Page 38 - Science - 5

These muscles do not get tired. This is why, your heart keeps working day and

night.

HOW DO MUSCLES WORK?
The body moves because of the action of

muscles which are made up of muscle cells.

The muscle cells are unique because they
are the only cells in the body that can

contract or shorten and relax or lengthen.

When a muscle cell relaxes, it returns to its
original size. This ability of the muscle cells

to contract and relax causes movements in

the body.

Strange but true

w Your bones consist of 50% water and 50% solid matter.

w When you were born, you had over 300 bones. As you grew, some of
these bones began to fuse together and now you have 206 bones.

These muscles work in pairs to cause movement. We can keep our muscles
strong and active by regular exercises and a balanced diet.

Scientific Terms

Bone marrow : soft fatty substance found inside long bones
Pelvic girdle : the enclosing structure formed by the bony pelvis

Pectoral girdle : the skeletal framework which provides attachment for the forelimbs

Socket : a natural hollow into which something fits
Unique : being the only one of its kind

Chapter at a Glance
³ The skeletal system is the framework of bones that gives shape and support to our

body.
³ The meeting point of two bones is called a joint.

³ The muscles attached to the bones make the movement of the bones possible.
³ Voluntary muscles are under our control whereas involuntary muscles work on their
own.

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