to absorb any shocks and trauma the body is subjected to by way of accidents. Do you know that there are 26 very small bones with articulated joints between them in your hand? If not for them, you will not be able to move your fingers at all. You are able to have such flexible hands because of these special joints.

However, not all bones have joints. For instance, the skull is formed of eight flat fused bones, not jointed ones. But there is one moveable bone in the skull and what do you think that is? The lower jaw. It is what allows you to open and close your mouth and chew your food too.

Now, how many bones do you think you have on your face? Just 14! But what’s amazing is the fact that both humans and giraffes have the same number of bones in the neck. It’s no joke because when comparing the length of a human neck and that of a giraffe it sure seems impossible. But the reason for this huge difference is that the neck vertebrae of a giraffe are much longer than a human beings’.

There are two major systems of bones in the human body that is the axial skeleton comprising 80 bones which includes the skull, ribs and sternum, and the appendicular skeleton comprising 126 bones which includes the shoulder, pelvis and attached limbs.

As mentioned before, not all these bones are the same. There are fused bones and individual bones. All these bones are supported by ligaments, tendons, muscles and cartilage.

Muscles! They are another important part of the body that enables motion.

There are over 500 muscles that allow the skeleton to move. Muscles are attached to the bones by tendons. When a muscle contracts, its tendon pulls on the bone and makes it move.

There are smooth muscles and striated muscles. The smooth muscles are found in the digestive tract, reproductive organs, bladder, arteries and veins. The striated muscles are located in the legs, arms, back and torso.

There are also voluntary muscles (those of the hand, the arms and the legs). Then there are involuntary muscles which are not connected to the bones and work without your intervention - they are the heart, the muscles of the stomach and the thorax. But, apart from these, most muscles are controlled by the brain.

Not all the muscles in the body are alike. Like the bones, they too differ. So, muscles may be long, short, thin, flat or even in the form of rings.

Do you know that muscles work in pairs? The actions of muscles involve contraction and relaxation. You can see how the muscles work in pairs if you look at a picture of the muscles in the upper arms. When the arm is bent, the biceps contract and the triceps are related. And when the arm is stretched out, the biceps are relaxed and the triceps are contracted.

In this manner, so many muscles are at work each time you take a step, lift your hands, jump up or even turn a page in this newspaper.

Did you know that about hundred different muscles are used simply for walking? Isn’t it fascinating how the bones and muscles in your body work together with other parts to keep you strong and active? Learn more about this wonder machine beneath the skin.

Facts and pix: Internet and Fact finder

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Quick facts

* At birth, humans have about 270 bones. But as adults the number of bones is reduced to 206. What do you think happened to the rest of the bones? Many of the small bones fused together during growth.

* In an adult, the skeleton comprises 13 per cent of the total body weight.

* Three bones in each middle ear known as ossicles articulate only with each other.

* The hyoid bone (on the neck) serves as the point of attachment for the tongue. It doesn’t articulate with any other bones.

* The human skeleton has six main functions. They are movement, protection, blood cell production, storage and endocrine regulation.

* There are many differences between the male and female skeletons. For example, a woman tends to have a narrower rib cage, flatter, more rounded and proportionally large pelvis, more rounded shoulders and more pronounced carrying angle of forearms.

* The pelvis and the cranium (skull) are fused bones.

* The nose and ears are made of cartilage, a flexible substance which is not as hard as bone.

* There are different types of joints; fixed joints (like the skull), hinged joints (fingers and toes) and ball-and-socket joints (shoulders and hips).

* The stirrup measures between 2.5 and 3.8 mm (0.1 and 0.15 in). It weighs between 2 and 4.3 mg.

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