Thermoreceptors: Responding to Heat and Cold

ACTIVITY 2 Thermo-receptors: Responding to Heat and Cold

You can usually tell if a mosquito lands on you even if you cannot see it. The reason for this is that whenever something touches you many receptors in the skin are stimulated. The hair on your skin acts like a mini-antenna. Whenever something touches it, the hair moves and nerves located at the base of the hair respond to the movement.

"Thermo reception" is the response to temperature. Your skin has special nerves called "free nerve endings" which detect temperature. Some are sensitive to heat and others are sensitive to cold. You can tell whether something is hot, warm, cool or cold by how often the heat or cold receptors fire and send information to your brain. You may have jumped into a cold pool or stepped into a hot shower which may have felt uncomfortable at first. This sensation usually disappears as the receptors adapt to the temperature because the free nerve endings become desensitized to the temperature.

In the following activity you will map the location of thermo-receptors in a grid, delineated in 0.5 cm2 increments, stamped on the inside of your forearm

Step 1

Using the rubber stamp and an ink pad, lightly stamp a -grid on a hairless part of your forearm.

Step 2

Safety: Use caution when working with hot liquids.

Place a metal probe in a cup of hot tap water and allow it to remain there for several minutes. Be sure that the tap water temperature does not exceed 60oC. Dry it quickly on a piece of paper towel. You will close your eyes. Your lab partner will quickly touch it to one of the areas in the grid. You will tell your lab partner whether you felt a feeling of warmth. If so, record a (+) in that area of the grid shown below. If you did not feel warmth, record a (-) in the grid. Repeat for the other areas of the grid

COLD RECEPTORS HEAT RECEPTORS

~ What you need ~

Per team (of 2)

1 cup hot water (60oC), 1 cup cold water, 1 ruler, 1 ink pad, 1 metal probe, paper towels, 1 ruber stamp

Step 3

Repeat Step 2 for cold sensation by placing the metal probe in a cup of ice water.

Step 4

Count the number of heat sensitive areas in a square centimeter. Add the number of (+) areas in the grid. Calculate the entire grid area in cm2 by multiplying the length times the width and then determine the number of heat-sensitive points per square centimeter. Repeat calculations for cold sensation.

Exchange places with your lab partner and repeat Steps 1-4.

1. Compare the number of heat and cold receptors per square centimeter with other teams in your class. Were the results the same? Explain.

2. From your calculations, are you more sensitive to heat or to cold? Explain your answer:

Science and Tech 3 / Nervous system / The senses

ACTIVITY 1

Distribution and Sensitivity of Touch Receptors

Your touch receptors are not evenly distributed over your skin. They are more concentrated in some areas of the body. Receptors follow the all-or-none principle. A stimulus must be strong enough for a receptor nerve to notice it and respond to it. This is called the "threshold". The threshold is the minimum level of a stimulus needed to cause a neuron to fire and send a message to your brain.

Touch receptors in some areas are more sensitive than those in other areas of your skin. In this activity, you will investigate the sensitivity and distribution of touch receptors in the skin.

Step 1

Tape 2 toothpicks together so that they are 3mm apart as shown in Figure 2. Measure the distance with a ruler. Make sure the tips of the toothpicks are even with each other. Write "3mm" on the tape. Prepare 4 additional

sets at distances of 6, 9,12,15, and 18mm.

Skin area

Distance apart in mm

Fingertip

Back of the hand

Palm of hand

Arm

Back of neck

~ What you need ~

· Blindfold , Ruler, tape, 12 toothpicks

Step 2

Blindfold your lab partner or have him or her close their eyes. Use the sets of toothpicks in random order and touch your lab partner's skin on the areas shown in the table below. Note the distance at which your lab partner can tell that you are using two toothpicks. Record the numbers in Data Table 2.

Step 3

Switch roles with your lab partner and repeat Step 2.

1. Which skin areas tested showed the most sensitivity to touch?

2. What do your results tell you about the concentration of touch receptors in these areas?

3. What do the results indicate about the distribution of touch receptors in the skin?