Human Body Encyclopedia

HumanBody Encyclopedia A DORLING KINDERSLEY BOOK

LONDON, NEW YORK, MUNICH, Contents MELBOURNE, and DELHI Human body Senior editor Penny Smith Senior art editor Cheryl Telfer 4-5 Your amazing body 6-7 What makes you you? Editors Ben Morgan, Zahavit Shalev 8-9 Building blocks Additional design Jacqueline Gooden, 10-11 Organizing the body Tory Gordon-Harris, Claire Patane, Laura Roberts Skeleton and bones Illustrator Peter Bull Digital illustrator Pilar Morales 12-13 Skeleton 14-15 Head case Consultants Dr Penny Preston, Dr Frances Williams 16-17 Bendy backbone 18-19 Living bone Publishing manager Sue Leonard 20-21 Bone and cartilage Managing art editor Clare Shedden 22-23 Moving joints Jacket design Victoria Harvey Moving muscles Picture researchers Marie Ortu, Rob Nunn 24-25 The body’s muscles Production controller Shivani Pandey 26-27 How muscles work DTP designer Almudena Díaz 28-29 Muscle power First published in Great Britain in 2005 by Brain and senses Dorling Kindersley Limited 30-31 Headquarters 80 Strand, London WC2R 0RL 32-33 Network of nerves 34-35 Touchy feely A Penguin Company 36-37 Taste and smell 38-39 Look out! 2 4 6 8 10 9 7 5 3 1 40-41 How we see 42-43 Eye to brain Copyright © 2005 Dorling Kindersley Limited, London 44-45 Listen here 46-47 Balancing act 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 2 Test yourself with the questions at the bottom of each page...

Heart and blood Reproduction and growth 48-49 Blood flow 94-95 Making a baby 50-51 Boom boom 96-97 Growing in the womb 52-53 All about blood 98-99 Double trouble 54-55 Blood cells Life cycle 56-57 Bumps and cuts 58-59 Hormones 100-101 The early years 102-103 Growing up Lungs and breathing 104-105 Growing older 60-61 Air bags Keeping healthy 62-63 Air and oxygen 64-65 Making sounds 106-107 What’s in food? 66-67 Ah-choo! 108-109 Sleep 110-111 Doctors and dentists Skin, nails, and hair Communication 68-69 All wrapped up 70-71 At your fingertips 112-113 Body language 72-73 Fairly hairy 114-115 Use your hands 116-117 Express yourself Fighting disease Reference section 74-75 Germs 76-77 Body defences 118-119 Amazing facts about YOU! 78-79 Fighting germs 120-121 Through the ages 80-81 Allergies 122-123 Glossary 124-127 Index Digestive system 128 Acknowledgements 82-83 Digestive system 84-85 Chew it over Coloured discs contain facts about special topics, 86-87 From mouth to stomach Circles show such as taste. 88-89 Inside the intestines close-up images Brain and senses Taste and smell you might not Taste and smell Runny nose Urinary system otherwise be able Different tastes When you have a cold, tiny Your nose to see. We need to eat and drink to There are five types of tastes hairs in your nose get clogged and mouth survive, but taste and smell – bitter, sour, salty, sweet, with mucus. This stops them a re linked at are what make these everyday and umami. wafting smell particles deep into the throat. activities so enjoyable. your nose and makes it difficult Bitter foods, such as to smell – and taste – things. Taste detector coffee can be bad for you. 90-91 Waterworks Your tongue is a big muscle covered Most poisons are bitter. Sensitive nose in clusters of taste buds. Each cluster 92-93 The stretchy bladder recognizes a particular kind of taste. Sour foods include lemon Much of what we and vinegar. Food that think of as taste is has “gone off” tastes sour. actually smell. Salt detecting taste buds The back of your can be found on the lips as well as on the tongue. nose is linked to your mouth so “Get into it” activity Sweet foods naturally you can smell attract us. Our first food your food as – milk – is sweet. you chew it. buttons show you how Bitter Umami is the savoury ome noses can recogniz Sour Sour taste of foods like soy you can try things Salt sauce and mushrooms. buds are crammed out for yourself. 10,000 taste e 10,000 different sme ngue. Sweet Salt S get into it Taste buds lls. Saliva in your Try putting mouth dissolves onto your to Smell receptors sugar on different places your food. The food Special cells deep inside your nose on your tongue. It tastes washes over tiny taste sweeter in some places buds between the bumps recognize scent particles floating in the air. These cells link than others. Now try on your tongue. Taste buds directly to your brain. salt, lemon juice, recognize different flavours. and coffee. 37 36 1000-1500 millilitres. How much saliva does an average person produce in a day? 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. 3 You will always find the answers here!

Human body Become an expert... Your amazing body on the skeleton, The greatest machine you’ll ever own is pages 12-13 your body. It’s more complicated than any computer, it on digestion, lasts for a lifetime, and pages 82-83 it’s yours for free. Body parts Hair Your body is made up Forehead of hundreds of different parts. You probably know Ears Inside your body the names of the bits you Cheeks Eyebrows Doctors can see can see, but there are many more hidden inside your body deep inside you. with special cameras. Nose Eyes X-ray cameras take pictures of hard body Lips parts like bones. Other Teeth cameras, called scanners, can see soft body parts. ands Fingers Two of everything H Body parts often come Wrists 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. A chest X-ray shows the bones in your chest. The white shape in the middle is the heart. 4 What do we call the study of the human body?

