Human Body Encyclopedia
Language: English
HumanBody Encyclopedia
A DORLING KINDERSLEY BOOK
Contents Human body 4-5 Your amazing body 6-7 What makes you you? 8-9 Building blocks 10-11 Organizing the body Skeleton and bones 12-13 Skeleton 14-15 Head case 16-17 Bendy backbone 18-19 Living bone 20-21 Bone and cartilage 22-23 Moving joints Moving muscles 24-25 The body’s muscles 26-27 How muscles work 28-29 Muscle power Brain and senses 30-31 Headquarters 32-33 Network of nerves 34-35 Touchy feely 36-37 Taste and smell 38-39 Look out! 40-41 How we see 42-43 Eye to brain 44-45 Listen here 46-47 Balancing act Senior editor Penny Smith Senior art editor Cheryl Telfer Editors Ben Morgan, Zahavit Shalev Additional design Jacqueline Gooden, Tory Gordon-Harris, Claire Patane, Laura Roberts Illustrator Peter Bull Digital illustrator Pilar Morales Consultants Dr Penny Preston, DrFrances Williams Publishing manager Sue Leonard Managing art editor Clare Shedden Jacket design Victoria Harvey Picture researchers Marie Ortu, Rob Nunn Production controller Shivani Pandey DTP designer Almudena Díaz First published in Great Britain in 2005 by Dorling Kindersley Limited 80 Strand, London WC2R 0RL A Penguin Company 2 4 6 8 10 9 7 5 3 1 Copyright © 2005 Dorling Kindersley Limited, London All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. A catalogue record for this book is available from the British Library. ISBN 1-4053-0848-6 Colour reproduction by Colourscan, Singapore Printed and bound in China by Toppan Discover more at www.dk.com LONDON, NEW YORK, MUNICH, MELBOURNE, and DELHI 2 Test yourself with the questions at the bottom of each page...
3. 3. Heart and blood 48-49 Blood flow 50-51 Boom boom 52-53 All about blood 54-55 Blood cells 56-57 Bumps and cuts 58-59 Hormones Lungs and breathing 60-61 Air bags 62-63 Air and oxygen 64-65 Making sounds 66-67 Ah-choo! Skin, nails, and hair 68-69 All wrapped up 70-71 At your fingertips 72-73 Fairly hairy Fighting disease 74-75 Germs 76-77 Body defences 78-79 Fighting germs 80-81 Allergies Digestive system 82-83 Digestive system 84-85 Chew it over 86-87 From mouth to stomach 88-89 Inside the intestines Urinary system 90-91 Waterworks 92-93 The stretchy bladder About this book This book has special features that will show you how to get your hands on as much information as possible! Use the “become an expert” buttons to find out more about a subject on other pages. 3Youwillalwaysfindtheanswershere! Try putting sugar on different places on your tongue. It tastes sweeter in some places than others. Now try salt, lemon juice, and coffee. get into it Runny nose When you have a cold, tiny hairs in your nose get clogged with mucus. This stops them wafting smell particles deep into your nose and makes it difficult to smell – and taste – things. We need to eat and drink to survive, but taste and smell are what make these everyday activities so enjoyable. Taste and smell Taste detector Your tongue is a big muscle covered in clusters of taste buds. Each cluster recognizes a particular kind of taste. Sweet Salt Salt Bitter Sour Taste buds Saliva in your mouth dissolves your food. The food washes over tiny taste buds between the bumps on your tongue. Taste buds recognize different flavours. Sour S ome noses can recogniz e10,000differentsme lls. Bitter foods, such as coffee can be bad for you. Most poisons are bitter. Sour foods include lemon and vinegar. Food that has “gone off” tastes sour. Salt detecting taste buds can be found on the lips as well as on the tongue. Sweet foods naturally attract us. Our first food – milk – is sweet. 36 37 How much saliva does an average person produce in a day? 1000-1500millilitres. Brain and senses Taste and smell Different tastes There are five types of tastes – bitter, sour, salty, sweet, and umami. Umami is the savoury taste of foods like soy sauce and mushrooms. Smell receptors Special cells deep inside your nose recognize scent particles floating in the air. These cells link directly to your brain. Sensitive nose Much of what we think of as taste is actually smell. The back of your nose is linked to your mouth so you can smell your food as you chew it. 10,000taste buds are crammed onto your to ngue. Your nose and mouth are linked at the throat. Coloured discs contain facts about special topics, such as taste. Circles show close-up images you might not otherwise be able to see. Reproduction and growth 94-95 Making a baby 96-97 Growing in the womb 98-99 Double trouble Life cycle 100-101 The early years 102-103 Growing up 104-105 Growing older Keeping healthy 106-107 What’s in food? 108-109 Sleep 110-111 Doctors and dentists Communication 112-113 Body language 114-115 Use your hands 116-117 Express yourself Reference section 118-119 Amazing facts about YOU! 120-121 Through the ages 122-123 Glossary 124-127 Index 128 Acknowledgements Reproduction and growth 94-95 Making a baby 96-97 Growing in the womb 98-99 Double trouble Life cycle 100-101 The early years 102-103 Growing up 104-105 Growing older Keeping healthy 106-107 What’s in food? 108-109 Sleep 110-111 Doctors and dentists Communication 112-113 Body language 114-115 Use your hands 116-117 Express yourself Reference section 118-119 Amazing facts about YOU! 120-121 Through the ages 122-123 Glossary 124-127 Index 128 Acknowledgements “Get into it” activity buttons show you how you can try things out for yourself.
