Muscles and their working
When you blink, smile, lift a school bag or run for a bus, you use muscles. Even when you sit still, small muscles keep your back straight and your eyes steady.
Muscles (स्नायू) are bundles of fibres that can contract and relax as required. They are attached to bones by tendons (कंडरा).
In the figure : In the figure muscles work in groups. To bend the arm (Q) the muscle in front (A, biceps) contracts and the muscle at the back (B, triceps) relaxes; to straighten it (P) the opposite happens. C is a tendon, which joins the muscle to the bone.
Muscles and their working
In the app you can move this figure with your finger.
Open in the appRule 1: How muscles work — When muscles contract there is movement at the joint, and the bones move nearer to or away from each other. Muscles are needed for all movements, from small eyelid movements to chopping wood. They give the body its shape and posture.
- Easy : Biceps contracts → the arm bends.
- Medium : Triceps contracts → the arm straightens, while the biceps relaxes.
- Exam-type : Lifting a bucket with a bent arm: the biceps contracts and the triceps relaxes.
In the figure : In the figure muscles make almost 40% of the weight of a healthy adult (40 out of 100).
Rule 2: Facts about muscles — There are more than 600 muscles in the human body, about 40% of a healthy adult's weight. About 30 muscles in the face show happiness, sadness and fear. The study of muscles is myology. The largest muscle is in the thigh; the smallest is attached to the ear bone stapes.
- Easy : 40% of 50 kg = 20 kg of muscle.
- Medium : 40% of 70 kg = 70 × 40 ÷ 100 = 28 kg.
- Exam-type : If an adult's muscles weigh 24 kg, her body weight is 24 × 100 ÷ 40 = 60 kg.
Muscles pull; they cannot push. They work in pairs, one contracts and the other relaxes.
Thinking tendons and muscles are the same. Tendons join muscles to bones.
Memory clue: "Biceps Bends, Triceps Tightens-to-straighten" (B for Bend).
Spot the difference
| Point | Biceps | Triceps |
|---|---|---|
| Position | Front of upper arm | Back of upper arm |
| Contracts to | Bend the arm | Straighten the arm |
Practice questions
- 1What are tendons?
- 2What are muscles made of?
- 3About what percentage of an adult's weight is muscle?
- 4What is the study of muscles called?
- 5Which muscle contracts to bend the arm?
- 6Find the weight of muscles in a 70 kg adult.
- 7An adult's muscles weigh 24 kg. Find the body weight.
- 8Why can the arm not be straightened if the triceps cannot contract?
Show answers (try them yourself first)
- 1Structures that join muscles to bones.
- 2Bundles of fibres.
- 3About 40%
- 4Myology
- 5Biceps
- 670 × 40 ÷ 100 = 28 kg
- 724 × 100 ÷ 40 = 60 kg
- 8Muscles work in pairs; the triceps contracts to straighten the arm while the biceps relaxes.
Types of muscles
You decide to lift your hand and it lifts. But you do not decide to make your heart beat, or your food move down. Some muscles obey us; some work on their own.
Voluntary muscles (ऐच्छिक स्नायू) work by our will. Involuntary muscles (अनैच्छिक स्नायू) work without our will.
In the figure : In the figure P: skeletal muscles (attached to two bones, voluntary). Q: cardiac muscles (the heart, involuntary, about 70 beats per minute). R: smooth muscles (hollow organs such as the stomach and intestine, involuntary).
Rule 1: Three kinds of muscles — Skeletal muscles: both ends attached to two different bones (arms, legs); voluntary; hold the skeleton together and shape the body. Cardiac muscles: make the heart contract and relax about 70 times per minute; involuntary. Smooth muscles: in internal organs other than the heart (stomach, intestine, blood vessels, uterus); involuntary and slow.
- Easy : Arm and leg muscles: skeletal and voluntary.
- Medium : The heart beats about 70 times per minute: in 10 minutes about 70 × 10 = 700 beats.
- Exam-type : In one hour the heart beats about 70 × 60 = 4200 times, and in a day about 4200 × 24 = 100,800 times.
In the figure : In the figure voluntary muscles work according to our will (arms, legs, chewing); involuntary muscles do not (heart, stomach, intestine).
Rule 2: Voluntary and involuntary — Involuntary muscles do not depend on our will: breathing, blood circulation and digestion. Muscles work in groups; when some contract, others of the group relax. For strong muscles we need proteins and carbohydrates, regular exercise and a straight sitting posture.
- Easy : Chewing is voluntary.
- Medium : Digestion in the stomach is involuntary and slow.
- Exam-type : You can stop lifting your arm when you wish, but you cannot stop your heart by wishing.
Skeletal = voluntary. Cardiac and smooth = involuntary.
Thinking the heart muscle is smooth muscle. It is a separate type: cardiac.
Memory clue: "Skeletal = Self-controlled (Skeleton)"; cardiac and smooth work on their own.
Spot the difference
| Type | Where | Control |
|---|---|---|
| Skeletal | Arms, legs | Voluntary |
| Cardiac | Heart | Involuntary |
| Smooth | Stomach, intestine, blood vessels | Involuntary |
Practice questions
- 1What are voluntary muscles?