Water, water Your amazing body Water is the most important chemical Curiosity quiz in your body. About two-thirds of your Take a look at the first few pages in this book weight is water. and see if you can find these pictures. The ingredients Your body is made of just a few simple chemicals, plus water. Carbon is the chemical in diamonds and coal. A fifth of you is carbon. Iron makes your blood red. You have enough to make one small iron nail. Robot Phosphorus is in the tips of matches, as well No substitute as your bones and teeth. The human body is too complicated for robots to Sodium and chlorine copy. Robots can copy the make salt. Blood is one- way we walk, but they third as salty as sea water. can’t think or feel like we do. Potassium is used in some types of soap. It’s also in your body fluids. Nitrogen is important in muscles. It’s also the main ingredient in air. Chimps have Compared to chimps, Being human hands like ours. our bodies look almost Although we look different to hairless. animals, our bodies are similar Chimpanzee on the inside. Our closest animal relatives are chimpanzees. 5 Anatomy.

Human body What makes you you? 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. Fair skin Green eyes Curly hair Black hair Unique The shape of your face, the colour of your hair, and many other things Freckles make you unique – different from everyone else. 6 How many genes are there in the human body?

What makes you you? 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. There’s e This girl has a gene that allows get into it her to roll up her tongue. The DNA boy doesn’t have the gene, Look in a Your genes so he can’t roll his tongue. mirror and see if you are stored in can roll your tongue. Don’t a chemical called DNA inside you to cheat by squeezing it with DNA, which looks like a un a twisted ladder with four stretc your lips. Test your different types of rung. The rungs make up a nough family to see who four-letter alphabet that spells out your genes, h to the S has the gene. like letters in a book. DNA can nd back 400 times. split and copy itself. In the family Learning to ride Your genes came from your parents. a bike changes your Half come from your mother and brain and your half come from your father. If you look like your parents, it’s body. because you share the same genes. Changing body Genes don’t control everything – experience also shapes you. If you exercise a lot, for instance, your body gets stronger. 7 About 30,000.

Human body Building blocks 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. The nucleus DNA is controls the rest stored in of the cell. the cell nucleus. The inside of NA a cell is packed D The skin on your with a kind of fingertips is made living jelly called of lots of small cytoplasm. ridges. 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. Before a cell divides, the nucleus splits to make two nuclei. The outer skin, or Tiny generators membrane, stops provide cells with things leaking out. power. Making new cells The new cells pull apart A cell makes new cells by dividing. and separate, but they The two new cells are half the size, but they soon grow back. Millions of usually stay close your cells die every second, but millions neighbours. of others divide to replace them. 8 How many cells are there in the human body?

How big are cells? Building blocks Cells are too small to see with the More than 2000 dead skin cells f naked eye, but scientists can ell off you while you read this sentence. photograph them through powerful microscopes. The cells on your skin are about a hundredth of a millimetre wide. A microscope can The cells on zoom in to see the the surface of tiny, flaky cells on the your skin are tough ridges of and flat. They overlap to a person’s fingerprint. form layer of armour that protects the softer cells below. Fat cells are Many blood cells Nerve cells are thin Bone cells make Cells make tissue bubble shaped. are red. They carry and wiry. They your bones hard. Your body contains They store fat oxygen around the carry electrical They live in tiny hundreds of different under your skin. signals. holes in bones. types of cells that do body. different jobs. Cells of the same type usually About 100 trillion. group together to form tissue. Fat, muscle, bone, and nerves are types of tissue. Blood is a liquid tissue. 9

Human body Systems Organizing Organs and the body tissues work in teams to carry out Your cells and tissues are major tasks, like organized into larger body transporting blood parts called organs. In turn, or processing food. your organs work together These teams are to form body systems. called systems. Kidney The heart is the largest organ in Heart the blood system. It pumps blood around Brain the body. Organs The tubes that carry blood away from the An organ is a body part that heart are called does a specific job. Your heart’s arteries (shown in job, for instance is to pump red). blood. Kidneys clean blood. The tubes that carry blood back to the heart are called veins (shown in blue). Organ transplant Heart and blood If a vital organ stops working, doctors Your heart, blood, and may replace it with an organ from another blood vessels make up the blood system. It person. This is called a transplant. transports vital supplies around your body. 10 Which body system makes your stomach rumble?

Muscles Muscles change Organizing the body Your muscle system is made the position of your Other systems of tissues that move parts skeleton by pulling of your body by pulling different bones. Some of your other on them or squeezing important systems them. Your biggest are shown in this list. muscles all pull on bones. Breathing system: the main organs are your Your fingers lungs, which take in air. are moved by muscles in Hormone system: this your arm. uses powerful chemicals to control your body and mood. The most powerful muscles are Skin, hair, and nails: in your legs. these form your body’s protective covering. Skeleton Immune system: this Bones and seeks and destroys germs that get into your body. joints make Urinary system: this up the skeletal cleans blood and gets rid of waste chemicals. system, an Reproductive system: inner frame these are the organs that make babies. that supports Digestive system the body. A quarter of Your digestive your bones are organs break Nerves in your feet. down food to provide your Your nervous system carries body with energy and raw materials. electrical signals around Your mouth is the first your body. You need part of the digestive Signals shoot this system to see, system. along nerves to muscles, hear, think, A long, twisting tube telling them makes up your when to pull. and react. intestines, where digested food is Senses, such as Your brain is the touch, rely on nervous system’s absorbed. nerve cells that control centre. send signals to 11 your brain. The digestive system.

