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2. Involuntary Muscles: Some muscles work by themselves. They are not in our
control. They are called involuntary muscles. They work automatically. These
muscles help our lungs expand and contract, and our food to be digested.

3. Cardiac Muscles: An important involuntary muscle is the cardiac muscle.
Muscle of the heart is called cardiac muscle. It begins working seven months
before birth and stops working at death.

Let’s
Revise

Ÿ The human body is made up of about hundred billions of cells.
Ÿ Bones form the framework of our body and gives shape to it.
Ÿ Skeletal system holds the body and maintains the balance of the body.
Ÿ Muscular system holds all the bones together.
Ÿ Many voluntary and involuntary actions are performed by our muscular system.

Points to Remember

Cells : the basic building blocks of all living things.
Tissues : the group of cells that form part of an organ.
Femur : the largest bone in the human body

E XE R C I S E

A. Tick ( ü) the correct answer.
1. There are 206/208 bones in an adult human body.
2. Cells together form tissues/organs.
3. The femur/rib is the largest bone of the body.
4. The bones of the body are filled with a substance called muscle/marrow.
5. Knee/elbow is a hinge joint.

B. Tick (ü) the correct statements and cross (û) the wrong ones.
1. The longest bone is present in the thigh.
2. Involuntary muscles are in our control.
3. The skull is made up of twelve flat bones.
4. The heart is a voluntary muscle.
5. The hip is an example of a hinge joint.

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