The body’s sense of touch is a combination of pressure, pain and temperature. Different parts of the body have different numbers of nerve endings, because it’s more important to be able to detect objects and their temperature using touch on fingertips, lips or tongue rather than the back of the leg.
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Mapping the Sense of Touch
Draw an outline of a person. Using a pair of blunt dividers or a pair of toothpicks, gently touch a partner on arms, legs, hands, feet and back, moving the points of the divider or the toothpicks closer together until they only feel one touch. On the outline, write down the smallest distance where two separate points are felt. The smaller the distance, the more nerve endings there are on that part of the body.
Telling the Difference Using Touch
Fingertips are very sensitive to different textures. Get someone to put a number of objects in a cloth bag or a box with a hand-sized opening, without saying what they are. Ideas include an orange, a spoon, a piece of cloth, a feather, a pinecone, a wooden or plastic letter or number, a bar of soap, a nut in its shell, an acorn, a dice, a rough and a fine piece of sandpaper, a pebble, a pencil, a scrunched up piece of paper, a model animal, and a thimble.
Describe what the objects feel like, and try to work out what they are. Try doing it with gloves on, or with toes – does it make any difference? Try looking at an object outside the bag or box and matching it with one inside.
Reading with Sense of Touch
People with visual impairments read using their sense of touch. This uses a system called Braille, invented by a young visually impaired French man called Louis Braille in the 1820s. Braille uses combinations of six raised dots to represent letters, numbers, punctuation and common combinations of letters or short words, such as ‘OW’, ‘ER’, ‘AND’ or ‘FOR’.
Try making Braille letters using dots of paper stuck onto card, or laying a piece of paper onto a soft surface and using a pencil or pen point to press dots into the back (don’t forget that it needs to be a mirror image). Try reading the Braille letters. How small can you make the letters and tell the difference between the dots. Are fingers better at telling the differences between the dots than the heel of a hand, an elbow, or toes? The parts of the body where it is easier to tell the difference are the parts with more nerve endings.
The nerve ending in the skin can detect temperature as well as pressure. Fill three glasses with water, one as hot as you can comfortably touch, one ice cold, and one at room temperature. Hold the hot glass and the ice-cold glass for one minute, with as much of your palm touching it as possible. Then hold the room temperature glass with both hands – does it feel hot or cold? The glass will probably feel warm to the cold hand and cold to the warm hand. This is because the nerves and the brain are not reporting the exact temperature of the water, but comparing it to the previous temperature.