12 How many ribs have you got? Skeleton Skull Smallest bone Skeleton and bones Jaw bone Around the same length Your bones all join up to as a grain of rice, this make a frame for your body is one of the smallest called the skeleton. This bones in your body. It protects your insides, and helps you move about. lies deep inside your ear. Shoulder A giraffe’s long blade neck helps it to eat leaves Each finger off tall trees. has three bones, except for your thumb, which has two. You have eight small bones in each wrist. 206 bones There are Rib Neck bones 24 bones in Pelvis Did you know that you There are 206 bones your spine. have seven bones in your in an adult skeleton. neck, the same number Over half of these are found in as a giraffe? The top one the hands and feet – the parts allows you to move your of your body that perform the head up and down, the most complicated movements. second lets you rotate it from side to side. 24, unless you are one of the rare people born with 26. The thigh bone is the biggest and strongest in the body. Your tail bone is Frogs have very short at the very spines to withstand the 13 bottom of your strain of the huge leaps spine. they take. Long lasting Thigh bone Snakes are A fish’s Bone is a very hard incredibly bendy spine allows it material and one of the last Shin bone thanks to many to bend its body from parts to rot away when a identical side to side so it can body is buried. This woman Your ankle has vertebrae forming swim smoothly. lived in the Stone Age, 5000 three larger their long spines. years ago, but her bones bones and four have survived until today. smaller ones. Other skeletons Skeleton Become There are 54 Most animals have a an expert... bones in your backbone and are called hands, and 52 “vertebrates”. Animals on bone and cartilage, in your feet. with no spine, like spiders pages 20-21 on teeth, and bugs, are called pages 84-85 “invertebrates”.

Skeleton and bones Head case The frontal bone forms your forehead. The most complex part of the is the domed part of your skeleton is the skull. It is cranium made of many bones Helmet that fit together sk tightly, to protect The upper part of the skull the brain and The is like a helmet that protects ull. support the face. the brain. The lower part forms a structure for your Eye sockets are facial features to attach to. made up of seven different bones. The brain fills The front of the most of the nose has no cranium. bones. Label Facial features Teeth are set This image shows the relationship into the between your skull and face. There upper and are no bones shaping the front part lower jaws. of your nose, your lips, or your ears. Your nose and ears are 14 shaped by cartilage. Why does a baby have spaces between its cranial bones?

The spinal cord Head case goes through a large hole in the k of the Bac head skull. Blood vessels pass through small holes in the skull. There are two Upper jaw The lower parts to the jaw is not upper jaw. shown here. The lower jaw is Jigsaw Hole in the head hinged. It is the only The skull From underneath you can skull bone that can bones fit clearly see the big hole at the move. together like the bottom of this skull. The spinal pieces of a jigsaw. cord – which runs down your back – meets your brain here. All but one of the bones are locked in place. This makes the skull very strong. Meet the relatives Face from the past Chimpanzees and humans share a common ancestor. Scientists can work out what a However, chimps have smaller brains than humans so dead person’s face looked like their craniums are smaller. Chimps also have a large from their skull alone. They ridge above their eyes, and a jutting jaw. examine the facial bones and build up artificial cartilage, muscle, and skin over them. 15 So its head could withstand being squashed while it was being born.

Skeleton and bones Bendy backbone 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. ont of spinThe first sevenStack of bonesThe thoracic Back of spinebones are in your vertebrae form neck. They are Your spine contains 24 Your spine curves gently, a bit like the letter “s”.known as theseparate bones calledjoints with cervical vertebrae. vertebrae. At the bottom the ribs. are nine more vertebrae. The next 12 They are much smaller A straight are called the and are fused together. back is thoracic actually quite vertebrae. curvy. The five lumbar Fr The fused vertebrae bear bones of the most of your sacrum and weight. coccyx don’t allow much movement. The five sacral e vertebrae are fused together. The spinal cord goes through this hole. Segments of the spine The coccyx Each vertebra has a strong, stubby consists of four section that supports the weight of fused vertebrae. your body, and a hole for the spinal cord to pass through. 16 What is a slipped disc?

Shock absorbers Bendy backbone You twist and bend your spine almost every time you move. Ribcage Sandwiched between the vertebrae Your thoracic vertebrae are pads of cartilage to stop them connect to your ribs. banging and rubbing against each Together they form a other and getting worn out. cage around your heart and lungs. Rib bones Space for Pad of are curved. They are spinal cord cartilage also thinner and more bendy than the bones in your spine. The pads give A woman’s pelvis is shaped you a little bit differently to a man’s. A baby can Vertebra of movement pass through it in all when she gives birth. could be this directions. Pelvis Yo u bendy...... Reproductive organs and some digestive organs rest in the The way the bowl-shaped hollow of your back curves pelvis. The sacral vertebrae means we can’t bend as far and coccyx form back as we can the bottom forwards. of the bowl. Bendy backbone geBtenidnotvoer. i ...with a lot of practice! The amount of Gently feel the t movement between bones of your spine each vertebra and its with your fingertips. neighbours is actually Can you follow very small, but added them from neck together they allow for a large range of to waist? movement. 17 It’s when one of the pads between the vertebrae gets damaged.

