Investigating Touch and Temperature Receptors (AQA A Level Biology)

• Within the human skin, there are many temperature and touch receptors that enable humans to interpret and respond to their environment
• Experiments can be designed to investigate the sensitivity of temperature receptors and the resolution or habituation of touch receptors

The sensitivity of temperature receptors in human skin

• The temperature of the surrounding environment can be detected by the skin, with warm and cold environments producing different sensations
• Experiments using water baths can investigate the sensitivity of temperature receptors in the human skin

Apparatus

• Thermometer kept in a water bath at 45 °C
• Thermometer kept in a bowl of iced water
• A willing human subject

Method

• Take a thermometer from the water bath kept at 45 °C and wipe it dry with a paper towel. Touch it on the back of the subject’s hand in different places
• Record whether the subject feels any warmth in addition to the touch, or whether only touch can be felt. When only touch is sensed, record the temperature reading on the thermometer
• Repeat using the thermometer kept in iced water. Dry the thermometer and touch it on the back of the subject’s hand in different places. Record whether the subject feels cold in addition to the touch, or whether only the touch can be felt. When only touch is sensed, record the temperature reading on the thermometer.

Results and analysis

• The temperatures recorded from both thermometers will show the limit of the temperature receptor's sensitivity. The receptors can not detect the temperatures within that range
  • These temperatures are likely to be close to the subject's body temperature, this makes it difficult for the receptors to detect the difference

Limitations

• This experiment relies on humans relaying information about sensations they are experiencing. The subject may lie or convince themselves that they can feel warmth or cold when they don't
• Only one human is used
  • Ideally, this experiment would be repeated using a number of different humans in order to achieve more reliable results

Resolution of touch receptors in human skin

• Different areas of the skin have different numbers of touch receptors present
• The number or concentration of touch receptors present can affect the resolution in that area
  • This is the ability of the human to distinguish between two different points of contact on the skin

• Areas with a 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

• A blunt pair of scissors
• A die
• A ruler
• A willing blindfolded human subject

Method

• Open the scissors as wide as possible
  • Make sure to be very careful with the scissors so that you do not cut anyone

• Roll the die and if the result is odd, touch the subject's forearm with only one point of the scissors. If the result is even, then touch with both points of the scissors
• Ask the subject whether they felt one or two points of contact
• Record how many points they were touched with and the answer they gave. Repeat this step roughly 10 times.
• If the subject's answers were mostly correct, reduce the distance between the points of the scissors. If their answers were mostly incorrect, increase the distance between the points of the scissors
• Repeat steps 2 - 5
• When you think you have found the minimum distance at which the subject is able to reliably discriminate between two points measure and record the distance between the two points of the scissors
• Repeat the procedure using a different part of the body

• Areas such as the fingers and soles of the feet tend to have a much higher resolution
  • This means the distance between the two scissor blades will be very small

• Areas such as the back of the hands and legs tend to have lower resolution
  • This means the distance between the two scissor blades will be larger

Limitations

• This experiment relies on humans relaying information so there is a chance of human error
• Only one human is used
  • Ideally, this experiment would be repeated using a number of different humans in order to achieve more reliable results

A measurement can be made between the points of the two scissor blades

Habituation of touch receptors in human skin

• Over time touch receptors in the skin can become habituated to certain stimulus
  • Habituation is when a response to a stimulus decreases after repeated or prolonged exposure to that stimulus

• For example, individuals can become unaware of the clothing they are wearing after a period of time
• Experiments investigating the habituation of touch receptors in human skin can be difficult to design and carry out, especially in a school environment
• A form of touch (or multiple different types of touch) would be applied to a humans body part for a sustained period of time. They would be asked how the sensation changes over time
  • 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 used. Recent studies have revealed that habituation to touch differs on both the group and individual level