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Stem Up

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The Mighty Musculoskeletal System Read & Learn How do your bones and muscles work together?

Craft Build your own Skeleton!

The Science Communication Club

Volume 01 Issue 01

Meet the Team Diana Nelles // Director Diana is an undergraduate student specialising in pharmacology and toxicology at the University of Toronto. She hopes to spark a scientific interest and curiosity within the community by organizing interactive events and projects that promote STEM for all ages.

Hayley McKay // Writer Hayley is a graduate student studying plant molecular genetics at the University of Toronto. Outside of the lab, she writes exciting and informative stories about science in an effort to connect and engage more people in STEAM (Science, Technology, Engineering, Art & Math).

Melissa Wong // Writer Melissa is an undergraduate student studying pharmacology at the University of Toronto. She is excited about writing articles and organizing events that promote science communication within and outside the local community.

Shanling Lei // Illustrator Shanling is an undergraduate student studying life sciences at the University of Toronto. She communicates complex ideas in science through fun and creative illustrations.

Eugenia Yi // Illustrator Shanling is an undergraduate student at the University of Toronto’s Faculty of Arts and Sciences. She creates engaging and interactive illustrations for anyone interested in the sciences.

Amy Zhang // Layout Designer Amy is a digital illustrator pursuing her graduate studies in biomedical communication at the University of Toronto. She wants to create art that gets people excited about interacting with science.


Table of Contents 4 The Skeletal System 8 Muscles in the Human Body 13 Muscles, Movements and Reflexes 16 Spinal Muscle Atrophy 18 Osteoporosis 22 Crossword 24 Word Search 25 Build your own Skeleton



Skeletal System Written by Melissa Illustrated by Eugenia


allowe’en! It’s that time of the year again! Everyone is all dressed up and there is one costume that makes an appearance every year, the skeleton! The skeleton is a light-weight structure made up of bones. The skeleton gives our body shape and allows us to move around – otherwise we would just be a blob!


The Skeleton We’re all born with a skeleton, in fact, a baby is born with 300 bones – which is more bones than an adult (206 bones)! Where did all our bones go as we age? Babies have a lot of cartilage – the flexible material that make up our ears – and as we age our cartilage gets replaced by bone. Through this process, our bones fuse (join) together and this is why adults have less bones than babies! Our bones also protect our organs. For example, the skull protects our brain – that being said, always wear a helmet when biking, skateboarding, or performing activities that might cause head injuries to protect the skull. Our ribs protect our lungs and heart (and other organs in the chest area), and our spine protects our spinal cord so that the signals from our brain can be sent to the various parts of our bodies, such as the signal directing our legs to walk to the next house for candy on Hallowe’en! Our spine is made of ring-shaped bones called vertebrae and we have 33 vertebrae in our spine!


If we zoom in on our bones, we should be able to identify three types of cells. The first type of cell is the bone cell, called the osteocyte. The next type of cell is called the osteoblast and its job is to form bone through a process called ossification. The third type of cell is involved in repair and its job is to break down bone! This cell is called the osteoclast. We don’t want to have too much or too little bone, and this is why we have cells specialized at forming bone (osteoblasts) and cells specialized at breaking down bone (osteoclasts). 6

Bones are often portrayed as being inanimate, but they are far from it as our bones are constantly being formed and repaired! We need calcium to build bones, but calcium’s BFF, vitamin D, is needed for calcium to work the best. The best way to obtain calcium and vitamin D is from drinking milk, or beverages such as soy milk that are fortified with these nutrients. We can also make our bones stronger through exercise! This can be as simple as taking a walk in the park!

The skeletal system can do many things – giving us shape, support, and protection – but it can’t do all this on its own. It needs to work with the muscular system which we will talk about in the next section!

Fun fact: Did you know that the largest bone in our body is in our thigh? This bone is called the femur.

Fun fact: Did you know that the smallest bone in our body sits behind our eardrum? This bone is called the stapes and it’s less than 1 cm in length. 7

Muscles in the Human Body Written by Hayley Illustrated by Eugenia 8


id you know you have more than 650 muscles in your body? These muscles help you move, but they also keep you alive – a lot of the time, you don’t even have to think about them! But what is a muscle, other than some fleshy stuff here and there around your body? Muscles are made up of a material that is sort of like an elastic band. It’s

composed of tiny fibres that can shorten and lengthen when given a signal from your brain, a process called muscle contraction and relaxation. There are a few different kinds of muscles in your body: skeletal, smooth and cardiac. You can read a little more about each kind on the next page: 9

Skeletal Muscles


When you think of a muscle, you usually think about this kind, these muscles give your body strength and support. Skeletal muscles are controlled by you, so they can help you do things like carry your bag of Hallowe’en candy or rake leaves in your backyard. In order to move your limbs,

skeletal muscles are attached to the ends of your bones by things called tendons. Tendons are made of very tough material so they can withstand all the moving your bones and muscles do every day!