4. 4. 4 The greatest machine you’ll ever own is your body. It’s more complicated than any computer, it lasts for a lifetime, and it’s yours for free. Body parts Your body is made up of hundreds of different parts. You probably know the names of the bits you can see, but there are many more hidden deep inside you. What do we call the study of the human body? Inside your body Doctors can see inside your body with special cameras. X-ray cameras take pictures of hard body parts like bones. Other cameras, called scanners, can see soft body parts. Two of everything Body parts often come in pairs. You have two feet, two eyes, two ears, two lungs, and so on. This means you have a handy spare in case one of them gets damaged. Human body Your amazing body Cheeks Lips Nose Teeth Eyebrows Eyes Forehead W rists Fingers Hair A chest X-ray shows the bones in your chest. The white shape in the middle is the heart. Ears H ands Become an expert... on the skeleton, pages 12-13 on digestion, pages 82-83
5. 5. 5 Being human Although we look different to animals, our bodies are similar on the inside. Our closest animal relatives are chimpanzees. Water, water Water is the most important chemical in your body. About two-thirds of your weight is water. No substitute The human body is too complicated for robots to copy. Robots can copy the way we walk, but they can’t think or feel like we do. Carbon is the chemical in diamonds and coal. A fifth of you is carbon. Your amazing body Iron makes your blood red. You have enough to make one small iron nail. Phosphorus is in the tips of matches, as well as your bones and teeth. Sodium and chlorine make salt. Blood is one- third as salty as sea water. Potassium is used in some types of soap. It’s also in your body fluids. Robot Curiosity quiz Take a look at the first few pages in this book and see if you can find these pictures. The ingredients Your body is made of just a few simple chemicals, plus water. Chimps have hands like ours. Chimpanzee Compared to chimps, our bodies look almost hairless. Anatomy. Nitrogen is important in muscles. It’s also the main ingredient in air.
6. 6. 6 All human bodies work the same way, but everyone is different. Nobody looks, sounds, or thinks exactly like you. You’re different because of the way your genes and experience shape you as you grow up. How many genes are there in the human body? Curly hair Green eyes Freckles Human body What makes you you? Unique The shape of your face, the colour of your hair, and many other things make you unique – different from everyone else. Black hair Fair skin
7. 7. 7 DNA Your genes are stored in a chemical called DNA, which looks like a twisted ladder with four different types of rung. The rungs make up a four-letter alphabet that spells out your genes, like letters in a book. In the genes Genes are instructions that build your body and tell it how to work. Your genes control many of the things that make you unique, like the colour of your eyes or how tall you’ll be. Changing body Genes don’t control everything – experience also shapes you. If you exercise a lot, for instance, your body gets stronger. About30,000. What makes you you? This girl has a gene that allows her to roll up her tongue. The boy doesn’t have the gene, so he can’t roll his tongue. DNA can split and copy itself. Learning to ride a bike changes your brain and your body. Look in a mirror and see if you can roll your tongue. Don’t cheat by squeezing it with your lips. Test your family to see who has the gene. get into it In the family Your genes came from your parents. Half come from your mother and half come from your father. If you look like your parents, it’s because you share the same genes. There’s e nough DNA inside you to stretc h to the Suna nd back 400 tim es.
8. 8. 8 Every part of your body is made of tiny building blocks called cells, which fit together like bricks in a wall. Cells are so small that hundreds could fit on the point of a pin. How many cells are there in the human body? Making new cells A cell makes new cells by dividing. The two new cells are half the size, but they soon grow back. Millions of your cells die every second, but millions of others divide to replace them. The skin on your fingertips is made of lots of small ridges. Human body Building blocks The nucleus controls the rest of the cell. Tiny generators provide cells with power. The outer skin, or membrane, stops things leaking out. Inside a cell In the middle of a cell is its control centre – the nucleus. The nucleus sends instructions to the rest of the cell, telling the cell what chemicals to make. The new cells pull apart and separate, but they usually stay close neighbours. Before a cell divides, the nucleus splits to make two nuclei. DNA is stored in the cell nucleus. D NA The inside of a cell is packed with a kind of living jelly called cytoplasm.
