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Hand Model

Introduction
Public summary: 

Take control of an enormous hand, playing the part of the muscles that control it! Can you work out how to make a fist? Why are there tendons running down both sides of the fingers? And exactly how are your thumbs different to your fingers?

Large working model of a hand and forearm, with all the tendons to show how a hand works.
Useful information
Kit List: 

Working hand model ("Emily").
Short lengths of string (optional)
Small Paper Hand (stored in wallet attached to box)

Packing Away: 

The hand packs together with the lung model for storage. It can be slightly tricky to get this to work, so get someone to show you if you haven't done it before. After fitting them together, strap tightly with the red straps. The two together aren't particularly heavy, but they are bulky and tricky to move so ask for help if needed.
There's a small a4 wallet attached to the wooden frame for storing paper hands.

Frequency of use: 
5
Explanation
Explanation: 

This experiment is a bit of a crowd-pleaser. There is a subtle technique of keeping kids' fingers out of the wooden joints, and after this has been achieved, all ages will be amused by playing with it.

Explanation

1. Guess what the model is of – nice and easy start!
2. Ask what do the pieces of wood represent = bones, and where in the body they are.
3. Talk about moving your fingers, and ask what in the body moves them = muscles (after several shouts of veins, ARGH!!), then where are the muscles that move your fingers = forearm not in the hand, and the fact the muscle belly mostly ends quite before the wrist. You can get them to wiggle their fingers and see if you can see the muscles moving in the forearm, but not above the elbow (this is often more visible on demonstrator/parent than child!)
4. Leads onto the fact that muscles are in forearm, but need to join onto fingers in order to move them – how? Gives off strings that run along fingers and attaches to the bones (show on model) – what are the strings called? = tendons (after more shouts of veins!!). So, to move, muscles contract (tighten up/become shorter), and pull the tendons, which pull the bones.
5. Then let them play around a bit – I usually get them to pick a blue string (but avoid thumb for now), and then a white string, and see the difference between them. Blue string goes all the way to the end bone, so can bend the end joint, whereas white string can’t because it doesn’t attach to the end bone.
6. Get them to bend all the fingers (tests if they’ve remembered which strings bend the fingers)
7. Then ask how to make the fingers straight again. Most will try to push the blue/white strings – tell them that doesn’t work because muscles can only pull. Get them to look at fingers closely and spot any other strings. Eventually they’ll realise to pull the yellow/purple string
8. Ask them why yellow/purple strings makes the fingers straight. If they struggle, get them to see the difference between blue/white and yellow+purple = different sides of the hand. Therefore muscles on front of arm (flexors) pull blue/white tendons on that side, which flex the joints, and vice versa with other side with the extensors.
9. So, all around the body, muscles work in pairs to do opposite actions. Point out biceps on you and say it bends the elbow, then ask where the muscle will be to make it straight = on the other side, triceps.
10. Then ask what’s telling the muscles to contract and pull the tendons = brain. And how = send messages = nerves, and briefly explain concept of nerves sending messages
11. I usually end by saying that to play the piano for example, or type on a keyboard, your fingers have got to move in lots of different ways, so your brain has got to send all those messages in the right order to the right muscles, to pull on the right tendons. So, it’s actually really complicated just to move your fingers.

Thumbs

The pink string pulls the thumb across the palm. You can use this to talk about how thumbs can move in an additional special way so you can pinch things - show them how you can oppose the pads of your thumb and fingers, but not of your fingers. They may have heard of opposable thumbs - some will tell you the word, others will recognise it. You can talk about different animals not having opposable thumbs and thus not being able to use tools etc.

If you've got the short (c. 6 inches) lengths of cord, you can challenge them to tie a simple knot in one. When they triumphantly present you with the resultant knot, get them to do it again without using their thumbs (police this vigilantly, people cheat without even noticing!). Usually this is much much harder. If somehow they do it easily, tell them to undo it without their thumbs. This is more challenging!

General stuff

– Useful to refer to your own or their hand while describing stuff, for example show the extensor tendons on the back of your hand (they’re a lot easier to see in adults than on themselves). Get them to feel the muscles working on themselves or on you. Do this by getting them to place their whole hand over their arm (both sides!) and then wiggling their fingers! Then they have to believe you!
- This can be a good experiment to do with really quite small kids, but keep it nice and simple with them (i.e. I wouldn’t bother talking about tendons, just say ‘stringy like things that pull on our bones to make them move’!)
- This is a great "How-Science-Works" experiment even if you don't know the biology. Ask about how we can find out about how our hands work, we have hands so look how they work. We can feel muscles moving and see tendons. We can get an X-Ray to see the bones, an ultrasound gives us more information on muscles. We can do a dissection too. Then we build a model to test our theory. The paper model is a nice simple model, what can't we do with it? We don't have as much movement, bones aren't as accurate, make the wooden model with more motion.

Additional stuff:

1. Carpal tunnel syndrome:
- Carpal ligament bridges wrist bones, making a small tunnel for nerves and tendons to go through.
- Median nerve goes through – sensation to most of hand (not little finger), and muscle control of some thumb muscles.
- Compression of tunnel walls (due to repeated wrist movements) or swelling (due to injury/arthritis), causes pressure on median nerve
- Symptoms – aches, pins+needles, pain, numbness, loss of fine finger movements e.g. writing.
- Treatment - stretching exercises, anti-inflammatory drugs, surgery (cut carpal ligament = relieve pressure)

2. Difference between ligaments and tendons
- Explain that a joint is where 2 bones come together and they can move. But the bones need something to hold them in place, this is what ligaments do, connect bones to other bones. Tendons connect muscles to bones so they can move the joints.

Risk Assessment
Date risk assesment last checked: 
Sat, 27/01/2018
Risk assesment checked by: 
jaredjeya
Date risk assesment double checked: 
Sat, 27/01/2018
Risk assesment double-checked by: 
Matt Worssam
Risk Assessment: 
DESCRIPTION Wooden Hand model
RISKS Finger trap

Wooden corners - injury risk

Heavy model which moves easily when strings are pulled
ACTION TO BE TAKEN TO MINIMISE RISKS

Do not allow the kids to touch the hand itself when someone is pulling the tendons

Hand is sanded and shaped to try to reduce this.

Do not let the people pulling the tendons get too violent. Hold on to the model to prevent it from sliding along the desk, or place it on the floor if possible.

Ensure kids are behaving sensibly

ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT

Call first aider in event of injury

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Images
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