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Build your own spacecraft!

Build your own spacecraft!

How would you like to be the chief engineer for an important NASA mission? In this activity, you get to design the latest and greatest satellite. Your satellite could help study things happening on Earth, take pictures of planets in our solar system, keep an eye on our sun, or even find planets elsewhere in the universe!

You get to decide how to make your satellite-its all up to you. While you are building your satellite, though, keep in mind that your satellite must have a couple of basic things:

Click on the image to see what a real satellite looks like!

This is the GOES-N satellite. It keeps watch over weather on Earth.
(Click image to return to the previous illustration)

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STRENGTHEN YOUR ARGUMENT

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Making the Case for Health | PBS LearningMedia

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Students develop and present an evidence-based argument about a change they would like to bring about at their school to make it a healthier place for all students. In this interactive lesson designed for both full-class and individual or small-group work, students examine a similar effort, chronicled in BASIC BLACK: Youth Fighting Fat, in which a group of concerned Boston teens seeks to address the problem of obesity in their community.

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Misty-On Eating Smart: Watch It!

Your body depends on a wide range of nutrients-the substances contained in foods that the body uses to grow and be healthy. These include vitamins, minerals, fiber, and three sources of energy: carbohydrates ("carbs"), proteins, and "good" fats. A well-balanced diet, which includes the right types and amounts of food and drinks, gives your body the nutrition and energy it needs.

In this video, meet Misty. She has diabetes. Eating the wrong kinds of food does not cause diabetes (although it can add to the risk of developing the disease). People with diabetes do have to be careful about the food choices they make to help control the condition. Watch the video to see how Misty plans her diet now that she is in college. Everyone can learn from listening to her talk about what goes into her diet -and what stays out. Click on the right to watch the video.

Then, list three things that Misty does to eat a well-balanced diet in college.

Space

Pause/Play video playback

Enter

Pause/Play video playback

m

Mute/Unmute video volume

Up and Down arrows

Increase and decrease volume by 10%

Right and Left arrows

Seek forward or backward by 5 seconds

0-9

Fast seek to x% of the video.

f

Enter or exit fullscreen. (Note: To exit fullscreen in flash press the Esc key.

c

Press c to toggle captions on or off

Misty-On Eating Smart
You must be signed in to save work in this lesson. Log in

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Your body depends on a wide range of nutrients—the substances contained in foods that the body uses to grow and be healthy. These include vitamins, minerals, fiber, and three sources of energy: carbohydrates (“carbs”), proteins, and “good” fats. A well-balanced diet, which includes the right types a…

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[vietsub+ lyrics] Count On Me - Bruno Mars (free drawings)

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The page or lesson that you are looking for does not exist anymore.

This can have many reasons, one of them being that the Adobe Flash player has been discontinued by Adobe. Several courses of e-learning for kids are still developed in flash and don't work anymore, so we are in the process of creating new and exciting lessons in HTML. Please help us make this possible by making a donation
Donate now to help us

In the meantime, check out and enjoy our 550+ courses that cover the entire Math and Science curriculum grades Kindergarten to 6. Next to the more obvious learning goals, these courses also cover topics like personal hygiene, how the body works, and taking care of our environment. You can visit our Math World portal and our Science World portal via the below buttons

If you have any questions, please contact us via our website: www.e-learningforkids.org

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The page or lesson that you are looking for does not exist anymore. This can have many reasons, one of them being that the Adobe Flash player has been discontinued by Adobe. Several courses of e-learning for kids are still developed in flash and don't work anymore, so we are in the process of creating new and exciting lessons in HTML.

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Grace is doing some science experiments. Can you help her?

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National Geographic

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Koalas are marsupials, related to kangaroos.