Skeletal muscles come in lots of shapes and sizes – did you know the largest muscle in your body is called the gluteus maximus? You might know it as the fleshy pillow you sit on, aka your bum! You can find other large and strong muscles in your legs, like in your thighs. These muscles, also known as quadriceps, are important for

keeping you upright and can get very strong with lots of running, biking, skiing and other athletic activities. But let’s not forget about your calves, the muscles on the lower part of your legs that give you that spring in your step – these are called soleus muscles.

There are of course many muscles in your upper body too! When you lift your big heavy pumpkin out of the pumpkin patch, a bunch of your arm, chest and back muscles are working together to help you carry it. The biceps at the front of your upper arm and triceps at the back of your upper arm help you hold onto the pumpkin, while the

pectoralis major muscles in your chest and the deltoid muscles in your shoulders help you stand up straight and carry it all the way home.

Can you find all these muscles on the skeleton?


Smooth Muscles Smooth muscles are mostly found inside your organs and they are what’s known as involuntary muscles. This means you can’t control them, no matter how hard you try. Smooth muscles are shaped like sheets and have lots of layers all attached together. In your digestive system, each organ has a few layers of smooth muscles which help your organs push all those candy apples you’ve eaten along so you can digest them. You can also find smooth muscles in your eyes. Have you ever looked in the mirror in the dark, then turned on the light? If you have, you probably noticed your pupils (the dark black circles in the middle of your eyes) get smaller. This happens when smooth muscles in your eyes relax when there’s bright light and allow your pupils to close. 12

Cardiac Muscles Cardiac muscles are a special set of muscles found in your heart that help you pump blood around your body. You also can’t control these – they work as an independent team to contract and relax so your heart beats on time. Cardiac muscles are also extremely thick and strong. They have to be able to pump blood from your heart to the tips of your toes in a fraction of a second! Now that you’ve learned about the different kinds of muscles in your body, let’s go to the next section to learn how they work together with the skeletal system and the brain to let you move around.

Muscles, Movement & Reflexes Written by Hayley Illustrated by Shanling & Eugenia


hen you decide you want to take a step, or lift your arm, how does this thought get converted into a movement? Once the thought enters your mind, your brain sends a signal to your muscles to contract which causes your bones to move, since they are connected to your muscles by tendons. Movements like walking or typing on a

computer require a lot of different muscles to act, all at the same time. Your brain has to signal to each and every muscle needed for the movement and tell those muscles what to do and when. This may sound like a pretty difficult task, but your muscles and brain have been practicing since you started moving around as a baby! 13

When you repeat the same movement over and over, you develop what’s called muscle memory. This is when your brain and muscles learn how to do a certain thing after lots of practice, without too much effort. It’s like they say: once you learn, you never forget how to ride a bike! But have you ever experienced your body reacting to something without you thinking about it? Maybe a scary figure has popped out at you in a haunted house and made you jump, or you accidentally touched something hot and your hand recoiled instantly. These are a class of movements called reflexes.


Your body is always aware of what’s going on around you, and reflexes are your body’s way of responding quickly to things that might be dangerous. It’s a built-in safety system where your brain is alerted to a threat and signals to your muscles to respond accordingly without you having to process what happened first. Say someone dressed in a scary werewolf costume is hiding in a big pile of leaves, and as you walk by, they jump out and startle you. If you’ve ever experienced something like this, you might have felt your jaw tighten, eyes close, head jerk back, shoulders and arms rise, and legs tense up. All these movements

happened because your brain saw the person in the costume as a threat and signalled to your muscles to contract and move your body to positions that help you defend yourself. Involuntary reactions like this are meant to protect us, but we also have a few reflexes that are left over from before humans even existed. Maybe you’re watching a scary movie and something really creepy happens – you might notice you got goosebumps on your skin. Goosebumps are also a reflex caused by your brain signalling to tiny muscles under your skin that contract to make all your hairs stand up straight.

Although it’s not really helpful to us now, if our ancestors (who had a lot more hair on their bodies) became frightened, they would develop goosebumps too. But since they were much hairier, having all their hairs stand on end would make them look much bigger and scarier to help defend themselves against whatever they saw as a threat. If you think about it, the musculoskeletal system is a pretty amazing thing. With direction from your brain, your muscles and bones allow you to move however you want, and keep your body safe and functioning without you having to think about it.