Skeleton and bones Marrow can be found in the spine, skull, Living bone and the main leg and arm 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. 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. Spongy bone Bone marrow Parts of some bones have a A jellyish substance honeycomb structure with lots of called marrow fills spaces. This makes them weigh less the centre of many of than if they were solid right through. your larger bones. It supplies your body Compact bone with red blood cells The hardest and most at a rate of 3 million dense part of the bones is cells per second. the outer layer. It is made of calcium, a substance we get from our food. Teeth are made of calcium too. 18 What are the most commonly broken bones?

Broken bone Living bone Bones are strong and flexible enough to cope Curiosity quiz with a lot of pressure, Take a look through but, as this X-ray the skeleton and bones shows, they sometimes pages and see if you break. Luckily they can identify where these can heal themselves. bony bits come from. If the broken bone Become ends have slipped an expert... apart they must be repositioned on the skeleton, by a doctor before pages 12-13 healing begins. on skin and nails, On the mend pages 70-71 New cells form at each end of the broken bone, closing the gap between them. It takes about 6 weeks for this to happen. iloyneosura lreatsetitlleens. Padded clothes gYroowurinbg unt help protect bones from sudden impact. 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. Fingers, wrists, and arms. 19

Skeleton and bones Baby’s hand Bone and cartilage 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. Making bones More, less Babies’ bones are made out You’ve got more bones of a soft and bendy material than your mum or dad! called cartilage. Slowly this hardens and turns into bone. You were born with over 300 “soft” bones, but as you get older, many fuse Baby bones are entirely made of soft, growing together. By the time you’re 25 you’ll cartilage. have 206 fully formed bones. Adolescent bones are Cross-section of an mostly bone, with a small ear – the cartilage sits amount of cartilage. between two layers of skin. Adult bones have stopped growing. Most no longer contain cartilage. Stick out your ears! Your ears are made of cartilage, not bone. They are strong, but much more bendy than your bony bits. 20 Which foods are rich in calcium, the mineral you need to grow healthy bones?

Child’s Bone and cartilage hand Adult’s hand Bone shows up as purple in these X-rays. The difference between the amount of bone can clearly be seen. 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 Smooth coated joints the ends of these The ends of neighbouring bones are covered in bones. smooth cartilage. That way, they can glide against The pads of each other when you move. cartilage get squashed from standing up and stretch back out while you’re lying down. Milk, cheese, yogurt and ice-cream. 21

Skeleton and bones Moving joints Joints are the places where bones meet. Different kinds of joints allow you to move in different ways. Hinge joint Fixed joints The bones that make up Your knee can bend your skull start to join up in the middle but soon after you are born. it can’t swing from Once they have fused, side to side. This none of them allow joint has a hinge movement except the like the one that hinged jaw joint. allows you to open and Knee joint close a door. Have you ever used a joystick? That’s a ball and socket joint! Ball and socket Your hips are ball and socket joints. They allow you to move your legs in There are 19 moveable joints in all directions and even to turn them. your hand – not counting the ones in your wrist! 22 What is tennis elbow?

Moving joints Bendy bits Your hand is a terrif ic feat of engineering! Different sorts of joints get into it all over your body keep you moving. Tape your Thank your thumbs thumb to your first Your thumb is the most Neck bones feature a flexible of your fingers. pivot joint that allows finger. See how You rely on your thumbs your head to turn. difficult it is to open a whenever you handle notebook, pick up a delicate objects. Wrists have a joint that allows them to turn but pen, and write This woman has not to go right round. your name. stretchy muscles and ligaments that Ankles contain different Hip hooray allow her spine joints for up and down Joints, particularly to bend and side to side movement. knee and hip joints, further than sometimes wear out in most people old age. When this can manage. happens, doctors can remove the worn-out joint and replace it with an artificial one. Ligaments Fabulously flexible Bands of tissue called ligaments act People whose like elastic. They hold your joints are bones together yet particularly still allow you flexible are to move. called “double- jointed”. The condition Ligament can run in families, but people who are double- Your elbows Bone jointed must practise if have a hinge they want to keep their joint for bending ligaments stretchy. and a pivot joint so they can turn. The name for sore elbow tendons caused by overuse. 23

Moving muscles The body’s muscles Every time you move, you use Pulling strings muscles. Muscles make you walk, blink, and smile. Some muscles About 650 of your muscles are work without you thinking about them, but others need to be told to wrapped around the bones of move. They all work by shrinking, your skeleton. They move your which makes them pull or squeeze. body by pulling on the bones. Together they form the muscle Smooth muscle The pectoralis system. This type of muscle muscle swings makes things move your arm. inside your body. It mixes food in your The biceps muscle stomach and pushes bends your arm. Smooth muscle cells food through are short your intestines. with pointed ends. Heart muscle cells Heart muscle Your longest muscle are stripy with When you put your is the sartorius. It oval blobs. hand on your chest, helps cross your you can feel your legs. Skeletal muscle cells are heart beating. Your long and heart is a strong The tibialis muscle threadlike. muscle that squeezes bends your foot. blood around your body. 24 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. What weighs more: all your bones or all your muscles?

