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Tactile Sensitivity

In this activity, students use a pair of chopsticks to learn that the sense of touch is not restricted to their hands and that different parts of their body have different sensitivities.

The four senses of sight, hearing, smell, and taste are located in specific parts of the body.

The sense of touch is located throughout the body, in your largest organ, the skin. The sense of touch originatees in the bottom layer of your skin called the dermis.

The dermis is filled with many tiny nerve endings that give you information about the things your body is touching. Nerve endings do this by carrying the information to the spinal cord, which sends messages to the brain where the feeling is registered.

The nerve endings in your skin can tell you if something is hot or cold. They can also feel if something is hurting you. Your body has about twenty different types of nerve endings that all send messages to your brain. However, the most common receptors are heat, cold, pain, and pressure or touch receptors. Pain receptors are probably the most important for your safety because they can protect you by warning your brain that your body is hurt.

Some areas of the body are more sensitive than others because they have more nerve endings. It hurts when you bite your tongue because the sides of your tongue have a lot of nerve endings that are very sensitive to pain. Your tongue, however, is not as good at sensing hot or cold. That is why it is easy to burn your mouth when you eat something really hot. Your fingertips are also very sensitive. People who are blind use their fingertips to read Braille by feeling the patterns of raised dots on their paper. 

Objectives

  • Investigate the body’s sense of touch.

Materials

  • Per Student:
    2 Chopsticks or unsharpened pencils

Key Questions

  • Why are the fingertips more sensitive than the back?
  • What are the 4 common skin receptors and why are they important?
  • What is the largest organ of the human body?

What To Do

Teacher tip: Demonstrate how students should be testing for tactile sensitivity before students try the activity.

  1. Divide the students into pairs and give each pair 2 chopsticks.
  2. Explain that they are going to conduct a scientific test on tactile sensitivity or how good their skin is at feeling something.
  3. Ask students to touch their partners gently with the two chopsticks, holding them different distances (e.g., 1cm and 5cm) apart.
  4. One partner should close their eyes and hold out their arm.
  5. The other partner gently touches them with the 2 chopsticks and asks “Is that one chopstick or two?”
  6. Tell the “tester” to try different areas of their partner’s body and different distances between the chopsticks. Testers can try touching the fingers, hands, wrist, forearm, shoulder, back of the neck, cheek, ear or ankle (but only in areas that the partner is comfortable with.)
  7. Then, have the students to switch places with their partner.
  8. Explain that if a body part is not sensitive, the skin cannot tell if it is being touched by one chopstick or two, even if they are quite far apart.

This activity is an accepted scientific test for skin sensitivity and is called a two point discrimination test. The distance between the two chopsticks is called the threshold distance and the closer they are when the student can still detect two chopsticks, the more sensitive the body part.

The receptors in our skin are not distributed in a uniform way around our bodies. Some places, such as our fingers and lips, have more touch receptors than other parts of our body, such as our backs. That is one reason why we are more sensitive to touch on our fingers and face than on our backs. The table below shows the varying sensitivity of our body parts.

Site  Threshold Distance (mm)
Fingers 2-3
Upper lip 5
Cheek 6
Nose 7
Palm 10
Forehead 15
Foot 20
Belly 30
Forearm 35
Upper arm 39
Back 39
Shoulder 41
Thigh 42
Calf 45

This data is from a two-point discrimination threshold experiment (published in The Skin Senses, edited by D. R. Kenshalo, Springfield, IL, 1968.)