OFFICIAL NAME: Commonwealth of Australia

FORM OF GOVERNMENT: Federal parliamentary democracy; Commonwealth realm

CAPITAL: Canberra

POPULATION: 23,470,145

OFFICIAL LANGUAGE: English

MONEY: Australian dollar

AREA: 2,969,906 square miles (7,692,024 square kilometers)

MAJOR MOUNTAIN RANGES: Great Dividing Range, Macdonnell Ranges

MAJOR RIVERS: Murray-Darling, Murrumbidgee, Lachlan

Australia is the only country in the world that covers an entire continent. It is one of the largest countries on Earth. Although it is rich in natural resources and has a lot of fertile land, more than one-third of Australia is desert.

Most Australian cities and farms are located in the southwest and southeast, where the climate is more comfortable. There are dense rain forests in the northeast. The famous outback (remote rural areas) contains the country's largest deserts, where there are scorching temperatures, little water, and almost no vegetation.

Running around the eastern and southeastern edge of Australia is the Great Dividing Range. This 2,300-mile (3,700-kilometer) stretch of mountain sends water down into Australia's most important rivers and the Great Artesian Basin, the largest groundwater source in the world.
Map created by National Geographic Maps

PEOPLE & CULTURE

Australia is one of the world's most ethnically diverse nations. Nearly a quarter of the people who live in Australia were born in other countries. They come from the United Kingdom and other European countries, but also from China, Vietnam, North Africa, and the Middle East.

Australia's warm, sunny climate and abundance of open spaces gives the population a love of the outdoors. The people are also passionate about sports, including swimming, surfing, sailing, tennis, soccer, cricket, rugby, and their own invention, Australian rules football.

Australia's ecosystem is an unusual one because of its remote location. As a result, there are many animal species that occur here and nowhere else in the world, such as the platypus, kangaroo, echidna, and koala. Australia has 516 national parks to protect its unique plants and animals.

One of Australia's most amazing sites rises like an enormous whale's back from a flat red-soil desert called the Red Center. This site is called Uluru, and it is a sacred natural formation at the heart of the country. Rising 1,100 feet (335 meters) tall, it is the largest rock in the world!

Australia is home to many of the deadliest species of animals on the planet. There are 36 species of poisonous funnel-web spiders in eastern Australia. There are also 20 types of venomous snakes, including the taipan, which attacks without warning and bites repeatedly, killing its victim in minutes.

There are several types of rain forests in Australia. Tropical rain forests, mainly found in the northeast, are the richest in plant and animal species. Subtropical rain forests are found near the mid-eastern coast, and broadleaf rain forests grow in the southeast and on the island of Tasmania.

GOVERNMENT

As a commonwealth of the United Kingdom, Australia's head of state is the British monarch. Many Australians think the country should end its ties to Britain and become a republic. In a vote in 1999, Australians decided against separating from the UK, but the vote was close, and the debate continues.

Australia is an important exporter of agricultural goods like wool, wheat, beef, fruit, and wine. The country is also rich in minerals and metals and is the world's fourth largest producer of gold.

Aboriginal people arrived in Australia about 50,000 years ago. They may have traveled from Asia across land bridges that were exposed when sea levels were lower. The hardy Aborigines have learned to live in the harsh conditions of the outback.

Dutch explorers first landed in Australia in 1606, and the British began to settle there in 1788. Many settlers were criminals sent to live in Australia as punishment. For a short time, the newcomers lived peacefully with the Aboriginal people. But soon, fighting broke out over who owned the land.

In 1851, gold was discovered in Australia. A rush to find riches brought thousands of new immigrants, and by 1859, six separate colonies existed. In 1901, these colonies joined to form a British commonwealth.

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Australia Country Profile - National Geographic Kids

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Australia is the only country in the world that covers an entire continent. It is one of the largest countries on Earth.

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Recursos educativos (Completar): skeletal system (lengua extranjera - 4º primaria - bones) - complete the gaps

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English

A class by Joe

Past Simple

To talk about: 1. Something that happened once in the past: Example: 'We went to Spain on holiday.' 2. Something that happened several times in the past: Example: 'When I was a child, I walked to school every day.' 3. something that was true for some time in the past: Example: 'I lived in the USA for a year.' 4. we often use expressions with 'ago' with the past simple: Example: 'I met my wife a long time ago.'

