Page 275 - New Medley 5 Semester 1

Voluntary muscles: These muscles are under our control. They are attached to the

bones. Hence, they are also called skeletal muscles. The arms, legs, hands, etc. have
voluntary muscles. That is why we can control our actions while running, jumping,

walking, etc.

Involuntary muscles: These muscles do not work at our will. They work without
our thinking about them. So, we cannot control them. Our stomach and heart

have involuntary muscles. The heart beats and the stomach digests food, even
while we are asleep.

Muscles are made up of thin and long cells called muscle fibres. There are three

types of muscle fibres.

Striated Muscle Fibres

All voluntary muscles are made up of

striated muscle fibres. They have dark and
light bands running across them.

Smooth Muscle Fibres Striated muscle Smooth muscle Cardiac muscle
fibres
fibres
fibres
Involuntary muscles are made up of smooth Types of muscle fibres
muscle fibres, which are long and narrow at the ends. These muscles do not have

any bands. Organs of the respiratory and circulatory systems have a lining of
smooth muscle fibres. They work for a long time without getting tired.

Cardiac Muscle Fibres

The word ‘cardiac’ relates to the heart. Cardiac muscles are present only in the
heart. They have bands like striated muscle fibres. They are strong and do not

get tired. That is why our heart works continuously.

Working of Muscles
Muscle cells are the only cells in our body

which have ability to contract (shorten) and relax
(lengthen). Thus muscles move the body parts

by contraction and relaxation. The contraction
of muscle cells causes a body part to bend at a

joint while the relaxation allows the body part
to straighten again at the joint. Movement of fingers due to
working of muscles

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