This lesson covers the topic of muscles. Students learn about the three different types of muscles in the human body and the effects of microgravity on muscles. Students also learn how astronauts need to exercise in order to lessen muscle atrophy in space. Students discover what types of equipment engineers design to help the astronauts exercise while in space.

Engineers need to understand how the human body works in order to help astronauts stay healthy in outer space. The microgravity of outer space leads to muscle atrophy, and so scientists and engineers at NASA work to design special exercise machines to help the astronauts maintain muscle strength during space flight. muscle movement human body exercise astronaut cardiac skeletal atrophy engineer space microgravity voluntary muscle control involuntary muscle control smooth After this lesson, students should be able to: List the three different kinds of muscles. Describe the difference between voluntary and involuntary muscle control. Explain what happens to muscles in outer space. Describe the importance of exercising both on Earth and in outer space. Astronauts get to do all sorts of amazing things! How would you like to visit the International Space station, go on a space walk, or look down on planet Earth from outer space? That would be pretty cool! Yes, astronauts have an incredible job, but it is also a tough one. One of the numerous challenges that astronauts face is to identify and accommodate for the many affects that outer space has on their health. One of these effects is called muscle atrophy ─ which means that when astronauts are away from Earth in a microgravity environment for a long time, their muscles become smaller and much weaker. Essentially, this means that muscles shrink! This is because in outer space, there is very little gravity (microgravity), so there is hardly any force or "load" pulling down on the astronauts' muscles. Here on Earth, we have to constantly resist the force of gravity every day ─ helping to keep our muscles working and strong. But in outer space, the astronauts do not have to resist gravity, so their muscles get weaker and eventually atrophy. According to researchers, after just 5 to 11 days in space, astronauts can lose up to 20 percent of their muscle fibers - that is a lot of loss! What do you know about muscles? Do you know that every person has three different types of muscle in their body? The first type of muscle is called cardiac muscle. These are the muscles in your heart. The second type of muscle is called smooth muscle. These muscles line your stomach and other internal organs. The third type of muscle is skeletal muscle. The muscles are attached to your bones and help you move around. Skeletal muscles are the ones you can see when you flex your arm or leg. Skeletal muscles are also the only muscles that you can move by thinking about them. We call skeletal muscles voluntary muscles because you can volunteer to move them whenever you want to engage (activate) them. Cardiac and smooth muscles are involuntary because they move without you thinking about them. (Write the three muscle types on the board.) We know that if you reduce the loads, or weight, on your muscles, they will atrophy and get weaker. But, the great thing about muscles is that once you put weight on them again, they will begin to grow stronger. That is what happens when a person lifts heavy weights (e.g., weight lifters). Their skeletal muscles react to the repetitive lifting and eventually get stronger. So, the very best thing that astronauts can do to keep their muscles strong is to exercise. The type of exercise the astronauts do is very important - it has to be resistance exercise, which means it has to create a load on their muscles. But, exercising is tricky in outer space! Remember, there is very little gravity, so if an astronaut tried lifting heavy weights, they would feel incredibly light and take little effort to lift. Therefore, how do astronauts get the exercise they need? Engineers at NASA have developed special machines to help astronauts create a load on their muscles, even in microgravity. Even though you may not be an astronaut, you can learn from their example. When people on Earth get older, their physical activity often slows down and their muscles begin to atrophy also, just like in outer space. So, if you want to have strong, healthy muscles when you get old, you need to put loads on your muscles and exercise - just like the astronauts. Today we are going to learn more about muscles and how engineers help keep astronaut's muscles healthy and strong in space. How would you dance, write or smile without your muscles? You couldn't; it would be impossible! Muscles are in charge of all the body's movements. About 