When do we use the past simple?

Regular Verbs

For regular verbs, we add -ed. Word examples: play - played, watch - watched, want - wantedSentence examples: 'I played video games last night.''She watched the football match yesterday.'

How do we use the past simple?

What are the original forms of the verbs used in the sentences?

She slept very well last night.

He had toast for breakfast this morning.

I went to the cinema yesterday.

Sentence Examples

Click on the button for a a list you can save and print (there are 2 pages).

Irregular Verbs

Regular verbs are easy but there are lots of irregular verbs in English. Here are the most common irregular verbs with their past tense forms:

How do we use the past simple?

When we use the negative, we don't change the main verb. We use 'didn't' or 'did not' instead. I didn't watch TV yesterday. I did not watch TV yesterday. They didn't go to school last week.They did not go to school last week.

Negative Sentences

Negative

You were late for school this morning.

The concert wasn't amazing.The concert was not amazing.You weren't late for school this morning. You were not late for school this morning.

Be careful!For negatives add 'n't' or 'not'.

Remember! I was You wereShe was He wasIt was We were They were

'Be' is a special verb and we use 'was' or 'were' for the past simple, depending on who you are talking about.

The concert was amazing!

The Verb 'be'

Negative Form

Read the rules and examples and click on the 'questions' tabs to do the activities.

That was easy, right? Now try something a lttle more difficult!

Now click on the buttons below to practice. Read the rules and examples and enjoy the games!

If you want to practice more, click on the buttons for extra activities and games.

Extra activities

Well Done!

Great Job!

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An online class to learn and practice the English past simple.

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Expressing the Future

1. 4 ways to express Future

" We're going to England next year".

¨I promise I will help you. ¨

¨ I'm playing tennis with John today.¨

¨ The train leaves at 4:30.¨

4 ways to express Future

¨ I'm going to spend Christmas in France. ¨.

¨ He's going to eat less sugar this year. ¨

Prediction with evidence

¨ Look at those clouds! It's going to rain.¨

¨ The sun will come up tomorrow. ¨

Certain to happen

Offer, request

Prediction with evidence

¨ I don't think he'll be on time.¨

Present Continuous

¨ Alex and I are having lunch this afternoon. "

Arrangement

¨ Tonight we're playing football. ¨

Plan with other people in near future
Present Simple

¨ Alex and I like eating sandwiches. "

¨ I play football each Thursday."

Exact time
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Lorem ipsum dolor sit amet, consectetur adipiscing elit. Proin urna leo, porta at porta et, venenatis nec dui.

"There is no genius without a touch of madness."

A GREAT CLASS

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Expressing the Future 1. 4 ways to express Future " We're going to England next year". ¨I promise I will help you. ¨ ¨ I'm playing tennis with John today.¨ ¨ The train leaves at 4:30.¨ 4 ways to express Future ¨ I'm going to spend Christmas in France. ¨.

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LIVING THINGS

5th Grade

2. The Cell

INDEX

1. Characteristics of Living Things

3. Organization of Living Things

4. Classification of Living Things

5. Quiz

CHARACTERISTICS OF LIVING THINGS

LIVING THINGS CARRY OUT THE THREE VITAL FUNCTIONS

INTERACTION

NUTRITION

REPRODUCTION

INTERACTION: to respond to stimuli from the environment and from inside our body.

NUTRITION: to extract nutrients from food to obtain energy.

REPRODUCTION: to produce offspring similar to ourselves

ALSO LIVING THINGS...

Can growAre made up of cellsHave an internal organizationAre classified into kingdoms

THE CELL

Living things are made up of cells. A cell is the smallest living structure on Earth. Cells are living things because they carry out the three vital functions (nutrition, interaction and reproduction)

UNICELLULAR ORGANISMS

Some living things are made up of just one cell; we call them unicellular (Eg.: some bacteria and algae). The organelles inside the cell are in charge of carrying out the three vital functions.

