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Unit 19: Biology Part 2 Page 109 of 137

Experiment: Can You Feel It?

Every bit of your skin has sensory neurons. These neurons sense pain,
pressure, and temperature, and send the message to your brain. This is the
sense of touch. Not all parts of your body have the same amount of
neurons, and the more neurons a certain body part has, the more sensitive
it will be to touch. In this experiment, you’ll use indirect evidence to figure
out if you have more neurons in your palm or lower back.

Materials:

 2 washcloths
 Water
 Partner

1. Prepare two washcloths – one with cool water and one with slightly
warm water. The two washcloths should not be dramatically different
in temperature, but there should be some difference.
2. Have a partner place a washcloth on your palm 20 times. He or she
should not tell you which washcloth it is, and should not do it in any
kind of pattern. Your job is to tell if it is the cool or warm washcloth
that is being touched to your palm.
3. Have your partner record how many times you answered correctly.
4. Repeat steps two and three placing the washcloth on your lower back.

What’s Happening: Your palm has more sensory neurons than your lower
back, so you should have had an easier time identifying cool versus warm on
this part of your body. This means your palm is also more sensitive to

pressure and pain. Now that you have compared the palm and lower back,
why not compare some other parts of your body?

Experiment: The Nose Knows (Or Does It?)

Our sense of smell is controlled by sensory neurons in the nose. When a
smell is detected, a message is sent to the brain. What the brain does with

the information in some cases may surprise you.

Materials:

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