40% of the weight of the body is muscle. Some muscles get their instructions from the nervous system, which sends electrical impulses to the muscles telling them to move. However, your heart, which is made up of cardiac muscle, can contract all by itself, without directions from the brain. Muscles get their energy from glucose that is carried in blood cells through the body. The body also stores glucose in the muscles as glycogen. Then, when you exercise, the glycogen is broken down to provide energy. Muscles are made up of fibers. The more a fiber contracts, the shorter the entire muscle becomes. The fibers consist of bundles of myofibril which contains two types of filaments ─ called myofilaments: thin filaments, primarily made of the actin protein, and thick filaments, primarily made of the myosin protein. These myofilaments are bundled together to create myofibrils. These myofibrils are then bundled together to create a skeletal muscle fiber. When a muscle is stimulated, an action potential travels over the muscle fiber membrane and causes a contraction. In a contracted state, the actin (thin) filaments are pulled inward among the myosin (thick) filaments so that the filaments then overlap each other. There are three different types of muscle: skeletal muscle, smooth muscle and cardiac muscle. Of these, only the skeletal muscles are controlled by conscious thought. The muscles visible on the outside of the human body are skeletal muscles. (See Vocabulary for specific types.) Arranged in parallel bundles and attached to bones by tendons, some of the skeletal muscles are the largest and most powerful muscles in the human body. Skeletal muscles include ones located in the arms, legs, neck, tongue and face. Tendons are located wherever there are skeletal muscles, helping to make a powerful movement team by attaching the muscles to bone. The smooth muscles make up hollow internal organs, which include organs such as blood vessels, the gastrointestinal tract and the bladder. They use much less energy than the skeletal muscles and do not require conscious thought to make them work ─ try telling your stomach to contract! Also, the speed of smooth muscle contraction is much slower than the skeletal muscle. The cardiac muscle is the muscle that makes up the walls of the heart. Unlike the skeletal muscle, the heart takes a lifetime to tire. It pumps blood through the entire body continuously. Blood carries oxygen, and the cardiac muscle needs continuous unobstructed oxygen to keep it alive, so when a heart attack occurs (and blood stops flowing) the cardiac muscle rapidly dies. Proteins that make up myofilaments. Skeletal muscles found in the upper arm. Involuntary muscles located in the heart. Skeletal muscles found in the shoulder area. Skeletal muscles found in your behind (rear end). Environment in which there is very little net gravitational force (free-falling). A bundle of myofilaments. The study of muscle. Skeletal muscles found on each side of the upper chest (pecs). Skeletal muscles found at front of your thigh (quads). Skeletal muscles found under the rib cage (abs). Voluntary muscles attached to bone. Involuntary muscles located in the hollow internal organs. Tough tissue that attaches skeletal muscles to the bone. Walk, Run, Jump! Muscles, Muscles Everywhere Let's review the different kinds of muscles. Who can remember what a smooth muscle is and give us some examples? (Answer: Smooth muscles make up hollow internal organs, like the bladder or stomach.) What about skeletal muscles? (Answer: Skeletal muscles are muscles attached to bone that you can see when you exercise.) Who can remember the third type of muscle? (Answer: Cardiac muscles; the muscles in the heart.) Which of the three muscle types is voluntary (i.e., you can move by thinking about them)? (Answer: skeletal) Skeletal muscles are the only voluntary type of muscle. Other muscles are involuntary since we can not control the contraction of our stomach and heart, for example. What do astronauts need to do in space to help keep their muscles strong? (Answer: exercise) What do we need to do here on Earth to keep our own muscles strong? (Answer: exercise) Engineers help keep people's muscles healthy and strong in space by designing special exercise equipment that provides muscle load in a microgravity (little gravity) environment. Discussion Question: Solicit, integrate and summarize student responses. Write their ideas on the board. Tell the students these questions will be answered in the lesson. What do muscles do? (Answer: Help us move, eat, go to the bathroom, play sports, dance, walk, talk, smile, etc.) What do you think happens to our muscles when we travel into outer space? (Answer: They atrophy, or grow weaker/shrink. Note: Write down student ideas on the board.) Do you think engineers need to know about muscles? Why? (Answer: Yes, so that they can help astronauts while traveling in space, and help design ways to take care of people's muscles here on Earth, with devices such as prosthetics, wheelchairs, crutches, special exercise equipment for people with disabilities, etc.) Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Count the votes and write the totals on the board. Give the right answer. True or False: There are four different kinds of muscles. (Answer: False; there are three different kinds of muscle in the human body.) True or False: Some engineers need to know how muscles work (Answer: True) True or False: Astronauts do not need to exercise in outer space (Answer: False; astronauts need to exercise to keep their muscles from atrophying, or shrinking.) True or False: When we get old, our muscles get weaker (Answer: True) True or False: Exercising helps our muscles stay strong (Answer: True) True or False: Rough muscle is one type of muscle (Answer: False, the three types of muscle are cardiac, smooth and skeletal.) True or False: We can control all of our muscles and tell them when to move (Answer: False, we can only control skeletal muscles.) True or False: Cardiac muscle is found in the heart (Answer: True) True or False: Skeletal muscle is voluntary muscle (Answer: True) Human Matching: On ten separate pieces of paper, write the terms and the definitions of the five concepts listed below (each on a separate piece of paper). Ask for ten volunteers from the audience to come up to the front of the room, and give each volunteer one of the pieces of paper. Have all volunteers read what is written on their papers one at a time. Have the audience match term to definition by voting. Have students with "terms" stand by their "definitions." At the end, give a brief explanation of concepts. Smooth muscle — Muscles located in the hollow internal organs (like our stomach or bladder); involuntary Cardiac muscle —Muscles located in the heart; involuntary Skeletal muscle —Muscles attached to bone; voluntary Muscle atrophy — Weakening of our muscles (from microgravity and/or aging) Exercise — Way to keep our muscles strong Talk about the importance of exercising our muscles here on Earth. Have students create a flyer about exercise and exercise equipment for the next space mission. Check out this video of cardiac muscle contracting: http://exploration.nasa.gov/articles/14feb_heart_lite.html Watch the NASA Fitness in Space movie: http://www.nasa.gov/audience/formedia/presskits/ffs_interactive.html Bedford, Anthony and Fowler, Wallace. Engineering Mechanics: Statics/Dynamics, Second Edition, Addison-Wesley Longman, Inc.: New York, 1999. Fox, Stuart. Human Physiology, Ninth Edition, McGraw-Hill Science: New York, 2005. Miller, Karen and Phillips, Tony. National Aeronautics and Space Administration, Systems Mission Directorate at NASA's Marshall Space Flight Center Science@NASA, Patches for a Broken Heart, November 7, 2005, http://exploration.nasa.gov/articles/14feb_heart_lite.html National Aeronautics and Space Administration (NASA), Space Research, The Office of Biological and Physical Research, Pumping Iron in Microgravity, January 22, 2004, http://spaceresearch.nasa.gov/general_info/pumpingiron.html National Aeronautics and Space Administration (NASA), Johnson Space Center, Muscle Atrophy, http://www.nasa.gov/pdf/64249main_ffs_factsheets_hbp_atrophy.pdf National Aeronautics and Space Administration (NASA), Johnson Space Center, Astronaut Fitness/Physical Conditioning, http://www.nasa.gov/pdf/64247main_ffs_factsheets_fitness.pdf Nemours Foundation, Kids Health For Kids, Seeing Skeletal Muscles, 1995-2003, http://kidshealth.org/kid/body/muscles_noSW_p5.html Nemours Foundation, Kids Health For Kids, Your Multitalented Muscles, 1995-2003, http://kidshealth.org/kid/body/muscles_noSW.html Parker, Steve. How the Body Works, ed. Dorling Kindersley Limited, London. Reader's Digest Books: New York, 1999. Petty, John Ira. National Aeronautics and Space Administration (NASA), For Media and Press, Press Kits, Fit for Space Multimedia, "Fitness in Space" (video), February 26, 2006, http://www.nasa.gov/audience/formedia/presskits/ffs_interactive.html U.S. Department of Health and Human Services, The President's Council on Physical Fitness and Sports, Publications, Council Publications, Winning Nutrition for Athletes, October 15, 2004, http://www.fitness.gov/nutrition.html U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, Training Website, Anatomy and Physiology, Muscular System, Muscle Types, http://training.seer.cancer.gov/module_anatomy/unit4_3_muscle_types.html Wikipedia Foundation, Inc. Myofibril, March 21, 2006, http://en.wikipedia.org/wiki/Myofibril