MULTICELLULAR ORGANISMS

Some living things are made up of several cells of different types; we callUnicellular Vs. Multicellular them multicellular. (Eg.: animals, plants, most of fungi...). In these living thing, cells are specialized in different functions.

WHAT IS A CELL?

Irregular shapeMembrane (to protect the cell)Cytoplasm (which contains organelles)Several small vacuoles (to store water)Nucleus (to control the cell and store de genetic information).

ANIMAL VERSUS PLANT CELL

Animal cell

Plant cell

Regular shapeMembraneCytoplasm, which contains organellesJust one large vacuoleNucleusHard cell wall, to protect the cellChloroplasts, to carry out photosynthesis

ANIMAL VERSUS PLANT CELL

Animal cell

Plant cell

ORGANIZATION OF LIVING THINGS

An organism is made up of millions of cells, which organize themselves according to the function that they carry out inside an organism.

CLASSIFICATION OF LIVING THINGS

Living things can be classified into five kingdoms

ANIMAL KINGDOMThey are multicellular organisms.They eat other living things.They can move.They have a nervous system and sense organs

PLANT KINGDOMThey are multicellular organisms.They use sunlight to carry out photosynthesis.They make their own food.They can't move.

FUNGI KINGDOMThey can be unicellular or multicellular.They don't make their own food; they have to feed off the remains of dead animals or plants.Mushrooms and yeasts belong to this group.

MONERA KINGDOMThey are unicellular or multicellular.Bacteria belong to this kingdom.We can find them anywhere.

PROTIST KINGDOMMost of them live in the water.They can be unicellular or multicellular.Protozoans and algae belong to this kingdom.Algae can make their own food through photosynthesis.

THE END

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LIVING THINGS 5th Grade 2. The Cell INDEX 1. Characteristics of Living Things 3. Organization of Living Things 4. Classification of Living Things 5. Quiz CHARACTERISTICS OF LIVING THINGS LIVING THINGS CARRY OUT THE THREE VITAL FUNCTIONS INTERACTION NUTRITION REPRODUCTION INTERACTION: to respond to stimuli from the environment and from inside our body.

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In this video from QUEST produced by KQED, get step-by-step instructions on how to make a simple LED battery. Also see a demonstration of how a five-cent LED battery works.

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Natural & Social Science Levels 1-6 Pupil's Online Activities

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Your digital book Natural & Social Science Levels 1-6 Pupil's Online Activities from %publisher includes interactive content and activities that check your answers automatically. Download your content and access it with and without Internet connection from your smartphone, tablet, or computer. Need help? Contact us! help@blinklearning.com

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Este sitio web utiliza cookies de terceros con la finalidad de analizar el uso que hace de nuestra web y personalizar el contenido de los anuncios. Si continúa navegando entendemos que acepta su uso.

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Este sitio web utiliza cookies de terceros con la finalidad de analizar el uso que hace de nuestra web y personalizar el contenido de los anuncios. Si continúa navegando entendemos que acepta su uso.

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How your muscular system works - Emma Bryce

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Welcome to LearnEnglish Teens

Covid-19 learning support: LearnEnglish Teens wants to support students who can't go to school at the moment. You can find tips and advice for learning at home on our new support page.

LearnEnglish Teens is brought to you by the British Council, the world's English teaching experts. If you want to learn English while having fun, this free website is just for you. LearnEnglish Teens can help improve your English with reading, writing and listening practice, tips for exams, grammar and vocabulary exercises, games and videos. You can also interact with other teenagers from all around the world. If you want to learn English in your own country, find a face-to-face course near you.

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British Council LearnEnglish Teens | Free resources for teens to help improve your English

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Covid-19 learning support: LearnEnglish Teens wants to support students who can't go to school at the moment. You can find tips and advice for learning at home on our new support page. LearnEnglish Teens is brought to you by the British Council, the world's English teaching experts.

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The human body is an amazing machine. Learn more about it through movies, quizzes, articles, and more.

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Bones | The Dr. Binocs Show | Learn Videos For Kids

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Home
PET Home

About PET

Writing

Listening

Reading

Speaking

The Cambridge PET exam is the exam following the KET exam, and the exam before the FCE.

