Skeletal system


•      Every person has a skeleton made up of bones.

•      These bones give shape to our body, let us move in many ways, and protect our internal organs.

•      The skeletal system is the framework of bones that give support to our body.


What are bones made of?

•      If you've ever seen a real skeleton or fossil in a museum, you might think that all bones are dead.

Figure 10: Dinosaur fossil in a museum

•      Although bones in museums are dry, hard, or crumbly, the bones in our body are different.

•      The bones that make up our skeleton are all very much alive, growing and changing all the time like other parts of our body.

•      Every time we walk, settle into a chair, we're using our bones, muscles, and joints.

•      Without these important body parts, we wouldn't be able to stand, walk, run, or even sit.

Figure 11: Human skeleton



- Our skeleton can be observed by the special pictures (X-rays).

- A doctor decides when we need an X-ray and what body part needs to be x-rayed.

- Doctors can see broken bones and lung infections using X-ray machine.


•      Bones are filled with a jelly-like substance called bone marrow.


Figure 12: Skeleton made up of bones



•      Our skull protects the most important part of body -- the brain.

•      The skull is made up of different bones. Some of these bones protect our brain, whereas others make up the structure of our face.

•      If we touch beneath our eyes, we can feel the ridge of the bone that forms the hole where our eye sits.

Figure 13: Skull

•      The skull protects the brain, the skull of an adult human being generally contains 28 bones.

•      All bones in the skull are fixed, except the lower jaw.

•      The movable lower jaw enables us to talk and eat.

•      The upper and the lower jaw have teeth. Teeth help us in cutting and chewing food.


Rib Cage:

•      Ribs make a cage of bones around the chest, called the rib cage.

•      It's easy to feel the bottom of this cage by running our fingers along the sides and front of our body, a few inches below our heart.

•      If we breathe in deeply, we can easily feel our ribs right in the front of our body.


Figure 14: Rib cage

•      The rib cage protects our heart and lungs.

•      The first seven pairs of ribs attach in the front to the sternum– a long & strong bone in the centre of our chest that holds those ribs in place.

•      The ribs are also attached to the backbone. However, the last two pairs of ribs are not attached to the sternum, and so they are called floating ribs.

Figure 14: Floating ribs



•      The backbone protects the spinal cord.

•      lt is made up of a series of small bones called vertebrae.

•      The backbone (spine) lets us twist and bend, and it holds our body upright.

•      It also protects the spinal cord, a large bundle of nerves that sends information from our brain to the rest of your body.

Figure 15: Backbone (spine)

•      The backbone (spine) is special because it isn't made of one or even two bones.

•      There are 33 vertebrae (bones) that make the spine.



•      We have two pairs of limbs:



•      Our legs are attached to a circular group of bones called pelvis.

•      Our leg bones are very large and strong to help support the weight of our body.

Figure 16: Thigh bone-Femur

•      The bone that goes from our pelvis to our knee is called the femur.

•      The thigh bone or femur is the longest bone in the body.


Functions of Skeletal System:

•      The skeletal system is what keeps our body in shape, protects our vital organs, such as the heart, brain, and lungs, and enables us to move.

Human backbone- a part of skeletal system provides support to the body

  1. In our body, the skeleton works very closely with the muscular system to help us move.
  2. The bones create a framework to which our muscles and organs connect.
  3. Muscles contract and move the skeleton along.
  4. Our skeleton also plays a role in protection, especially in our head.
  5. It protects our soft internal organs.
  6. The skull protects the brain.
  7. The rib cage protects heart and the lungs.
  8. The backbone protects the delicate spinal cord.
  9. Bone marrow produces blood cells.

Figure 17: Bone marrow produces blood cells in our body

•      Both red blood cells and white blood cells are created in our bones.

  1. Our skeletal system is made up of cartilage and calcified bone that work together.



•      Cartilage is a tough, elastic substance.

Figure 18: Nose possess cartilage

•      It holds the bones in place where they join.

•      Cartilage also protects the bones.

•      Without cartilage, the bones would rub against each other and wear out.

•      Some organs, such as nose and ears, have cartilage.



•      Muscles are all made of the same material, a type of elastic tissue.

Figure 19: Muscles made up of an elastic tissue

•      Thousands or even tens of thousands, of small fibres make up each muscle.

•      Muscles hold the bones together and make movement possible.

•      They also help in important processes such as digestion.

•      There are three types of muscles in our body.

Figure 20: Three types of muscles


Skeletal Muscles:

•      Skeletal muscles are voluntary muscles, which mean the actions can be controlled by us.

Figure 21: Skeletal muscles

•      Our leg won't bend to kick the football unless we want it to.

•      The skeletal muscles work together with our bones to give our body– power and strength.

•      Some of our biggest and most powerful muscles are in our back & near our spine.

•      These muscles help keep us upright.


Smooth Muscles:

•      Smooth muscles sometimes also called involuntary muscles are usually in sheets, or layers.

•      We can't control this type of muscle.

•      But smooth muscles are at work all over our body.

Figure 22: Smooth muscles

•      In our stomach and digestive system, they contract (tighten up) and relax to allow food to make its journey through the body.


Cardiac Muscles:

•      The muscle that makes up the heart is called cardiac muscle. It is also known as the myocardium.

•      The thick muscles of the heart contract to pump blood out and then relax to let blood back in after it has circulated through the body.

Figure 23: Cardiac muscles

•      These muscles function automatically.

•      Just like smooth muscle, cardiac muscle works all by itself.



•      A joint is the place where two bones meet.

•      Most joints are movable.

•      They make the skeleton flexible — without them, movement would be impossible.

•      Fixed joints don't move at all.

•      Our skull has some of these joints which close up the bones of the skull.

•      There are four kinds of movable joints in our body.


Ball and Socket Joint:

•      This type of joint allows movement in many directions.


(a)                                  (b)

Figure 23: (a) Ball and socket joint (b) Hip joint

•      We can find these joints at our shoulders and hips.

•      They are made up of the round end of one bone fitting into a small cup-like area of another bone.


Hinge Joint:

•      One of the main types of moving joints is called a hinge joint.


(a)                                          (b)

Figure 24: (a) Hinge joint (b) Knee joint

•      Our elbows and knees each have hinge joints, which let us bend and then straighten our arms and legs.

•      These joints are like the hinges on a door.

•      Just as most doors can only open one way, we can only bend our arms and legs in one direction.

•      We also have many smaller hinge joints in our fingers and toes.

•      Bones in the knee, elbow, fingers, and toes have this type of joint.


Pivot Joint:

•      This type of joint is found between the first two vertebrae of our backbone.


(a)                                   (b)

Figure 25: (a) Pivot joint (b) A joint present between two vertebrae

•      It allows us to move our head up, down, and sideways.


Gliding Joint:

•      This type of joint is found in the bones of the wrist and the ankle.


(a)                                          (b)

Figure 26: (a) Gliding joint (b) Ankle joint

•      It allows these bones to slide against each other in a gliding motion.



•      Strengthen your skeleton by drinking milk and eating other dairy products (like low-fat cheese or yogurt).

•      Dairy products contain calcium, which helps bones harden and become strong.

•      When we use a skateboard, in-line skates, or a scooter, we must be sure to wear wrist supports and elbow and knee pads.

•      Another way to strengthen your bones is through exercise like running, jumping, dancing, and playing sports.