The body’s muscles Muscle magic Who’s in charge? Muscles have hundreds You use hundreds of muscles when of uses. They make up about a third of your you run and jump. Your brain body weight. controls them all, a bit like Become Largest muscle: you use a conductor controlling an an expert ... the muscle in your buttock orchestra. It sends signals for sitting and walking. along nerves to every on making sounds, pages 64-65 Fastest muscle: this one makes you blink. It works muscle, saying on how intestines up to 5 times a second. exactly when push food, to work and Ear wiggling: a few pages 88-89 people can control the muscles around their ears. when to rest. Smile: a fake smile uses Hundreds of muscles different muscles from a work in a carefully real, involuntary smile. controlled sequence when you jump in the air. 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. at le. at leYmaosuatrk1te4oindtgiafufmeeraceoznintntmgaliuynssfclleexsitbh Your muscles. 25

Moving muscles How muscles work Muscles work by contracting, which means they shorten. As a muscle contracts, it pulls. The larger the muscle, the more powerfully it pulls. When the bicep Working in pairs muscle contracts, it pulls your forearm Muscles can pull but and bends your not push. They work arm. in pairs that pull in opposite directions. When one muscle pulls, its partner relaxes. When the triceps Your forearm muscle contracts, it contains pairs straightens your of muscles that arm. move your hand and fingers back and forth. 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. A typical muscle Bundle of One muscle cell Myofibrils inside muscle cells a muscle cell 26 Where is the body’s smallest muscle?

Try raising your Tendons How muscles work ring finger with Muscles are fastened your hand in this to bones by tough bands Making faces position. called tendons. When you It’s stuck because wiggle your fingers, you Muscles in your face are it’s joined to the attached to skin as well same tendon can see the tendons as bone. They pull the as the middle move on the back skin when you change finger. of your hand. your expression. You use about 17 muscles when you smile. Middle finger Ring finger 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. 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. Getting a stitch 27 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. In the ear.

Moving muscles Stamina If you have stamina, you Muscle power can keep going for a long time without getting tired. The more you use your muscles,the Exercise that makes you feel better they get. Active games and out of breath, like running, exercise make your muscles larger, improves your stamina. 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. This contortionist has made her body Strength more flexible by doing exercises that Pushing, pulling, and lifting make stretch her back. your muscles bigger and stronger. Bodybuilders lift heavy weights over and over again until their muscles are enormous. You need strong muscles to win a tug-of-war. Become an expert ... on how your heart works, pages 50-51 on healthy food, pages 106-107 28 What happens to muscles if you don’t exercise?

Muscle food Muscle power Ways to keep fit To build strong muscles, you need a type of food Exercise is very good for called protein. Meat, your health. As well as fish, beans, milk, and making your muscles eggs are rich in protein. bigger, it strengthens your heart and lungs. Most vegetables don’t contain much Walking to school, or protein. going out for walks, builds strength and stamina. Body heat Chicken Milk This picture shows the Fish Egg Football is great for heat of a man’s body. improving your flexibility Muscles make heat when Beans and strength. they work hard, which is why exercise makes you Fish is a very Swimming strengthens hot. On cold good source of your heart muscle and days, your protein. builds stamina. muscles try to warm Cycling strengthens your you up by leg muscles and builds shivering. up stamina. Dancing keeps your body supple and helps build strength. They get small and weak. 29

Brain and senses Sense signals The cerebrum is Headquarters the main part of your brain. The brain is the body’s control It gets and stores centre. It is a complicated organ sense information that works very quickly, a bit like a brilliant, and also controls living computer. your movements. Cerebrum Clever calculator Cerebellum ain stem The cerebrum is also responsible for Br thinking, speaking, and complicated Your brain stem tasks such as sums. works at the same rate whether you’re awake or asleep. Muscle control 24 hours a day Your cerebellum helps you Whatever else you do, to balance and move your the brain stem makes muscles. You use this bit of your brain when you dance. sure your heart and breathing never stop. 30 Does your brain hurt when you have a headache?

Headquarters Skull In relation to the size Curiosity quiz of our bodies, humans have Brain the biggest brains of any Take a look through the brain and senses pages animal. and see if you can spot Brain box Your skull is a bony shell where these come from. that fits together like a jigsaw around your brain. Shock- absorbing liquid fills the space between the brain and skull. 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. 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. 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. No, your brain can’t feel pain but the muscles around your head can. 31

32 Which is the longest nerve in your body? Network of nerves Brain and senses All of the body contains nerve cells. These link up to form the network of nerves we call the nervous system. It Brain transports messages between A good night’s sleep Your body and brain slow down when the body and the brain. you sleep, but they don’t stop working. Your brain needs sleep to sort out the Quick as a flash events of the previous day. Nerve cells lie next to one Cross your Your knee jumps legs and tap forwards even another forming long chains. just below the though your brain knee. hasn’t They pass messages to their told it to move. neighbours – rather like a Spinal cord – speedy relay race – to and the centre of the network from the brain. Brain cells viewed through a microscope. 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. The one running from your big toe to the base of your spine. Messages You’ve got 150,000 km Pain-killers (93,200 miles) of nerves When you get a filling, Messages travel faster than a high-speed train.Your brain in your body. the dentist gives you an controls your body. anaesthetic. This drug It receives messages from all parts of stops nerves passing your body and on pain messages for decides what to do. a short time. 33 Walking is the result of Pins and needles Network of nerves your brain telling your Sitting cross-legged for a long time leg muscles to move. squashes the nerves in your legs. When you stand up, the nerves start to work Hunger is your stomach again, producing a tingling feeling. telling your brain that it’s empty and you must eat. 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. Pain gets a very quick response. You move away from what’s hurting you. Blinking happens without you needing to think about it. Breathing is automatic too. It carries on even when you are asleep.