9. 9. Cells make tissue Your body contains hundreds of different types of cells that do different jobs. Cells of the same type usually group together to form tissue. Fat, muscle, bone, and nerves are types of tissue. Blood is a liquid tissue. Building blocks 9About100trillion. How big are cells? Cells are too small to see with the naked eye, but scientists can photograph them through powerful microscopes. The cells on your skin are about a hundredth of a millimetre wide. Fat cells are bubble shaped. They store fat under your skin. Many blood cells are red. They carry oxygen around the body. Nerve cells are thin and wiry. They carry electrical signals. Bone cells make your bones hard. They live in tiny holes in bones. The cells on the surface of your skin are tough and flat. They overlap to form layer of armour that protects the softer cells below. A microscope can zoom in to see the tiny, flaky cells on the ridges of a person’s fingerprint. More than 2000 dead skin cells f elloffyouwhileyoureadthissentence.
10. 10. Your cells and tissues are organized into larger body parts called organs. In turn, your organs work together to form body systems. Organ transplant If a vital organ stops working, doctors may replace it with an organ from another person. This is called a transplant. Organs An organ is a body part that does a specific job. Your heart’s job, for instance is to pump blood. Kidneys clean blood. The tubes that carry blood away from the heart are called arteries (shown in red). Heart Kidney Brain Human body Organizing the body Systems Organs and tissues work in teams to carry out major tasks, like transporting blood or processing food. These teams are called systems. The heart is the largest organ in the blood system. It pumps blood around the body. 10 Heart and blood Your heart, blood, and blood vessels make up the blood system. It transports vital supplies around your body. The tubes that carry blood back to the heart are called veins (shown in blue). Which body system makes your stomach rumble?
11. 11. Thedigestivesystem. 11 Nerves Your nervous system carries electrical signals around your body. You need this system to see, hear, think, and react. A long, twisting tube makes up your intestines, where digested food is absorbed. Senses, such as touch, rely on nerve cells that send signals to your brain. Muscles change the position of your skeleton by pulling different bones. Signals shoot along nerves to muscles, telling them when to pull. Organizing the body Breathing system: the main organs are your lungs, which take in air. Hormone system: this uses powerful chemicals to control your body and mood. Skin, hair, and nails: these form your body’s protective covering. Immune system: this seeks and destroys germs that get into your body. Urinary system: this cleans blood and gets rid of waste chemicals. Reproductive system: these are the organs that make babies. Other systems Some of your other important systems are shown in this list. Digestive system Your digestive organs break down food to provide your body with energy and raw materials. Muscles Your muscle system is made of tissues that move parts of your body by pulling on them or squeezing them. Your biggest muscles all pull on bones. Skeleton Bones and joints make up the skeletal system, an inner frame that supports the body. Your fingers are moved by muscles in your arm. The most powerful muscles are in your legs. A quarter of your bones are in your feet. Your brain is the nervous system’s control centre. Your mouth is the first part of the digestive system.
12. 12. 12 Your bones all join up to make a frame for your body called the skeleton. This protects your insides, and helps you move about. Skeleton Skeleton Howmanyribshaveyougot?24,unlessyouareoneoftherarepeoplebornwith26.13 Neck bones Did you know that you have seven bones in your neck, the same number as a giraffe? The top one allows you to move your head up and down, the second lets you rotate it from side to side. Smallest bone Around the same length as a grain of rice, this is one of the smallest bones in your body. It lies deep inside your ear. Long lasting Bone is a very hard material and one of the last parts to rot away when a body is buried. This woman lived in the Stone Age, 5000 years ago, but her bones have survived until today. 206 bones There are 206 bones in an adult skeleton. Over half of these are found in the hands and feet – the parts of your body that perform the most complicated movements. Each finger has three bones, except for your thumb, which has two. There are 54 bones in your hands, and 52 in your feet. Your tail bone is at the very bottom of your spine. Thigh bone Shin bone Rib There are 24 bones in your spine. You have eight small bones in each wrist. Pelvis Frogs have very short spines to withstand the strain of the huge leaps they take. Snakes are incredibly bendy thanks to many identical vertebrae forming their long spines. Thethighboneisthebiggestandstrongestinthebody. Your ankle has three larger bones and four smaller ones. Skull Other skeletons Most animals have a backbone and are called “vertebrates”. Animals with no spine, like spiders and bugs, are called “invertebrates”. A fish’s spine allows it to bend its body from side to side so it can swim smoothly. Shoulder blade Jaw bone A giraffe’s long neck helps it to eat leaves off tall trees. Skeletonandbones Become an expert... on bone and cartilage, pages 20-21 on teeth, pages 84-85
13. 13. Label Skeleton and bones The most complex part of the skeleton is the skull. It is made of many bones that fit together tightly, to protect the brain and support the face. Head case Facial features This image shows the relationship between your skull and face. There are no bones shaping the front part of your nose, your lips, or your ears. Your nose and ears are shaped by cartilage. Why does a baby have spaces between its cranial bones? The cranium is the domed part of your sk ull. The frontal bone forms your forehead. Teeth are set into the upper and lower jaws. Helmet The upper part of the skull is like a helmet that protects the brain. The lower part forms a structure for your facial features to attach to. 14 The front of the nose has no bones. Eye sockets are made up of seven different bones. The brain fills most of the cranium.