To pass the KET you must have the level of English that would let you go on holiday in an English speaking country without someone to translate for you.

The PET means that you have enough English to survive in an English speaking country for a longer period, for example as a student.

Only when you have the FCE can you really say "I speak English".

The PET

This exam is in 4 parts. The parts are - reading, writing, listening and speaking. Sometimes you might do the speaking and listening in the same place on the same day. You ALWAYS do the reading and the writing together.

All four parts of the exam have the same value - 25% each.

Your total mark is made by adding all these results together. You need to get more than 70% to pass the exam. There is no minimum for each paper, so you can pass even if you get 0 for one part (but it will be very difficult).

The mark you get after the test is one of these - f ail: narrow fail: pass: pass with merit. If you fail, your result will also tell you where your English was worst.
©2006 Biscuit Software

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Home PET Home About PET Writing Listening Reading Speaking The Cambridge PET exam is the exam following the KET exam, and the exam before the FCE. To pass the KET you must have the level of English that would let you go on holiday in an English speaking country without someone to translate for you.

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Learn all about bones and muscles, discover fascinating facts and did-you-knows, see videos and images and play games

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lesson a word order in questions 1 learn english

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Oxford University Press, English Language Teaching - elt.enquiry@oup.com

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Drop-down multiple choice | English File Student's Site | Oxford University Press

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Students >English File Student's Site >Pre-intermediate third edition >Vocabulary >Prepositions >Drop-down multiple choice

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VALUES

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Locomotor system for kids - Bones and Muscles of the Human Body

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https://www.symbaloo.com/mix/year612

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YEAR 6 ( no audio)

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WEEK 1-Y6 Key for Schools(Plus)-fusionado

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MEFP (Ceuta, Melilla, centros en el exterior y CIERD - Centro Integrado de Enseñanzas Regladas a Distancia), Aragón, Cantabria, Castilla La Mancha, Castilla y León, Extremadura, Islas Baleares y La Rioja. Material para el alumnado

Competencia en comunicación lingüística. Español.

Competencia en comunicación lingüística. Inglés.

Competencias básicas en ciencia y tecnología
Material para el profesorado (guías de codificación)
Pruebas de la evaluación de 6.º curso de Educación Primaria. Curso 2018-2019 (publicación oficial en preparación)

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MEFP (Ceuta, Melilla, centros en el exterior y CIERD - Centro Integrado de Enseñanzas Regladas a Distancia), Aragón, Cantabria, Castilla La Mancha, Castilla y León, Extremadura, Islas Baleares y La Rioja. Material para el alumnado Competencia en comunicación lingüística. Español. Competencia en comunicación lingüística. Inglés.

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LIGHT, MAGNETISM and ELECTRICITY

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The Musculoskeletal System | Educational Videos for Kids

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- please read © Copyright
All the materials on these pages are free for homework and classroom use only. You may not redistribute, sell or place the content of this page on any other website or blog without written permission from the author Mandy Barrow.

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please read © Copyright All the materials on these pages are free for homework and classroom use only. You may not redistribute, sell or place the content of this page on any other website or blog without written permission from the author Mandy Barrow.

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The Women’s and Children’s Health Network (WCHN) is South Australia’s leading provider of health services for children, young people and women. The WCHN works in partnership with clients and families, the community and other service providers to promote, maintain and restore health.

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How Does the Skeletal System (Bones) Work? (Video)

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Human Skeleton and Types of Joints | Biology Video | Iken Edu

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Recursos educativos (Mapa Interactivo): Bones of the Human Skeleton (biology - 2º Bachillerato - skeletal system) - Select the correct bone according to the showed name.