Brain and senses Merkel’s disk responds to light touch and Touchy feely is sensitive to the texture of Your skin is in immediate contact with things. 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. Things we can feel Not worth noticing Meissner’s Although your brain receives messages all corpuscle senses Skin is packed with many sense receptors. the time, it filters out the less important light touch. Each sort responds to ones. That’s why you’re not constantly different sensations. aware of the clothes against your skin. Warmth is detected by It feels slimy!.... nerve endings quite close to the surface of the skin. Cold is felt by different sensors to heat. Extreme cold registers as pain. Deep touch sensors This girl quickly Ouch! enable you to grip moves her finger things tightly. The body has away from the its own system of Light touch sensors lie thorn to stop alarm bells. Pain at the root of hairs on the pain. receptors warn us your arms and legs. when a part of the body has been Vibrations from an hurt or is about electric drill trigger vibration sensors. to be harmed. Tickly feelings result from a light and unexpected touch. Sensitive fingertips full of receptors are able to tell coins apart. 34 How many touch receptors are in a fingertip?

Touchy feely Free nerve endings respond to heat, cold, and pain. Surface of skin The Ruffini ending Dermis responds to firm or Fat continuous touch. Under the skin Dead cells form the surface of your skin. Below that lie sweat glands, hair follicles, and different types of sensory receptors. The Pacinian corpuscle responds to firm pressure and vibration. message shoots off to the brain.... .... the Sensitive bits Reading by touch Braille was Braille is a system that invented over 150 Skin contains more touch uses raised dots to represent receptors than any other letters and numbers. It was years ago. part of the body. But invented so that people with some areas are more bad eyesight would be able B I RD sensitive than others. to read by feeling the page with their fingertips instead get into it Fingertips are packed of looking at words. with sensors, especially Put one finger light pressure receptors. in cold water, one in hot, then put both in warm water. Lips have very thin skin The water feels cold to the which is good at detecting hot-water finger and hot heat and cold. to the cold-water finger. Toes are very sensitive, 35 but thick skin makes the heel less sensitive. About 3,000. That’s roughly the same as on the whole of the trunk of your body.

Brain and senses Different tastes Taste and smell There are five types of tastes – bitter, sour, salty, sweet, We need to eat and drink to and umami. survive, but taste and smell are what make these everyday Bitter foods, such as activities so enjoyable. coffee can be bad for you. Most poisons are bitter. Taste detector Sour foods include lemon Your tongue is a big muscle covered and vinegar. Food that in clusters of taste buds. Each cluster has “gone off” tastes sour. recognizes a particular kind of taste. Salt detecting taste buds can be found on the lips as well as on the tongue. Bitter Sweet foods naturally Sour attract us. Our first food Salt – milk – is sweet. Umami is the savoury Sour taste of foods like soy sauce and mushrooms. buds are crammed 10,000 taste Sweet Salt ngue. get into it Taste buds onto your to Saliva in your Try putting mouth dissolves sugar on different places your food. The food on your tongue. It tastes washes over tiny taste sweeter in some places buds between the bumps than others. Now try on your tongue. Taste buds salt, lemon juice, recognize different flavours. and coffee. 36 How much saliva does an average person produce in a day?

Taste and smell Runny nose Your nose and When you have a cold, tiny mouth are hairs in your nose get clogged with mucus. This stops them linked at the wafting smell particles deep into throat. your nose and makes it difficult to smell – and taste – things. 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. ome noses can recogniz S e 10,000 different sme lls. 1000-1500 millilitres (35-53 fl oz). Smell receptors Special cells deep inside your nose recognize scent particles floating in the air. These cells link directly to your brain. 37

Brain and senses Wandering eyes Look out! Six muscles control each eye. You use both eyes when you Sight is the body’s main sense and look at something, so your the main way we learn about our eyes move together. surroundings. Two-thirds of the information we take in comes Sclera (or white from our eyes. of the eye) Iris Pupil The muscles The middle of the surrounding your eyeball is filled eyeball make precise with fluid. movements so you can smoothly track moving iqureint objects. At n 1.6 km (1 mile) away. ight, our eyes could d Aansiraisfiinsgaesrpun Pupil Eyelid Sc lera Hidden away Iris Most of your eye nestles etect a lighted candle 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. 38 What is the sleep that collects in our eyes?

Tears are made behind Safekeeping Look out! each eyelid. Your eyes are fragile, Eye colour The iris is the coloured squidgy balls made of part of the eye. All eye colours are produced by watery jelly so they need one substance, melanin. Lots of melanin results Tears drain into tear ducts. to be well protected. in brown eyes, less These link to your nose, means a lighter shade. which is why your nose runs Bone in your skull when you cry. surrounds your brain and the backs of the eyes. Crying Tear glands behind your eyes Eyebrows sit above your produce drops of salty fluid. eyes and prevent sweat When you blink, your eyelids dripping into them. sweep this fluid over your eyes to keep them clean. If something Eyelids and lashes stop gets into your eye, or you feel dust entering the eyes and strong emotions, the drops turn then sweep it well away. into floods of tears. Your pupils change size automatically. Either it’s dark or this 39 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. Dust and mucus washed from our eyes as we sleep.