14. 14. Soitsheadcouldwithstandbeingsquashedwhileitwasbeingborn. Head case Jigsaw The skull bones fit together like the pieces of a jigsaw. All but one of the bones are locked in place. This makes the skull very strong. Face from the past Scientists can work out what a dead person’s face looked like from their skull alone. They examine the facial bones and build up artificial cartilage, muscle, and skin over them. Meet the relatives Chimpanzees and humans share a common ancestor. However, chimps have smaller brains than humans so their craniums are smaller. Chimps also have a large ridge above their eyes, and a jutting jaw. Hole in the head From underneath you can clearly see the big hole at the bottom of this skull. The spinal cord – which runs down your back – meets your brain here. There are two parts to the upper jaw. Upper jaw Bac k of the head The lower jaw is not shown here. Blood vessels pass through small holes in the skull. The spinal cord goes through a large hole in the skull. The lower jaw is hinged. It is the only skull bone that can move. 15
15. 15. 16 Your spine is a length of bones running down the back of your body. Without it you couldn’t hold up your head and body, or make any sort of movement. What is a slipped disc? Stack of bones Your spine contains 24 separate bones called vertebrae. At the bottom are nine more vertebrae. They are much smaller and are fused together. Skeleton and bones Bendy backbone Segments of the spine Each vertebra has a strong, stubby section that supports the weight of your body, and a hole for the spinal cord to pass through. Fr ontofspin e Backofspine Yourspinecurvesgently,abitliketheletter“s”. The spinal cord goes through this hole. The first seven bones are in your neck. They are known as the cervical vertebrae. The next 12 are called the thoracic vertebrae. The five lumbar vertebrae bear most of your weight. The fused bones of the sacrum and coccyx don’t allow much movement. The coccyx consists of four fused vertebrae. A straight back is actually quite curvy. The thoracic vertebrae form joints with the ribs. The five sacral vertebrae are fused together.
16. 16. Bend over. Gently feel the bones of your spine with your fingertips. Can you follow them from neck to waist? 17It’swhenoneofthepadsbetweenthevertebraegetsdamaged. Bendy backbone Shock absorbers You twist and bend your spine almost every time you move. Sandwiched between the vertebrae are pads of cartilage to stop them banging and rubbing against each other and getting worn out. Ribcage Your thoracic vertebrae connect to your ribs. Together they form a cage around your heart and lungs. Rib bones are curved. They are also thinner and more bendy than the bones in your spine. Bendy backbone The amount of movement between each vertebra and its neighbours is actually very small, but added together they allow for a large range of movement. A woman’s pelvis is shaped differently to a man’s. A baby can pass through it when she gives birth. The way the back curves means we can’t bend as far back as we can forwards. Pelvis Reproductive organs and some digestive organs rest in the bowl-shaped hollow of your pelvis. The sacral vertebrae and coccyx form the bottom of the bowl. Yo u could be this bendy...... ...withalotofpractice! Vertebra Pad of cartilage Space for spinal cord get into i t The pads give you a little bit of movement in all directions.
17. 17. 18 What are the most commonly broken bones? Skeleton and bones Their outer surface may be hard and dry but that doesn’t mean your bones aren’t alive. Bones are always growing and repairing themselves. Compact bone The hardest and most dense part of the bones is the outer layer. It is made of calcium, a substance we get from our food. Teeth are made of calcium too. What’s inside our bones? Bone accounts for one sixth of your body’s weight. Its clever structure means it’s often lighter than it looks. Living bone Bone marrow A jellyish substance called marrow fills the centre of many of your larger bones. It supplies your body with red blood cells at a rate of 3 million cells per second. Marrow can be found in the spine, skull, and the main leg and arm bones. Spongy bone Parts of some bones have a honeycomb structure with lots of spaces. This makes them weigh less than if they were solid right through.
18. 18. Living bone Curiosity quiz Take a look through the skeleton and bones pages and see if you can identify where these bony bits come from. If the broken bone ends have slipped apart they must be repositioned by a doctor before healing begins. Broken bone Bones are strong and flexible enough to cope with a lot of pressure, but, as this X-ray shows, they sometimes break. Luckily they can heal themselves. 19 Your b onesarestill growing unt ilyourlateteens. On the mend New cells form at each end of the broken bone, closing the gap between them. It takes about 6 weeks for this to happen. Looking after your bones Calcium from milk and cheese is needed to build strong bones. Weight-bearing exercise like walking, climbing, or skating helps to strengthen bones. Become an expert... on the skeleton, pages 12-13 on skin and nails, pages 70-71 Fingers,wrists,andarms. Padded clothes help protect bones from sudden impact.