- 2Name the three types of muscles.
- 3Which muscles make the heart beat?
- 4About how many times does the heart beat in a minute?
- 5Name two organs with smooth muscles.
- 6How many times does the heart beat in 10 minutes at 70 beats per minute?
- 7How many times does the heart beat in an hour?
- 8Classify as voluntary or involuntary: chewing, breathing, writing, digestion.
Show answers (try them yourself first)
- 1Muscles that work according to our will.
- 2Skeletal, cardiac and smooth.
- 3Cardiac muscles
- 4About 70
- 5Stomach and intestine.
- 670 × 10 = 700
- 770 × 60 = 4200
- 8Voluntary: chewing, writing. Involuntary: breathing, digestion.
Digestive system, teeth and enzymes
When you chew a piece of roti for a long time, it starts to taste slightly sweet. Your saliva has already started changing the starch into sugar. Digestion begins even before you swallow.
Digestion (पचन) is the conversion of food into a soluble form and its absorption into the blood. Enzymes (विकरे) are substances that bring about specific chemical reactions in the body.
In the figure : In the figure of the alimentary canal and the digestive glands: A oesophagus, B stomach, C liver, D pancreas, E small intestine and F large intestine.
Rule 1: Digestive system — The alimentary canal is about 9 m long: mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus. Digestive glands: salivary glands, liver and pancreas.
- Easy : Food path: mouth → oesophagus → stomach.
- Medium : Food path: stomach → small intestine → large intestine → anus.
- Exam-type : Glands that add juices: salivary glands (mouth), liver (bile) and pancreas (pancreatic juice).
In the figure : In the figure the four types of teeth: A incisors, B canines, C pre-molars and D molars.
Rule 2: Teeth and saliva — Digestion starts in the mouth with the teeth. The four types of teeth are incisors, canines, pre-molars and molars. Each tooth is covered by enamel, made of a calcium salt. Saliva has the enzyme ptyalin (salivary amylase), which converts starch into maltose.
- Easy : Incisors cut the food.
- Medium : Molars grind the food; ptyalin turns starch into maltose.
- Exam-type : Enamel protects the teeth, so we should brush them regularly.
In the figure : In the figure a sketch shows that enzymes are most active at normal body temperature (about 37 °C, B) and much less active at much lower or higher temperatures.
Rule 3: Enzymes — Enzymes are secreted in the body and act as catalysts. They are a type of protein and are most active at normal body temperature.
- Easy : Enzymes work best at about 37 °C.
- Medium : Very high or very low temperature makes enzymes much less active.
- Exam-type : Each enzyme brings about a specific reaction, like a key opening one lock.
Digestive system, teeth and enzymes
In the app you can move this figure with your finger.
Open in the appDigestion begins in the mouth. Ptyalin changes starch to maltose.
Thinking digestion starts in the stomach. It starts in the mouth.
Memory clue: "I Can Prepare Meals": Incisors, Canines, Pre-molars, Molars (front to back).
Spot the difference
| Teeth | Job |
|---|---|
| Incisors | Cut |
| Canines | Tear |
| Pre-molars and molars | Grind |
Practice questions
- 1What is digestion?
- 2How long is the alimentary canal?
- 3Name the digestive glands.
- 4Name the four types of teeth.
- 5What covers a tooth?
- 6What does ptyalin do?
- 7Why does a chewed roti taste sweet after some time?
- 8Why do enzymes work poorly when a person has a very high fever or is very cold?
Show answers (try them yourself first)
- 1Conversion of food into a soluble form and its absorption into the blood.
- 2About 9 m
- 3Salivary glands, liver and pancreas.
- 4Incisors, canines, pre-molars and molars.
- 5Enamel (a calcium salt).
- 6Converts starch into maltose.
- 7Ptyalin in saliva changes starch into maltose, a sugar.
- 8Enzymes are most active at normal body temperature, and much less active at much higher or lower temperatures.
Organs of the alimentary canal
A bag of rice goes in the sack at the shop, but the cook gets the cooked rice on the plate. In the same way, food goes through several "rooms", each doing a job, till only what the body can use enters the blood.
The stomach (जठर) churns food and starts protein digestion; the small intestine (लहान आतडे) is where most digestion and absorption take place.
In the figure : In the figure the alimentary canal is about 9 m long: the small intestine is about 6 m and the large intestine about 1.5 m.
Rule 1: Stomach and glands — The oesophagus pushes food to the stomach. The stomach secretes gastric juice (hydrochloric acid, pepsin, mucus); food is churned into a semi-solid slurry and mainly proteins are digested. The liver is the largest gland and stores glucose; the gall bladder stores bile, which helps in the digestion of fats. The pancreas secretes pancreatic juice with enzymes.
- Easy : The liver is the largest gland.
- Medium : The gall bladder stores bile, which helps fat digestion.
- Exam-type : Mainly proteins are digested in the stomach, and the mucus protects the stomach wall from the acid.
In the figure : In the figure of the stomach: food comes from the oesophagus (A); mucus protects the inner lining (B); the food is churned into a semi-solid slurry (C), which passes on to the small intestine (D).
