How do you feel? No, I don't mean are you happy or sad? Touch the back
of your hand. Did you feel it? How? When you touched your
hand, you pressed on nerves in your skin. These nerves reacted and sent a
message to your
brain, telling you that something touched your hand. Some parts of your
skin have more nerves than others. This week, we are going to examine how
these nerves are arranged. You will need:
two paperclips
your skin
a friend
a ruler
Straighten the first bend of both paperclips. This will let you use each
paperclip as a handle, with a point sticking out for testing. Hold one
paperclip in each hand. Have your friend place an arm on a table or flat
surface and close her eyes. Gently touch the two points to the skin on her
arm, with the points about an inch apart. You don't want it to hurt.
Touch
the skin just enough to feel. Ask her if it feels like one point or two.
If it feels like two points, move them a little closer. If it feels like
one, move them a little farther apart. Try to find the distance where it
shifts from feeling like two points to feeling like one. Measure the distance
with the ruler.
Next, try the same thing on the back of her hand. Again, find out how far
apart the points need to be to have it just feel like one point and measure it.
Try one more time, this time on a fingertip. Be especially gentle here, as
your fingers are more sensitive. How close can you get the points this
time before it feels like one?
What did you find? On the arm, the points could be quite far apart and
still feel like one. Your arm does not need to be very sensitive, as you
don't usually use it to feel things. In your hand, your nerves are closer
together, and so you can feel the individual points much closer. You use
your hand for touching things, so it needs to be more sensitive. In your
fingertip the nerves are so close together that unless the points are touching,
you can still feel both of them. That is what allows people to read
Braille, which is writing made up of patterns of bumps. You would find it
very difficult to read Braille with your arm, or even with the back of your
hand.
This experiment was re-printed with permission from Robert Krampf
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