19. 19. Bone and cartilage Stick out your ears! Your ears are made of cartilage, not bone. They are strong, but much more bendy than your bony bits. Cross-section of an ear – the cartilage sits between two layers of skin. When you were a baby, you were tiny. Slowly, as you get older and bigger, your bones do a clever trick. Not only do they grow, but they also change. More, less You’ve got more bones than your mum or dad! You were born with over 300 “soft” bones, but as you get older, many fuse together. By the time you’re 25 you’ll have 206 fully formed bones. Making bones Babies’ bones are made out of a soft and bendy material called cartilage. Slowly this hardens and turns into bone. 20 Which foods are rich in calcium, the mineral you need to grow healthy bones? Skeleton and bones Baby bones are entirely made of soft, growing cartilage. Adolescent bones are mostly bone, with a small amount of cartilage. Adult bones have stopped growing. Most no longer contain cartilage. Baby’s hand
20. 20. Bone shows up as purple in these X-rays. The difference between the amount of bone can clearly be seen. The pads of cartilage get squashed from standing up and stretch back out while you’re lying down. 21Milk,cheese,yogurtandice-cream. Smooth coated joints The ends of neighbouring bones are covered in smooth cartilage. That way, they can glide against each other when you move. Bone and cartilage Taller, shorter Between each bone in your spine are small disks of cartilage. During the day these get squashed, and when you rest at night they spread out again. This means you’re a little bit taller in the morning than in the evening. Cartilage coats the ends of these bones. Child’s hand Adult’s hand
21. 21. Fixed joints The bones that make up your skull start to join up soon after you are born. Once they have fused, none of them allow movement except the hinged jaw joint. What is tennis elbow? Skeleton and bones Have you ever used a joystick? That’s a ball and socket joint! Hinge joint Your knee can bend in the middle but it can’t swing from side to side. This joint has a hinge like the one that allows you to open and close a door. 22 Joints are the places where bones meet. Different kinds of joints allow you to move in different ways. Ball and socket Your hips are ball and socket joints. They allow you to move your legs in all directions and even to turn them. Knee joint Moving joints There are 19 moveable joints in your hand – not counting the ones in your wrist!
22. 22. Fabulously flexible People whose joints are particularly flexible are called “double- jointed”. The condition can run in families, but people who are double- jointed must practise if they want to keep their ligaments stretchy. Thenameforsoreelbowtendonscausedbyoveruse. Your elbows have a hinge joint for bending and a pivot joint so they can turn. Moving joints Hip hooray Joints, particularly knee and hip joints, sometimes wear out in old age. When this happens, doctors can remove the worn-out joint and replace it with an artificial one. 23 Bendy bits Different sorts of joints all over your body keep you moving. This woman has stretchy muscles and ligaments that allow her spine to bend further than most people can manage. Wrists have a joint that allows them to turn but not to go right round. Neck bones feature a pivot joint that allows your head to turn. Ligaments Bands of tissue called ligaments act like elastic. They hold your bones together yet still allow you to move. Thank your thumbs Your thumb is the most flexible of your fingers. You rely on your thumbs whenever you handle delicate objects. Tape your thumb to your first finger. See how difficult it is to open a notebook, pick up a pen, and write your name. get into it Your hand is a terrif icfeatofengineering! Ligament Bone Ankles contain different joints for up and down and side to side movement.
23. 23. Every time you move, you use muscles. Muscles make you walk, blink, and smile. Some muscles work without you thinking about them, but others need to be told to move. They all work by shrinking, which makes them pull or squeeze. Pulling strings About 650 of your muscles are wrapped around the bones of your skeleton. They move your body by pulling on the bones. Together they form the muscle system. Heart muscle When you put your hand on your chest, you can feel your heart beating. Your heart is a strong muscle that squeezes blood around your body. Smooth muscle This type of muscle makes things move inside your body. It mixes food in your stomach and pushes food through your intestines. The body’s muscles Moving muscles What weighs more: all your bones or all your muscles? The tibialis muscle bends your foot. Your longest muscle is the sartorius. It helps cross your legs. The biceps muscle bends your arm. Skeletal muscle cells are long and threadlike. Skeletal muscle Skeletal muscles pull on bones to change the shape of your skeleton and move your body. These muscles are voluntary, which means you can use thought to control them. Heart muscle cells are stripy with oval blobs. Smooth muscle cells are short with pointed ends. 24 The pectoralis muscle swings your arm.
24. 24. Tongue twister Your tongue is a bundle of lots of muscles that make it super flexible. It can reach anywhere in your mouth to pull and push bits of food. Its acrobatic movements are also vital to speech. Who’s in charge? You use hundreds of muscles when you run and jump. Your brain controls them all, a bit like a conductor controlling an orchestra. It sends signals along nerves to every muscle, saying exactly when to work and when to rest. Muscle magic Muscles have hundreds of uses. They make up about a third of your body weight. Fastest muscle: this one makes you blink. It works up to 5 times a second. Ear wiggling: a few people can control the muscles around their ears. Smile: a fake smile uses different muscles from a real, involuntary smile. 25Yourmuscles. The body’s muscles Become an expert ... on making sounds, pages 64-65 on how intestines push food, pages 88-89 Hundreds of muscles work in a carefully controlled sequence when you jump in the air. Your tongue contains at least 14 different muscles th at make it amazingly flexib le. Largest muscle: you use the muscle in your buttock for sitting and walking.
