This experiment is used to compare skin sensitivity at different parts of the body. Fig. 1 shows a student using a two-point discriminator on the fingertip ...
Question 1 Report
This experiment is used to compare skin sensitivity at different parts of the body. Fig. 1 shows a student using a two-point discriminator on the fingertip and then on the upper arm of a volunteer. The two blunt points are pressed gently onto the skin at the same time. The student records the smallest separation at which the volunteer reports feeling two points rather than one. The fingertip normally has a much smaller separation than the upper arm.
(a) Identify the type of receptor being investigated. [1]
(b) Explain why the points of the discriminator must not break the skin. [1]
(c) Use Fig. 1 to describe how the student should find the threshold separation for one body area. [3]
(d) Explain why the fingertip can detect two points closer together than the upper arm. [3]
(e) Suggest two steps the student should take to reduce risk or improve the quality of the results. [2]
Answer Details
(a) Touch receptor / pressure receptor / mechanoreceptor [1] (b) To avoid injury / pain triggering a pain receptor rather than only touch receptors [1] (c) Start with the points separated [1]; reduce the separation in small measured steps [1]; record the smallest distance reported as two points, repeating trials [1] (d) Fingertip has a greater density of touch receptors [1]; receptors have smaller receptive fields / are closer together [1]; two nearby points stimulate separate receptors, producing separate impulses [1] (e) Any two: clean the equipment between volunteers [1]; use gentle equal pressure [1]; repeat each measurement [1]; volunteer closes eyes / does not see separation [1]; obtain consent [1]
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