Students investigate the sensitivity of different areas of the skin using a mathematical compass to stimulate mechanoreceptors.   The procedure asks students to place the points of the compass on different areas, such as the forearm and the palm and have a test subject report whether one point is being felt or two points. 

The compass can then be opened until the subject feels two points.   

Areas of the skin that are more sensitive will distinguish the two points at a much smaller distance.    Activity includes a data table and discussion questions that follow a CER (claim – evidence – reasoning) format and asks students to design an experiment that would test sensitivity to temperature.

The activity is designed to complement lessons on the sensory system where prioprioceptors, mechanoreceptors and thermoreceptors are discussed, though it could be used at any time, prior knowledge is not required.