Investigating Touch and Temperature Receptors (AQA A Level Biology): Revision Note

Investigating touch and temperature receptors in skin

• It is possible to investigate receptors in human skin, e.g.:

  • sensitivity of temperature receptors

  • habituation of touch receptors

  • resolution of touch receptors

Investigating the sensitivity of temperature receptors in human skin

Apparatus

• A thermometer

• A water bath at 45 °C

• A bowl of iced water

• A willing human subject

Method

1. Take a thermometer from a water bath kept at 45 °C and wipe it dry with a paper towel

2. Touch the thermometer on the back of the subject’s hand in different places

3. For each touch, record:

   • the temperature on the thermometer

   • whether the subject feels warmth, or whether only touch can be felt

4. Repeat steps 1-3 using the thermometer kept in iced water

Results and analysis

• The results should show that the temperature receptors on the skin can only detect temperature when it deviates significantly from body temperature; when the thermometer reaches a temperature that is close to body temperature then only touch will be felt

Limitations

• This experiment relies on humans relaying information about sensations they are experiencing; the subject may convince themselves that they can feel warmth or cold when they don't

• The results are subjective

• Only one subject is used

  • Ideally, this experiment would be repeated using a number of different subjects in order to achieve more reliable results

Investigating habituation of touch receptors in human skin

• Over time touch receptors in the skin can become habituated to certain stimuli; this means that response to a stimulus decreases after repeated or prolonged exposure

  • E.g. individuals usually become unaware of the clothing they are wearing after a period of time

Method

1. Select a human subject and ensure they are seated comfortably with their eyes covered

   • Covering the eyes prevents sight of the stimulus from influencing perceived touch

2. Use a soft, standardised stimulus, such as a cotton bud, soft brush, or piece of thread

3. Start a stopwatch and then gently apply the stimulus to the same spot, e.g. the back of the hand or forearm; the stimulus could be applied:

   • at regular intervals, e.g. once every 2 seconds

   • as steady, light pressure

4. Ask the subject to observe any point at which they can no longer feel the stimulus; this is evidence of habituation

5. Record the time at which the subject no longer perceives the stimulus

6. After a rest period of 1–2 minutes, repeat the procedure to observe whether the sensitivity returns

7. Repeat with multiple volunteers and test different areas of skin, e.g. back of neck, palm, forearm, to compare results

Limitations

• Maintaining the same intensity of touch for a long period of time can be difficult; a machine is usually required

• There is likely to be a large variation in the results if multiple subjects are use; recent studies have revealed that habituation to touch differs widely between individuals

Investigating resolution of touch receptors in human skin

• The number of touch receptors present affects the resolution of the skin, i.e. the ability to distinguish between two different points of contact

  • Areas with high resolution have a large number of touch receptors so they are able to identify two points of contact even if they are extremely close together

Apparatus

• Blunt pair of scissors, or an unfolded paperclip

• Die

• Ruler

• A human subject

Method

1. Open scissors or paperclip to a measured distance, e.g. 4 cm

   • Use a ruler to confirm the exact spacing

2. Ensure that the subject is seated comfortably with their eyes covered

3. Randomly apply either one point or two points simultaneously to the same area of the skin, e.g. forearm

   • Pressure should be gentle and even

   • Randomness can be achieved by throwing a die and applying one point for an odd number and two points for an even number

4. Ask the subject to report whether they felt one or two points

5. Record the number of points applied and whether or not the subject’s response was correct in a results table

6. Repeat steps 3-5 at least twice more at the same distance

7. Reduce the distance between the points and repeat steps 3-6

8. Continue adjusting the distance until you determine the minimum distance at which the subject can correctly identify two points

9. Repeat the procedure on a different area of the body, e.g. fingertip, back of hand, or neck

Results and analysis

• Areas such as the fingers and soles of the feet tend to have a much higher resolution

  • Two points of contact can be identified by a subject when the points are very close together

• Areas such as the back of the hands and legs tend to have lower resolution

Limitations

• This experiment relies on humans relaying information, so there is a chance of human error

• Only one subject is used

  • Ideally, this experiment would be repeated using a number of different subjects in order to achieve more reliable results