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The awesome nature of electricity is overwhelming. A single blast of lighting could easily provide enough power to power one hundred light bulbs for over a day. Electricity is a type of energy it usually resides in two forms. Static electricity is formed when electricity gathers in one location. Moving electricity is referred to as current electricity. The innovation of battery technologies has really taken the forefront of the new designs and use of electricity as we move for a greener tomorrow. This section touches on electromagnetism which is usually a larger part of a physics curriculum. As technology continues to explode and we continue to invent new methods for using electricity our need for electricity grows. If we compare the amount of electricity consumed in the United States in 1950 compared to today, the nation consumes sixteen times more electricity today. This demand will only continue to grow as our population increases.

These worksheets will explore all the different ways that use energy to power things or how we store it in the form of batteries. We examine the anatomy of batteries and light bulbs. We explore how simple circuits operate and how switches can help you harness their design. We eventually expand on to calculating the awesome power of these things. We help students learn how to calculate the current, voltage, and resistance a system exerts. We finish off by exploring more complex uses of this energy in the form of electric motors, transformers, and generators. These are the types of worksheets that you would most likely find in Physical Science classes. We focus on the movement of electric current and the use of batteries and cells.

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The awesome nature of electricity is overwhelming. A single blast of lighting could easily provide enough power to power one hundred light bulbs for over a day. Electricity is a type of energy it usually resides in two forms. Static electricity is formed when electricity gathers in one location.

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how to make a model of a hand - Google Search

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What Are Bones and What Do They Do?

Bones provide support for our bodies and help form our shape. Although they're very light, bones are strong enough to support our entire weight.

Bones also protect the organs in our bodies. The skull protects the brain and forms the shape of the face. The spinal cord, a pathway for messages between the brain and the body, is protected by the backbone, or spinal column. The ribs form a cage that shelters the heart and lungs, and the pelvis helps protect the bladder, part of the intestines, and in women, the reproductive organs.

Bones are made up of a framework of a protein called

collagen , with a mineral called calcium phosphate that makes the framework hard and strong. Bones store calcium and release some into the bloodstream when it's needed by other parts of the body. The amounts of certain vitamins and minerals that you eat, especially vitamin D and calcium, directly affect how much calcium is stored in the bones.

Bones are made up of two types of bone tissues:

1. Compact bone is the solid, hard outside part of the bone. It looks like ivory and is extremely strong. Holes and channels run through it, carrying blood vessels and nerves.

2. Cancellous (pronounced: KAN-suh-lus) bone, which looks like a sponge, is inside compact bone. It is made up of a mesh-like network of tiny pieces of bone called trabeculae (pronounced: truh-BEH-kyoo-lee). This is where bone marrow is found.

In this soft bone is where most of the body's blood cells are made. The bone marrow contains stem cells, which produce the body's red blood cells and platelets, and some types of white blood cells. Red blood cells carry oxygen to the body's tissues, and platelets help with blood clotting when someone has a cut or wound. White blood cells help the body fight infection.

Bones are fastened to other bones by long, fibrous straps called ligaments (pronounced: LIG-uh-mentz). Cartilage (pronounced: KAR-tul-ij), a flexible, rubbery substance in our joints, supports bones and protects them where they rub against each other.

How Do Bones Grow?

The bones of kids and young teens are smaller than those of adults and contain "growing zones" called growth plates. These plates consist of multiplying cartilage cells that grow in length, and then change into hard, mineralized bone. These growth plates are easy to spot on an X-ray. Because girls mature at an earlier age than boys, their growth plates change into hard bone at an earlier age.

Bone-building continues throughout life, as a body constantly renews and reshapes the bones' living tissue. Bone contains three types of cells:

1. osteoblasts (pronounced: AHS-tee-uh-blastz), which make new bone and help repair damage

2. osteocytes (pronounced: AHS-tee-o-sites), mature bone cells which help continue new born formation

3. osteoclasts (pronounced: AHS-tee-o-klasts), which break down bone and help to sculpt and shape it

What Are Muscles and What Do They Do?

Muscles pull on the joints, allowing us to move. They also help the body do such things as chewing food and then moving it through the digestive system.