25. 25. Muscles work by contracting, which means they shorten. As a muscle contracts, it pulls. The larger the muscle, the more powerfully it pulls. Fibres in fibres Skeletal muscles are made of cells called muscle fibres. Inside these are even finer fibres called myofibrils, which contract to make a muscle shorten. When the triceps muscle contracts, it straightens your arm. Where is the body’s smallest muscle? Your forearm contains pairs of muscles that move your hand and fingers back and forth. When the bicep muscle contracts, it pulls your forearm and bends your arm. Bundle of muscle cells One muscle cell Moving muscles 26 How muscles work Myofibrils inside a muscle cell A typical muscle Working in pairs Muscles can pull but not push. They work in pairs that pull in opposite directions. When one muscle pulls, its partner relaxes.
26. 26. Tendons Muscles are fastened to bones by tough bands called tendons. When you wiggle your fingers, you can see the tendons move on the back of your hand. No rest Muscles work all the time. They hold you upright - without them you would flop on the floor. Muscles also work when you are asleep, keeping your body firm and toned. Making faces Muscles in your face are attached to skin as well as bone. They pull the skin when you change your expression. You use about 17 muscles when you smile. A floppy start A newborn baby has little control over his head or neck muscles. It takes about a month before it can hold up its head, and six months for strong, steady head control. Getting a stitch If you run a lot, you may get a pain in your side. This is a stitch. Scientists aren’t sure exactly why it happens but it might be because the muscles and ligaments in your abdomen are working too hard. 27Intheear. How muscles work Try raising your ring finger with your hand in this position. It’s stuck because it’s joined to the same tendon as the middle finger. Ring finger Middle finger
27. 27. The more you use your muscles,the better they get. Active games and exercise make your muscles larger, stronger, and more flexible. They also help you keep going without tiring. Flexibility When you’re flexible, your joints and muscles can move freely and your body can bend and straighten easily. Exercise that stretches your body, such as gymnastics or dancing, improves your flexibility. Muscle power Strength Pushing, pulling, and lifting make your muscles bigger and stronger. Bodybuilders lift heavy weights over and over again until their muscles are enormous. Stamina If you have stamina, you can keep going for a long time without getting tired. Exercise that makes you feel out of breath, like running, improves your stamina. 28 Moving muscles Become an expert ... on how your heart works, pages 50-51 on healthy food, pages 106-107 You need strong muscles to win a tug-of-war. What happens to muscles if you don’t exercise? This contortionist has made her body more flexible by doing exercises that stretch her back.
28. 28. Body heat This picture shows the heat of a man’s body. Muscles make heat when they work hard, which is why exercise makes you hot. On cold days, your muscles try to warm you up by shivering. Ways to keep fit Exercise is very good for your health. As well as making your muscles bigger, it strengthens your heart and lungs. Walking to school, or going out for walks, builds strength and stamina. Football is great for improving your flexibility and strength. Swimming strengthens your heart muscle and builds stamina. Cycling strengthens your leg muscles and builds up stamina. Muscle food To build strong muscles, you need a type of food called protein. Meat, fish, beans, milk, and eggs are rich in protein. 29Theygetsmallandweak. Muscle power Dancing keeps your body supple and helps build strength. Milk Egg Beans Chicken Fish Most vegetables don’t contain much protein. Fish is a very good source of protein.
29. 29. 30 Brain and senses The brain is the body’s control centre. It is a complicated organ that works very quickly, a bit like a brilliant, living computer. Muscle control Your cerebellum helps you to balance and move your muscles. You use this bit of your brain when you dance. Clever calculator The cerebrum is also responsible for thinking, speaking, and complicated tasks such as sums. Sense signals The cerebrum is the main part of your brain. It gets and stores sense information and also controls your movements. Your brain stem works at the same rate whether you’re awake or asleep. Does your brain hurt when you have a headache? Cerebrum Headquarters 24 hours a day Whatever else you do, the brain stem makes sure your heart and breathing never stop. Br ainstem Cerebellum
30. 30. 31No,yourbraincan’tfeelpainbutthemusclesaroundyourheadcan. Headquarters Curiosity quiz Take a look through the brain and senses pages and see if you can spot where these come from. 31 Short-term memory Your short-term memory only holds information for about a minute. You use it to compare prices when you go shopping, or to remember a name when you meet someone new. Learning When you learn to do something you create connections between cells in your brain. Next time you do it the connections are already there so it is easier. Brain box Your skull is a bony shell that fits together like a jigsaw around your brain. Shock- absorbing liquid fills the space between the brain and skull. Long-term memory Your name, phone numbers you know by heart, and skills such as riding a bike can be kept for many years in your long-term memory. In relation to the size of our bodies, humans have the biggest brains of any animal. Skull Brain
31. 31. No need to think You do some things without needing to think about them. These are called reflex actions and include blinking, coughing, and the knee-jerk reflex. Brain cells viewed through a microscope. Needing to urinate is a response to the message that your bladder is full. Itching is an irritating feeling. Your body reacts by making you scratch. Network of nerves Quick as a flash Nerve cells lie next to one another forming long chains. They pass messages to their neighbours – rather like a speedy relay race – to and from the brain. You’ve got 150,000 km (93,200 miles) of nerves in your body. Brain A good night’s sleep Your body and brain slow down when you sleep, but they don’t stop working. Your brain needs sleep to sort out the events of the previous day. Messages Your brain controls your body. It receives messages from all parts of your body and decides what to do. Pain gets a very quick response. You move away from what’s hurting you. Walking is the result of your brain telling your leg muscles to move. Hunger is your stomach telling your brain that it’s empty and you must eat. Blinking happens without you needing to think about it. Breathing is automatic too. It carries on even when you are asleep. Messagestravelfasterthanahigh-speedtrain. Pins and needles Sitting cross-legged for a long time squashes the nerves in your legs. When you stand up, the nerves start to work again, producing a tingling feeling. Cross your legs and tap just below the knee. BrainandsensesNetworkofnerves Whichisthelongestnerveinyourbody?Theonerunningfromyourbigtoetothebaseofyourspine.3332 All of the body contains nerve cells. These link up to form the network of nerves we call the nervous system. It transports messages between the body and the brain. Pain-killers When you get a filling, the dentist gives you an anaesthetic. This drug stops nerves passing on pain messages for a short time. Spinal cord – the centre of the network Your knee jumps forwards even though your brain hasn’t told it to move.