Brain and sensesLight re How we see 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. flects off an object and enters your eye. The eye is filled with a semi-solid jelly. Optic The lens is clear and An object nerve flexible. It focuses on The pupil is a hole The retina things by changing that lets light into contains cells shape. the eye. that sense light. How your eye works Light from an object enters your eye Seeing in colour through the pupil. It passes through Your eyes contain millions the lens, and makes an upside down of cells. Cone cells give you image on the retina at the back of your eye. Cells in your eye send colour vision but don’t messages down the optic nerve work well in dim light. to your brain. Your brain Rod cells work well flips the image back the in dim light but see everything right way round. in shades of grey. 40 What is an eye specialist who tests eyesight called?

Blurry vision Can you see a nu How we see Sometimes an eyeball is the wrong shape. mber? If not, you m The lens cannot focus light on the retina and ay be colour blind everything is blurry. Glasses make the light focus in the right place to make things clear. Short eyeball If you have a short eyeball you will have difficulty seeing things close up. This is called long sightedness. An optician. Long eyeball Colour blindness It is difficult to see . objects that are far away Some people cannot tell certain when your eyeball is too colours apart, especially red long. This is known as and green. This is called colour short sightedness. blindness. It is more common in men than women. get into it Glasses bend the light entering Close one eye Contact lenses and hold a finger in front These work like your eye so it of your nose. Open that eye mini glasses and focuses on the and close the other one. sit directly in front of the retina. The finger appears to eye. They’re a move! Each eye sees bit fiddly, but things differently. once they’re in you can’t feel them at all. Contact lenses are made of very thin plastic. 41

Brain and senses What can you see? Eye to brain The dark blue in these pictures shows how much Your brain works out what you’re animals can see clearly. seeing by comparing the images it gets Light blue shows what from your eyes to things you have seen they can see less well. in the past. Sometimes it can be fooled! Humans have to move ain combines images from bo their heads to see clearly Your br th eyes. 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. 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. The yellow areas are the parts of your brain that deal with information from your eyes. Optic nerve 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. Eyeball 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. 42 What is it called when you look at something and think it’s something else?

Tallest tower Eye to brain Does the green tower look taller than the Finding your blind spot others? That’s because Close your right eye and look it’s further along the directly at the star. Slowly track and we expect bring the book to your left eye. objects further away You reach your blind spot from us to look smaller. when the circle disappears. The colours of the towers also affect the size they seem to be. In fact, all the towers are exactly the same size. Recognizing objects Your brain is very clever – it can recognize this car from different points of view. A computer would have to be taught that both these pictures are of the same object. Certain patterns trick your eyes into seeing movement where there is none. Do you believe your eyes? Your brain helps your eyes to understand what they see. Sometimes you see things that aren’t actually there... You see a heart even though the edge of the shape isn’t there because your brain uses the information it has to fill in the gaps. An optical illusion. 43

Brain and senses How well can you hear? Listen here Your hearing range is from When you shout you send out the highest to the lowest invisible sound waves through notes that you can hear. the air. Your ears pick up the waves and transmit Adults have quite a the sound to your brain. small range compared to other animals. The speed of sound Children hear higher We don’t notice the slight notes than adults. Your delay between someone’s range shrinks with age. lips moving and Cats, dogs, and rabbits the sound actually can hear much higher reaching our ears. notes than people. It’s too fast! Bats have excellent hearing. Their range is five times as large as ours. Sound travels through the Headphones feed different sounds into each ear so you feel as if you’re surrounded by instruments. Why two ears? Sounds normally reach one ear first and then the other. This helps our brains work out where sounds are coming from and how far away they are. 44 Why do we have ear wax?

Outer ear Listen here What we call the ear is A little help really just the part that Partially deaf we can see. Sounds are people may use hearing aids. collected here, and These make the funnelled inwards. sounds entering the ear louder and easier to hear. Middle ear Sounds arriving here from the outer ear cause the eardrum to vibrate and set off movements in three tiny little bones. MiBonesCochlea Outer Ear canal ear ddle ear r ear air to your ear. Ear drum Inne Inner ear Tiny hairs are moved by sounds. The bones moving cause vibrations in the liquid Signals travel deep inside the ear. along these nerves Tiny hairs in your to the brain. inner ear pick up these vibrations in the liquid around them. The hairs are attached to nerves, which connect to your brain. To protect the skin lining the ear canal, trap dust, and repel insects. 45

Brain and senses Balancing act As well as hearing, ears help you balance. Sensors in your ears work with The three those in your eyes, semi-circular muscles, joints, and feet canals deal with balance. to let your brain know Ear hole your body’s position. Keeping track Deep inside your ear are three tiny tubes filled with fluid. They detect the movements your body is making and let your brain know about them. One tube is for forward and Watch your step! backward movements, another for up and down, and the Keeping your balance third for side to side while walking along movements. a narrow wall takes a lot of concentration. A jelly-like knob floats in You are responding each tube. Inside it are to information coming from your eyes, sensitive hairs that detect muscles, and ears movement. at the same time. 46 The movements travel along the hairs, through a nerve, to the brain. Can astronauts learn to balance in space?

