How do our bodies get information through the sense of touch? Nick was desperate. His paper for History class was due in an hour, but the thermostat in the computer lab wasn’t working and it was freezing in there! Pulling on his ski glove liners, he tried to finish typing the paper. “Hey man, whadda ya doin’?” Dave mumbled as he walked in. “Me?” said Nick. “Trying to type my paper. Hey, what happened to you?? Your face looks lopsided.” “Yeah,” said Dave, “I hadda go to the dentist—now my face is numb. Man, I can’t feel a thing when I touch it. Why are you wearing gloves??” “I’m freezing in here,” said Nick, “but I’ve got to type this paper. Boy, this isn’t working. I can’t feel where one key ends and the next one begins. I’m making too many mistakes!” “Yeah, we’re a matched pair,” said Dave. I can’t feel anything on my face, and you can’t feel anything with your fingers.” What’s going on here? Are Nick’s and Dave’s problems really alike? What has happened to their senses of touch?
We hardly think about our sense of touch until something goes wrong—trying to find a small object with gloves on, waiting for dental anesthetic to wear off so our faces don’t feel “dead.” What a relief when things are back to normal! Just how does the skin let the brain know what it is touching?
You’ve noticed that when you want to find out whether something is smooth or rough, you run your fingertips over it, rather than the palm of your hand or your elbow. And you may have noticed that you can feel a tiny fragment of a bone in your mouth, but you wouldn’t have noticed it at all if you had stepped on it with your bare foot. What does it mean when part of your body is “better” at getting touch information?
Your teacher will discuss in class the parts of the touch sensory system and how they work. This system includes special receptors in the skin, nerve cells or neurons and their extensions called axons that form pathways where the messages travel, and areas of the brain that receive messages and interpret them. After your class discussion and experiment, try to figure out what had happened to Nick and Dave. 1
HOW SENSITIVE IS MY SKIN?
data recording sheets
1. Write the Lab Question and then write your predictions in the boxes above. 2. Follow your teacher’s instructions for choosing a data recorder, a subject, and a tester for your group. Let your teacher know if you do not want to be a subject. 3. Find the Data Recording Sheet at the end of this Student Guide and begin the experiment with the first skin area on the list, the forehead. 4. The subject must either close his/her eyes or wear a blindfold. (The subject may not watch the procedure—this would give away the answer!) 5. The tester should use a cork with two toothpicks stuck into it. You can use one cork and move the toothpicks different distances apart, or use several corks, each one with two toothpicks a measured distance apart. Your teacher will give further 2
instructions on how to do this. The tester should start with toothpicks about 50 millimeters (mm) apart. Make sure that the two points touch the skin at the same time.
6. The data recorder asks how many points the subjects feels. If the person feels two, move the points closer together—about 40 mm apart, and check again. Continue the procedure until you find the smallest distance the points can be separated for the person to feel two points instead of one. When the person reports “one point” for the first time, move the two points apart only one or two millimeters at a time and try to make a very accurate measurement. 7. When the...