Organs of the alimentary canal
In the app you can move this figure with your finger.
Open in the appRule 2: Intestines — The small intestine (about 6 m) is where most digestion and absorption take place. The large intestine (about 1.5 m) absorbs only water. The appendix is attached to its first part, and undigested material is thrown out through the anus.
- Easy : The small intestine absorbs digested food.
- Medium : The large intestine absorbs only water.
- Exam-type : Small + large intestine = 6 + 1.5 = 7.5 m, which leaves 9 − 7.5 = 1.5 m for the rest of the canal.
Stomach: proteins. Liver: bile for fats. Small intestine: most digestion and absorption. Large intestine: water.
Thinking the large intestine does most of the digestion. It only absorbs water.
Memory clue: Small intestine = long but narrow (6 m); large intestine = short but wide (1.5 m).
Spot the difference
| Organ | Length or role |
|---|---|
| Stomach | Churns food, digests proteins |
| Small intestine | About 6 m; most digestion and absorption |
| Large intestine | About 1.5 m; absorbs water |
Practice questions
- 1What does the oesophagus do?
- 2Name the components of gastric juice.
- 3Which is the largest gland?
- 4What does the gall bladder store?
- 5Where does most digestion and absorption take place?
- 6What does the large intestine absorb?
- 7Small intestine is 6 m and large intestine is 1.5 m. What length of the 9 m canal is left for other organs?
- 8Why does the stomach wall not get damaged by hydrochloric acid?
Show answers (try them yourself first)
- 1Pushes food to the stomach.
- 2Hydrochloric acid, pepsin and mucus.
- 3Liver
- 4Bile
- 5In the small intestine.
- 6Only water.
- 79 − (6 + 1.5) = 1.5 m
- 8Mucus protects the inner lining.
Digestive juices and harmful habits
If you eat a ghee-laden pakoda, bile helps break the fat into tiny drops so that it can be digested. Each food type has its own digestive juice, like each lock having its own key.
Digestive juices (पाचक रस) are fluids secreted by glands that act on food in different parts of the canal.
In the figure : In the figure the digestive juices act on: ptyalin on starch, pepsin on proteins, bile on fats, amylase on carbohydrates and lipase on fats.
Rule 1: Digestive juices — Hydrochloric acid makes food acidic; pepsin breaks down proteins; mucus protects the stomach lining. Bile makes food alkaline and emulsifies fats. Pancreatic juice: trypsin (proteins to amino acids), lipase (fats to fatty acids and glycerol), amylase (complex carbohydrates to simple sugars). Intestinal juice acts on proteins, carbohydrates and fats.
- Easy : Pepsin acts on proteins.
- Medium : Lipase breaks fats into fatty acids and glycerol.
- Exam-type : Trypsin → proteins to amino acids; amylase → complex carbohydrates to simple sugars; bile → makes food alkaline and emulsifies fats.
In the figure : In the figure 7th April is World Health Day (P) and 31st May is World No Tobacco Day (Q).
Rule 2: Harmful habits — Tobacco, smoking and alcohol harm health. Tobacco causes vomiting, nausea and headache, injures teeth, gums and the mouth, inflames the pharynx and intestine and may lead to cancer. 31st May is World No Tobacco Day and 7th April is World Health Day.
- Easy : Tobacco injures the teeth, gums and mouth.
- Medium : Tobacco may lead to cancer.
- Exam-type : 7 April to 31 May: 23 days left in April + 31 days of May = 54 days.
Ptyalin: starch. Pepsin: proteins. Bile: fats. Lipase: fats. Amylase: carbohydrates. Trypsin: proteins.
Thinking bile contains enzymes. Bile only emulsifies fats; the enzymes are in other juices.
Memory clue: Pepsin–Protein (P–P); Lipase–Lipid (L–L); Amylase–starch.
Spot the difference
| Juice or enzyme | Acts on |
|---|---|
| Ptyalin, amylase | Starch or carbohydrates |
| Pepsin, trypsin | Proteins |
| Lipase, bile | Fats |
Practice questions
- 1What does hydrochloric acid do in the stomach?
- 2Which enzyme digests proteins in the stomach?
- 3What does bile do?
- 4What does lipase break fats into?
- 5What does trypsin convert proteins into?
- 6Which two dates are mentioned for health awareness?
- 7How many days are there from 7 April to 31 May?
- 8Name two harmful effects of tobacco and say why it should be avoided.
Show answers (try them yourself first)
- 1Makes the food acidic.
- 2Pepsin
- 3Makes food alkaline and emulsifies fats.
- 4Fatty acids and glycerol.
- 5Amino acids
- 67th April (World Health Day) and 31st May (World No Tobacco Day).
- 723 + 31 = 54 days
- 8It injures teeth, gums and the mouth and may lead to cancer, so it should be avoided.
Quick revision
- Skeletal muscles are voluntary; cardiac and smooth muscles are involuntary.
- Digestion starts in the mouth; most digestion and absorption occurs in the small intestine.
- Bile (liver) digests fats; pepsin digests proteins; ptyalin digests starch.