32. 32. Your skin is in immediate contact with the world. Using your sense of touch allows you to tell if something is hot or cold, dull or sharp, rough or smooth, or wet or dry. How many touch receptors are in a fingertip? Brain and senses Touchy feely Things we can feel Skin is packed with many sense receptors. Each sort responds to different sensations. 34 Ouch! The body has its own system of alarm bells. Pain receptors warn us when a part of the body has been hurt or is about to be harmed. This girl quickly moves her finger away from the thorn to stop the pain. It feels slimy!.... Merkel’s disk responds to light touch and is sensitive to the texture of things. Meissner’s corpuscle senses light touch. Warmth is detected by nerve endings quite close to the surface of the skin. Light touch sensors lie at the root of hairs on your arms and legs. Vibrations from an electric drill trigger vibration sensors. Tickly feelings result from a light and unexpected touch. Cold is felt by different sensors to heat. Extreme cold registers as pain. Deep touch sensors enable you to grip things tightly. Not worth noticing Although your brain receives messages all the time, it filters out the less important ones. That’s why you’re not constantly aware of the clothes against your skin. Sensitive fingertips full of receptors are able to tell coins apart.
33. 33. 35 Reading by touch Braille is a system that uses raised dots to represent letters and numbers. It was invented so that people with bad eyesight would be able to read by feeling the page with their fingertips instead of looking at words. About3,000.That’sroughlythesameasonthewholeofthetrunkofyourbody. Sensitive bits Skin contains more touch receptors than any other part of the body. But some areas are more sensitive than others. Fingertips are packed with sensors, especially light pressure receptors. Touchy feely Lips have very thin skin which is good at detecting heat and cold. Toes are very sensitive, but thick skin makes the heel less sensitive. get into it Put one finger in cold water, one in hot, then put both in warm water. The water feels cold to the hot-water finger and hot to the cold-water finger. Under the skin Dead cells form the surface of your skin. Below that lie sweat glands, hair follicles, and different types of sensory receptors. B I R D Braille was invented over 150 years ago. Surface of skin Free nerve endings respond to heat, cold, and pain. The Ruffini ending responds to firm or continuous touch. .... the message shoots off to the brain....Fat Dermis The Pacinian corpuscle responds to firm pressure and vibration.
34. 34. Try putting sugar on different places on your tongue. It tastes sweeter in some places than others. Now try salt, lemon juice, and coffee. get into it We need to eat and drink to survive, but taste and smell are what make these everyday activities so enjoyable. Taste and smell Taste detector Your tongue is a big muscle covered in clusters of taste buds. Each cluster recognizes a particular kind of taste. Sweet Salt Salt Bitter Sour Taste buds Saliva in your mouth dissolves your food. The food washes over tiny taste buds between the bumps on your tongue. Taste buds recognize different flavours. Sour Bitter foods, such as coffee can be bad for you. Most poisons are bitter. Sour foods include lemon and vinegar. Food that has “gone off” tastes sour. Salt detecting taste buds can be found on the lips as well as on the tongue. Sweet foods naturally attract us. Our first food – milk – is sweet. 36 How much saliva does an average person produce in a day? Brain and senses Different tastes There are five types of tastes – bitter, sour, salty, sweet, and umami. Umami is the savoury taste of foods like soy sauce and mushrooms. 10,000taste buds are crammed onto your to ngue.