Balancing act The more you practise the better you will be at balancing. Basically, your Motion sickness Travelling in a car, boat, or plane can make you feel ill. Your eyes tell your brain that you’re staying still in the vehicle, but your body says it can feel movement. This confusion is what causes motion sickness. brain is the boss. Muscle messages When you move, sensors in your muscles send messages to your brain. If a movement isn’t going right, your brain will make you do things differently. The brain get into it First make sure there is nothing unsafe nearby for you to crash into. Then spin round and round and make yourself feel dizzy. Why do you feel dizzy? 47 The liquid in the tubes of your ear is like water in a cup. When you spin, it continues to slosh around for a while even after you’ve stopped. Your brain gets confused about which way round you are, and you feel dizzy as a result. Yes, but it can take a couple of days to learn how.

48 When you cut yourself, what kind of blood vessel does the blood usually come from? Blood flow Tube transport Heart and blood Blood is the body’s Blood leaves the heart in transport system. large blood vessels called Pumped by the heart, arteries, and it returns it travels around the in vessels called veins. body in tubes called Between the arteries blood vessels, delivering and veins are tiny vital supplies to keep vessels called your cells alive. capillaries. Blood picks up Lung Lung Artery oxygen from the lungs and carries it Each major organ around the rest of has an artery the body. bringing fresh blood and a vein carrying Around the body away used blood. Blood travels round Liver The aorta is the biggest Vein your body, passing Stomach blood vessel in your through organs on body. It is as thick as the way. It picks your thumb. A blue up oxygen in the whale’s aorta is wide lungs and food in enough to swim through! the liver, then gets rid of waste Kidney Kidney in the kidneys. The vena cava is your Capillary biggest vein. body. Capillaries km Arteries split into in your smaller and smaller branches. Eventually Become (60,00T0hemrileesa)reofabbloouotd1v0e0s,s0e0ls0 Artery they turn into capillaries, an expert... Vein which are finer than hairs. Capillaries lead into veins, on breathing in which join together and get and out, pages 60-61 bigger on the way back to the heart. on air and oxygen, A capillary. pages 62-63 Capillaries From red to blue Arteries Blood flow Veins The colour of blood 49 depends on how much oxygen it contains. Oxygen-rich blood in arteries is brilliant red. Oxygen-poor blood in veins is dark, purplish red (shown blue on the diagram).

Heart and blood Double pump Boom boom Your heart is really two pumps in one. One half pumps blood through Your heart is a pump that your lungs, and the other half pumps pushes blood around your blood around the rest of your body. whole body. Each time your heart beats, it squirts out a Blood from most of Blood goes out to small cupful of blood and the body enters the body through the refills for the next beat. through the vena aorta. cava. Where is it? Blood goes Your heart is in the middle of out to the your chest, squeezed between lungs. the two lungs. You can feel its beat just left of the bone in One side pumps blood to the lungs... the middle of your chest. Blood comes in from the lungs Vena cava Aorta Blood comes Blood goes out from the body. to the body. 50 How many times does your heart beat in a year?

One-way system Boom boom To keep blood flowing one way only, your Curiosity quiz heart and most veins contain valves. Your heartbeat is the sound of valves shutting Take a look through the when your heart squeezes. heart and blood pages and see if you can spot any of the cells and tissues below. Blood goes out to Valves stop blood the lungs. flowing backwards. he other pumps blood everywhere else.Blood comes in from the lungs. Beating faster Muscles need extra blood when you’re active, so your heart speeds up. It beats about 70 times a minute if you’re resting but up to 200 times a minute if you’re running. ...and t get into it Find your pulse by pressing two fingers on your wrist. You should be able to feel a gentle throb as your heart pumps blood around your body. About 40 million times. 51

Heart and blood All about blood Blood is a warm, soupy mixture of liquid and cells. The cells carry oxygen and fight germs, and the liquid carries nutrients to body cells and takes away waste. Main ingredients Blood contains three types of cells – red blood cells, white blood cells, and platelets. They float in a yellowish liquid called plasma. One drop of Lots of White blood blood contains plasma cells seek 5 million red blood cells, Yellow plasma out and kill half a million platelet cells, makes up more germs. They also eat up the 7,000 white blood cells, than half of dead cells that water, sugar, salt, your blood. hormones, vitamins, they meet. fat, and protein. White blood Red blood cells make blood red. cells and Become platelets. an expert... on fighting germs, pages 78-79 on air and oxygen, pages 62-63 Red blood cells transport oxygen from your lungs to 52 the rest of your body. How long does a red blood cell live for?

All about blood Your blood type There are four main types of blood, called blood groups. Your blood group affects who you can donate blood to. People with blood group People with blood group A A can give blood only to O O can donate blood to people with A or AB. almost anyone. Blood bank One in ten people People with blood group People with blood group who go to hospital need extra blood, so hospitals keep a store AB AB can only give blood B B can give blood only to of blood in a “blood bank”. The to others with AB blood. people with B or AB. blood is divided into separate supplies of cells and plasma. How much blood? White blood cells The average adult has about 10 pints (5.7 litres) of blood, and platelets fight d but a newborn baby has only a cupful. The amount of blood in your body grows with you. By age 10 you have up to 4 pints (2 litres). Platelets are About four months. cells that become sticky to make blood isease. clot and form scabs. By a year old a baby has more than 1 pint (half a litre) of blood.