Skeletons & Muscles

Activities to try

1. 1

   Elbow rig: discover that muscles pull, never push

   Why it works: A muscle moves a bone only by getting shorter and pulling; it cannot push. Because of this, a second muscle (its antagonistic partner) is needed to actively pull the bone back the other way — one muscle alone cannot both bend and straighten a joint (gravity can let an arm drop, but no muscle can push it).

   1. Look at an arm shown as two hinged 'bones' meeting at the elbow, with a biceps band above and a triceps band below.
   2. Activate (drag/tap) the biceps so it shortens and thickens, and watch the forearm swing UP — note that the muscle got shorter and the bone moved.
   3. Take the challenge: 'Now put the arm back down using ONLY the biceps.' Try, and notice that in the rig (which has no gravity pulling on it) contracting the biceps only pulls the forearm up, so it can never push the arm back down.
   4. Activate the triceps and watch the forearm swing back down; state in your own words why a second muscle was needed.
   5. Feel your own biceps harden as you bend your real elbow (try lifting a light book), then feel it go soft when you let your arm rest straight on a table — connect the rig to what your arm is already doing.
2. 2

   Feel-your-own-body skeleton map and protective bones

   Why it works: The skeleton does three jobs — support, protection and movement — and includes the skull, ribs and spine, not just arms and legs. Named bones protect specific organs (the ribcage curving around the heart and lungs), and living bone is active tissue, not the dry plastic of a display.

   1. Before looking at any diagram, feel your own skull, ribs, backbone and the hinge at your elbow and knee.
   2. On a labelled whole-body skeleton with major bones (skull, ribcage, spine, femur) colour-coded by function, locate each bone you just felt on your own body.
   3. Match protective bones to what they guard: cranium/skull → brain; ribcage → heart and lungs; spine → spinal cord.
   4. Look at how the ribcage wraps around and encloses the heart and lungs — ideally viewing it from more than one side — and tag each bone example to at least one of the three jobs: support, protection, movement.
   5. Open 'myth-buster' flaps and decide: are bones dead and dry, or living tissue? Does an insect have bones inside its hard shell?
3. 3

   Compare body plans: endoskeleton, exoskeleton, no hard skeleton

   Why it works: A bony internal skeleton is one solution among several for support and protection — some animals have a hard external skeleton and some, like worms and jellyfish, have no bones or hard skeleton at all — so 'having a bony skeleton' is not universal and 'hard bits outside' are not bones inside.

   1. Look side by side at a human (bony skeleton inside), a beetle (hard case outside), and an earthworm or jellyfish (no bones).
   2. Describe where the hard supporting structure is for each: inside the body, outside the body, or with no hard parts at all (soft bodies held in shape by fluid or water).
   3. Answer: why can't a jellyfish stand up the way you can — what does your body have that it doesn't?
   4. Explain why an insect's hard shell is NOT the same as having bones inside.