Observing Skin Sensitivity

The senses receive information about the environment and relay it to the central nervous system, where the information is interpreted. The sense organs contain specialized neurons called receptors, each of which is adapted to receive a particular kind of stimulus. The receptors for the sense of touch are scattered all over the surface of the entire body. However, the receptors are more closely grouped together in some areas of the body than in others. In this activity, you will investigate the distribution and sensitivity of the touch receptors of the human body.

Procedure: 1. Obtain a bag of toothpick stimuli sets. Each contains a single toothpick, and four sets of toothpicks taped together and separated by 5mm, 10mm, 15mm, and 20mm. 2. Blindfold your partner. Gently touch your partner’s fingertip with any of the sets of toothpicks. Have your partner identify whether you are using 1 or 2 toothpicks. Record this in your data table. 3. Repeat step 2 with all the sets of toothpicks. 4. Repeat steps 2 and 3 on the palm, back of hand, inside of forearm, and back of the neck. Record all information in the data table. 5. Switch roles and repeat steps 2 -4.

Data Table: Number of stimuli detected Body Part One Toothpicks Toothpicks Toothpicks Toothpicks Toothpick 5mm apart 10mm apart 15mm apart 20mm apart Fingertip Palm of hand Back of hand Inside of forearm Back of neck

Analysis: 1. Of the parts of the body you tested, which part was best able to distinguish between the closest stimuli? Which part was least able to distinguish between the closest stimuli? 2. What does this indicate about the distribution of touch receptors in the skin? 3. How does the arrangement of nerve receptors for touch make the Braille system possible?