Even when we sit perfectly still, muscles throughout the body are constantly moving. Muscles help the heart beat, the chest rise and fall during breathing, and blood vessels regulate the pressure and flow of blood. When we smile and talk, muscles help us communicate, and when we exercise, they help us stay physically fit and healthy.

Humans have three different kinds of muscle:

1. Skeletal muscle is attached by cord-like tendons to bone, such as in the legs, arms, and face. Skeletal muscles are called striated (pronounced: STRY-ay-ted) because they are made up of fibers that have horizontal stripes when viewed under a microscope. These muscles help hold the skeleton together, give the body shape, and help it with everyday movements (known as voluntary muscles because you can control their movement). They can contract (shorten or tighten) quickly and powerfully, but they tire easily.

2. Smooth, or involuntary, muscle is also made of fibers, but this type of muscle looks smooth, not striated. We can't consciously control our smooth muscles; rather, they're controlled by the nervous system automatically (which is why they're also called involuntary). Examples of smooth muscles are the walls of the stomach and intestines, which help break up food and move it through the digestive system. Smooth muscle is also found in the walls of blood vessels, where it squeezes the stream of blood flowing through the vessels to help maintain blood pressure. Smooth muscles take longer to contract than skeletal muscles do, but they can stay contracted for a long time because they don't tire easily.

3. Cardiac muscle is found in the heart. The walls of the heart's chambers are composed almost entirely of muscle fibers. Cardiac muscle is also an involuntary type of muscle. Its rhythmic, powerful contractions force blood out of the heart as it beats.

How Do Muscles Work?

The movements your muscles make are coordinated and controlled by the brain and nervous system. The involuntary muscles are controlled by structures deep within the brain and the upper part of the spinal cord called the brain stem. The voluntary muscles are regulated by the parts of the brain known as the cerebral motor cortex and the cerebellum (pronounced: ser-uh-BEL-um).

When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa.

The cerebellum coordinates the muscle movements ordered by the motor cortex. Sensors in the muscles and joints send messages back through peripheral nerves to tell the cerebellum and other parts of the brain where and how the arm or leg is moving and what position it's in. This feedback results in smooth, coordinated motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it. When you run, the messages to the brain are more involved, because many muscles have to work in rhythm.

Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can't push them back to the original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Then, when the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint. For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contracts. Then the biceps relaxes and the triceps contracts to straighten the elbow.

What Are Joints and What Do They Do?

Joints are where two bones meet. They make the skeleton flexible - without them, movement would be impossible.

Joints allow our bodies to move in many ways. Some joints open and close like a hinge (such as knees and elbows), whereas others allow for more complicated movement - a shoulder or hip joint, for example, allows for backward, forward, sideways, and rotating movement.

Joints are classified by their range of movement:

Immovable, or fibrous, joints don't move. The dome of the skull, for example, is made of bony plates, which move slightly during birth and then fuse together as the skull finishes growing. Between the edges of these plates are links, or joints, of fibrous tissue. Fibrous joints also hold the teeth in the jawbone.

Partially movable, or cartilaginous (pronounced: kar-tuh-LAH-juh-nus), joints move a little. They are linked by cartilage, as in the spine. Each of the vertebrae in the spine moves in relation to the one above and below it, and together these movements give the spine its flexibility.

Freely movable, or synovial (pronounced: sih-NO-vee-ul), joints move in many directions. The main joints of the body - such as those found at the hip, shoulders, elbows, knees, wrists, and ankles - are freely movable. They are filled with synovial fluid, which acts as a lubricant to help the joints move easily.

Three kinds of freely movable joints play a big part in voluntary movement:

1. Hinge joints allow movement in one direction, as seen in the knees and elbows.

2. Pivot joints allow a rotating or twisting motion, like that of the head moving from side to side.

3. Ball-and-socket joints allow the greatest freedom of movement. The hips and shoulders have this type of joint, in which the round end of a long bone fits into the hollow of another bone.

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Bones provide support for our bodies and help form our shape. Although they're very light, bones are strong enough to support our entire weight. Bones also protect the organs in our bodies. The skull protects the brain and forms the shape of the face.