35. 35. Runny nose When you have a cold, tiny hairs in your nose get clogged with mucus. This stops them wafting smell particles deep into your nose and makes it difficult to smell – and taste – things. S ome noses can recogniz e10,000differentsme lls. 371000-1500millilitres(35-53floz). Taste and smell Smell receptors Special cells deep inside your nose recognize scent particles floating in the air. These cells link directly to your brain. Sensitive nose Much of what we think of as taste is actually smell. The back of your nose is linked to your mouth so you can smell your food as you chew it. Your nose and mouth are linked at the throat.
36. 36. Sight is the body’s main sense and the main way we learn about our surroundings. Two-thirds of the information we take in comes from our eyes. Wandering eyes Six muscles control each eye. You use both eyes when you look at something, so your eyes move together. Look out! Iris 38 What is the sleep that collects in our eyes? Brain and senses Hidden away Most of your eye nestles safely in its socket and is protected by pads of fat. On the outside, you can see the iris, pupil, and some of the sclera. EyelidPupil Iris Pupil The middle of the eyeball is filled with fluid.The muscles surrounding your eyeball make precise movements so you can smoothly track moving objects. Sclera (or white of the eye) Atn ight,oureyescouldd etect a lighted candle 1.6km(1mile)away. Anirisisasun ique asafingerp rint Sclera
37. 37. Crying Tear glands behind your eyes produce drops of salty fluid. When you blink, your eyelids sweep this fluid over your eyes to keep them clean. If something gets into your eye, or you feel strong emotions, the drops turn into floods of tears. Eye colour The iris is the coloured part of the eye. All eye colours are produced by one substance, melanin. Lots of melanin results in brown eyes, less means a lighter shade. 39Dustandmucuswashedfromoureyesaswesleep. Look out! Either it’s dark or this person has seen something they like. Pupil size The pupil is the opening that controls how much light enters your eye. It’s smaller in bright light to protect the nerve cells in your eye, and bigger in dim light to let more light in. It also gets bigger when you see something or someone you like. Bone in your skull surrounds your brain and the backs of the eyes. Eyebrows sit above your eyes and prevent sweat dripping into them. Eyelids and lashes stop dust entering the eyes and then sweep it well away. Safekeeping Your eyes are fragile, squidgy balls made of watery jelly so they need to be well protected. Your pupils change size automatically. Tears drain into tear ducts. These link to your nose, which is why your nose runs when you cry. Tears are made behind each eyelid.
38. 38. Inside your eye is a lens like the lens of a camera. Its job is to focus light on the back of your eye so you can see things clearly. What is an eye specialist who tests eyesight called? Brain and senses How we see How your eye works Light from an object enters your eye through the pupil. It passes through the lens, and makes an upside down image on the retina at the back of your eye. Cells in your eye send messages down the optic nerve to your brain. Your brain flips the image back the right way round. Lightre flects off an object and enters your eye. Seeing in colour Your eyes contain millions of cells. Cone cells give you colour vision but don’t work well in dim light. Rod cells work well in dim light but see everything in shades of grey. The pupil is a hole that lets light into the eye. Optic nerve The lens is clear and flexible. It focuses on things by changing shape. The retina contains cells that sense light. An object The eye is filled with a semi-solid jelly. 40
39. 39. 41 Contact lenses These work like mini glasses and sit directly in front of the eye. They’re a bit fiddly, but once they’re in you can’t feel them at all. Anoptician. How we see Glasses bend the light entering your eye so it focuses on the retina. Colour blindness Some people cannot tell certain colours apart, especially red and green. This is called colour blindness. It is more common in men than women. Short eyeball If you have a short eyeball you will have difficulty seeing things close up. This is called long sightedness. Blurry vision Sometimes an eyeball is the wrong shape. The lens cannot focus light on the retina and everything is blurry. Glasses make the light focus in the right place to make things clear. Long eyeball It is difficult to see objects that are far away when your eyeball is too long. This is known as short sightedness. Contact lenses are made of very thin plastic. get into it Canyouseeanu mber? If not, you m aybecolourblind . Close one eye and hold a finger in front of your nose. Open that eye and close the other one. The finger appears to move! Each eye sees things differently.
40. 40. Your brain works out what you’re seeing by comparing the images it gets from your eyes to things you have seen in the past. Sometimes it can be fooled! Yourbr ain combines images from bo th eyes. Your blind spot is the part of the eye that can’t see anything. It is where the optic nerve leaves the back of your eye. Brain and senses Eye to brain What can you see? The dark blue in these pictures shows how much animals can see clearly. Light blue shows what they can see less well. Humans have to move their heads to see clearly to the sides or look back. Tigers see well to the front to help them find and catch their prey. Zebras keep a look out for movements to the sides so they can avoid attack. To the brain Our eyes swivel around constantly, taking in sights and adjusting to focus on different things. The information they collect travels to the brain through the optic nerve at the back of the eyes. The yellow areas are the parts of your brain that deal with information from your eyes. Ducks can see all the way behind them, even while facing forwards. Chameleons see small areas clearly. They swivel their eyes to see all around. Eyeball Optic nerve 42 What is it called when you look at something and think it’s something else?
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