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The Muscular System moves the body, gives it posture and circulates the blood. It is made up of three types of muscles: skeletal, smooth & cardiac muscles.


KidsHealth: Your Muscles
DK Find Out! Muscular System
KidsHealth Interactive Diagram: Muscles & Joints
Wonderopolis: Why Do Athletes Stretch Before They Work Out?
Wonderopolis: What Is the Strongest Muscle in the Body?
Wonderopolis: Why Do Your Muscles Cramp?
BBC Human Anatomy: Muscle Diagram

Science in Context: Muscular System is a database you can use in any IndyPL Library Branch or at home with your IndyPL Library Card. Login using your library card number and PIN. What’s My PIN? It will show you biographies, magazines, videos and more about the Excretory System.​

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The skeleton acts like a shield for our vital organs, such as our brain and heart. The skull protects the brain, the ribcage protects the lungs and heart, and the backbone wraps all the way around the spinal cord.

Ligaments connect bones to other bones.

Bone density measures how healthy a bone is – it shows how much mineral matter there is in a square centimetre of bone.

Bone marrow is a tissue found inside bones. Bone marrow is part of the lymphatic system, which plays an important role in the immune system – how our body fights diseases.

Bones have three parts:

  1. The periosteum is a thin membrane on the outer surface – it contains the bone’s nerves and blood vessels.
  2. Underneath this is cortical bone – also called compact bone – which is smooth and hard.
  3. Cancellous bone is located in layers within compact bone – it’s sometimes called spongy bone because it has little holes in it.

There are six different kinds of fractures: complete, greenstick, single, comminuted, bowing and open. Doctors use x-rays to help them decide how to set the broken bones so they can join back up with new cells and blood vessels.

Bones need calcium to keep healthy. Calcium can be found in dairy products, dark green leafy vegetables, nuts, orange juice and soy.

Vitamin D helps the body and bones absorb calcium – fish and egg yolks both have vitamin D in them.

There are four main kinds of bones:

  1. Long
  2. Short
  3. Irregular
  4. Flat


There are three kinds of muscles – smooth, cardiac and skeletal.

Smooth muscles and cardiac muscles are also called involuntary muscles, because they move without you telling them to.

Skeletal muscles are also called voluntary muscles, because you can control when you move them.

When muscles feel sore, it can be because of a strain – the muscle fibres have torn a bit and need time to heal. This happens if you’ve picked up something very heavy, or if you’ve been doing a lot of running and jumping.

Another type of muscle injury is a sprain – this happens when a tendon is pulled.

There are four main muscle shapes:

  1. Spindle-shaped muscles, which are thick in the middle and thinner at the ends, such as your biceps and triceps in your arm
  2. Flat muscles, such in your forehead
  3. Triangular muscles, such as the deltoid muscles in your shoulder
  4. Circular muscles, which are shaped like rings, such as around your mouth

Words to know:

biceps – the muscles in your upper arms
calcium – the mineral that bones need to keep healthy
cancellous bone – a type of bone is located within layers of compact bone, and is sometimes called spongy bone because it has tiny holes in it
compact bone – the smooth, hard part of the bone underneath the periostium, which is what you’ll see when you look at a skeleton
deltoid – the muscles in your shoulders
fracture – the term for a broken bone; there are six different kinds of fractures: complete, greenstick, single, comminuted, bowing and open
involuntary muscles – muscles that you do not control, such as in your heart and stomach
ligaments – strong cords of tissue that connect bones to other bones
osteoporosis – a disease that causes bones to lose density, making them more likely to break
pelvis – the bones at our hips
periostium – the thin membrane covering the outside of the bone, containing nerves and blood vessels
ribcage – a series of connected horizontal bones in your chest that protect the heart and lungs
skeletal muscles – muscles attached to your skeleton with tendons
skull – the bones in our head that protect the brain
sprain – an injury called by pulling a tendon
strain – a muscle injury that can make them feel sore if you’ve picked up something very heavy, or done more running than you’re used to.
tendons – strong cords of tissue that connect muscles to bones
vertebrae – the bones surrounding our spinal cord
vitamin D – helps the body absorb calcium
voluntary muscles – muscles that you can control moving, such as the ones in your arms and legs


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