Maharashtra Board Class 7 Science Chapter 12 The Muscular System and Digestive System in Human Beings PDF Download

12. The Muscular System and Digestive System in Human Beings

1. What is meant by 'organ system'?

2. How are the bones in our body joined to each other?

Muscular System

Close your fist tightly and bend your arm at the elbow. Now feel the upper part of this arm with the fingers of your other hand. What did you experience? Did you feel the hardness in the upper arm? This fleshy part consists of muscle. Muscles contract and relax as different parts of our body move. Muscles give our body a specific shape and posture.

Muscles are bundles of fibres that can contract and relax as required.

What is the mutual relationship between muscles and bones?

Muscles are firmly attached to bones by means of tendons. When muscles contract, there is movement at the joint and the bones move either nearer to or away from each other.

The action of muscles is necessary for all kinds of movements – from the small movements of eyelids to those that demand great strength as when chopping wood with an axe. We use muscles for various movements like talking, laughing, walking, jumping, throwing, etc.

Which parts of our body are made up only of muscles?

Teacher's Note

Muscles help us do everything. When you play cricket, your arm muscles, leg muscles, and chest muscles all work together. This is how sports help us stay healthy.

Exam Trick

Remember: Muscles pull bones. They never push. When your biceps contract, your arm bends – that is pulling, not pushing.

Points to Remember

Muscles are bundles of fibres.
Muscles contract and relax to make movement.
Tendons join muscles to bones.
There are more than 600 muscles in the human body.
Muscles give our body shape and posture.

There are more than 600 muscles in the human body. Muscles contribute almost 40% of the weight of a healthy adult human body. There are about 30 muscles in the human face. Our eyes, mouth and nose are encircled by small muscles. Expressions like happiness, sadness, fear are expressed by the movements of these muscles of the face.

Are the muscles of the different organs in our body identical?

1. Voluntary muscles: Working with our hands, walking, eating, etc. are functions that depend upon our will. Muscles used in these actions are called voluntary muscles. For example, muscles in our arms and legs are voluntary muscles.

2. Involuntary muscles: Various processes like breathing, blood circulation, digestion are vital functions, i.e., they are essential for life. They do not depend upon our will. The muscles of organs which carry out these involuntary functions are called involuntary muscles. Functions of organs like the stomach, intestine, heart are carried out in their own fixed manner by involuntary muscles.

Which organs in our body have voluntary muscles and which ones have involuntary muscles? Find out and make a list of each type.

Types of Muscles

1. Skeletal muscles: The two ends of each of these muscles are attached to two different bones. Examples of such muscles are muscles of the arms and legs. Their movements are voluntary. They are also responsible for holding the bones of the skeleton together and giving shape to our body.

2. Heart or cardiac muscles: These muscles bring about the contraction and relaxation (beating) of the heart. Their movement is involuntary. Cardiac muscles cause our heart to relax and contract continuously at a rate of about 70 times per minute.

3. Smooth muscles: These muscles are present in the internal organs other than the heart. For example, muscles of the stomach, intestine, blood vessels, uterus, etc. Their movements are involuntary and slow. Various vital functions of our body, of which we remain quite unaware, are carried out by these special muscles.

Teacher's Note

Your heart is a muscle that never stops working. It beats even when you sleep. In India, many children do yoga which makes their muscles strong and healthy.

Exam Trick

Remember: Skeletal muscles = voluntary (you control them). Cardiac and smooth muscles = involuntary (automatic, you cannot control them).

Points to Remember

Skeletal muscles are attached to bones.
Cardiac muscles make the heart beat.
Smooth muscles work automatically inside organs.
Voluntary muscles work by your will.
Involuntary muscles work automatically.

How do muscles perform their functions?

1. Hold your arm straight at the elbow (i.e.180°) without closing your fist.

2. Bend the arm at the elbow through 90°.

3. Touch the shoulder with your fingers on same side.

Muscles of which part of your arm contracted and relaxed during the above three actions?

Muscles in our body always work in groups. When some muscles contract, other muscles of the same group relax. This is how muscles help in the proper performance of the various functions of our body.

The muscle on the front of the bone in our upper arm is called the biceps. The muscle at the back is called the triceps.

What would happen if:

1. The cardiac muscles do not move.

2. Food enters the stomach and the stomach muscles do not move.

Always remember –

Muscles of our body must be strong and efficient. Our diet must include proteins and carbohydrates in sufficient quantity for the proper growth and repair of muscles. We must get regular exercise. It makes the muscles strong. We must sit with a straight back, and not with the back hunched or bent. Otherwise, gradually, changes occur in the structure of the vertebrae. Muscles in the shoulder and back begin to hurt. Disorders of the vertebral column may also arise.

During exercise, movements of the heart muscles become more rapid. Breathing, too, becomes faster, ensuring a sufficient supply of oxygen and nutrients to various parts of the body.

Teacher's Note

Good posture is very important. When you sit hunched, your back gets hurt. In Indian schools, teachers always tell students to sit straight during class.

Exam Trick

Remember: Strong muscles need protein. Just like a plant needs water to grow, your muscles need protein to grow strong.

Points to Remember

Muscles need proteins and carbohydrates to grow.
Regular exercise makes muscles strong.
Always sit with a straight back.
Bad posture can hurt your spine.
During exercise, heart rate and breathing increase.

Digestive System

1. What happens to the food we eat, inside our body?

2. Does this food mix as it is with the blood?

Conversion of food into a soluble form and its absorption into the blood is called digestion.

The digestive system consists of the alimentary canal and digestive glands. The total length of alimentary canal is about 9 metres. Its main parts are the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus. The salivary glands, liver and pancreas are the digestive glands connected to the alimentary canal.

Different organs of the digestive system systematically perform the function of digestion. There are different stages in the process of digestion of food and at each stage there is a different organ of the digestive system which performs its specific role. Let us study the structure and function of each organ of the digestive system.

Teeth

The process of digestion begins with the function of the teeth in the mouth. There are four types of teeth, namely, incisors, canines, pre-molars and molars. Each type of tooth has a specific function. Each tooth is covered by a hard substance called enamel. Enamel is made of a calcium salt.

Saliva contains an enzyme called ptyalin or salivary amylase. Ptyalin converts starch into a sugar called maltose.

During digestion, does all the food that we have eaten get converted into useful, nutritive substances?

Collect information about the various organ-systems from the websites www.livescience.com and www.innerbody.com

Learn a new word

Enzymes are substances secreted in the body of an organism, which bring about specific chemical reactions. They act as catalysts. Digestive enzymes of the digestive system bring about changes in the food materials. Metabolic processes are impossible without enzymes. Enzymes are a specific type of proteins. They are most active at normal body temperature.

Teacher's Note

Enzymes are like workers in a factory. Each worker has one job. Ptyalin breaks starch, pepsin breaks protein. This is how our body digests food step by step.

Exam Trick

Remember: Enzymes = biological catalysts. They speed up digestion. Without them, digestion would be very slow.

Points to Remember

There are four types of teeth: incisors, canines, pre-molars, molars.
Enamel is the hard coating on teeth.
Ptyalin is an enzyme in saliva.
Ptyalin converts starch into maltose.
Enzymes speed up chemical reactions in digestion.

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