U Spinal Muscular Atrophy Written by Melissa Illustrated by Shanling 16

nfortunately, some people are unable to receive directions from their brain for their muscles to move the way they want. An example is a disease called Spinal Muscular Atrophy (also known as SMA) where the muscle cells aren’t receiving signals from the brain to allow the muscles to move. Remember when we talked about how the spine protects our spinal cord so that the signals from the brain can be sent to various parts of our body? Inside our spinal cord is a type of cell called the nerve cell and its job is to pass on important

information from the brain to the different cells in our body, which includes our muscle cells. People with SMA have nerve cells in their spinal cord that are breaking down. When their nerve cells are breaking down, important information from the brain cannot be passed to their muscle cells. Muscles only move when they receive a signal from the brain, but when muscle cells don’t receive the “go” signal to move from the nerve cells – as is the case for people with SMA – their muscles won’t move and will begin to shrink due to their lack of activity. The shrinking

of muscles is called atrophy. When muscle cells are shrinking in these individuals, their muscles weaken and they will have difficulties performing daily activities, such as walking. Luckily, there are tools that are available to help people with SMA in their daily activities! These include leg braces and canes that help people move around and technologies that allow them to easily turn on the lights or T.V. Scientists have also been creating a special type of medicine that they hope will stop the breakdown of nerve cells in the spinal cord. 17

Osteoporosis Written by Melissa Illustrated by Shanling


ave you ever wondered why grownups always tell us to drink milk? If you recall how bones are formed, we need calcium and its BFF, vitamin D, to help us build bones. Calcium and vitamin D are found in milk and are added in beverages like soy milk so that we get enough of these bone building nutrients! But why is getting enough calcium important? There is a bone disease, called osteoporosis, that is the result of having too little bone. Remember, our bones give us support, shape, and protects our organs! When we have too little bone, our bones become prone to fractures. If we look at healthy bones under a microscope, the bones look like a sponge with a lot of holes.


People with osteoporosis have lower bone density, meaning that they have bigger holes due to the loss of bone. This might cause people with osteoporosis to hunch their backs as their vertebrae – the bones that make up the spine – are weakening and shrinking due to the loss of bone.

To prevent having too little bone, our bodies need enough calcium and vitamin D. We can do this by incorporating foods high in calcium, such as milk and yogurt, and foods high in vitamin D, like salmon and egg yolk, in our diet.


In addition to a proper diet, exercise is equally as important! Just like muscles, we need to train our bones so that they will grow to become big and strong! Exercising can also promote muscle and bone formation – think osteoblasts in action!

Research indicates that people have a higher chance of getting bone diseases, like osteoporosis, when we aren’t eating enough foods containing calcium and vitamin D and when we don’t exercise enough. Although we are encouraged to stay at home during the pandemic, this doesn’t mean we have to be sitting on the couch all day! Some simple exercises like walking around your house or doing jumping jacks in your room can help strengthen your muscles and bones!


Activity Booklet What’s Inside?

Crossword Puzzle DIY Skeleton Word Search21

Crossword Puzzle

Musculoskeletal System Edition

Use your lumbrical (hand) muscles to complete the crossword puzzle!


Across 3. Protects the ends of bones and reduces friction between joints 4. A muscle on the front of the thigh 6. Another word for kneecap 8. When a muscle ‘shrinks’ to generate movement 9. Joins two bones together 10. Where two bones meet or connect

Down 1. The largest bone in the human body 2. The largest muscle in the human body 5. Makes up the vertebrate skeleton 7. Joins a muscle and a bone together


The Great Musculoskeletal Word Search

Can you find and circle these words? Biceps Cartilage Fibula Ligaments Quadricep Smooth Muscle Triceps 24

Bones Contraction Gluteus Maximum Patella Relaxation Soleus Cardiac Muscle

Femur Joints Pectoralis Major Skeletal Muscle Tibia

Build your own Skeleton!

Can you attach the numbers and put me back together?


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Answers Crossword F E M G U C A R T I L A U T Q U A D R I C E P U S B M O C O N T R A C X E I L I G A M E U J O I N T S


Copyright Š 2020 by The Science Communication Club All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the publisher, except in the case of brief quotations embodied in critical reviews and certain other noncommercial uses permitted by copyright law. Published on October 31, 2020 The Science Communication Club



The Science Communication Club

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